Hospital-Acquired Infections

Definition
Description
Causes
Diagnosis
Treatment
Prevention

Definition

A hospital-acquired infection, also called a noso-comial infection, is an infection that first appears between 48 hours and four days after a patient is admitted to a hospital or other healthcare facility.

Description

About 10% of patients admitted to acute care hospitals and long-term care facilities in the United States develop a hospital-acquired, or nosocomial, infection, with an annual total of 1.7 million infections and 99,000 deaths as of 2007. The annual cost of treating these infections is estimated to run between $4.5 billion and $11 billion. Hospital-acquired infections are usually related to a device, procedure, or treatment used to diagnose or treat the patient’s initial illness or injury. The Centers for Disease Control (CDC) of the U.S. Department of Health and Human Services has shown that many of these infections are preventable through the adherence to strict guidelines by healthcare workers when caring for patients. What can make these infections so troublesome is that they occur in people whose health is already compromised by the condition for which they were first hospitalized.

Hospital-acquired infections may be caused by bacteria, viruses, fungi, or parasites. These microorganisms may already be present in the patient’s body or may come from the environment, contaminated hospital equipment, healthcare workers, or other patients. There are three basic routes of infection transmission: direct contact (diseases are spread by touching infected objects or persons); droplet (diseases are spread by coughing and sneezing); and airborne (diseases are spread by microorganisms that remain suspended in the air for long periods of time).

Depending on the causal agents involved, an infection may start in any part of the body. A localized infection is limited to a specific part of the body and has local symptoms. For example, if a surgical wound in the abdomen becomes infected, the area around the wound becomes red, hot, and painful. A generalized infection is one that enters the bloodstream and causes systemic symptoms such as fever, chills, low blood pressure, or mental confusion. This can lead to sepsis, a serious, rapidly progressive multi-organ infection, sometimes called blood poisoning, that can result in death.

Hospital-acquired infections may develop from the performance of surgical procedures; from the insertion of catheters (tubes) into the urinary tract, nose, mouth, or blood vessels; or from material from the nose or mouth that is aspirated (inhaled) into the lungs. According to the CDC, the most common types of hospital-acquired infections are urinary tract infections (UTIs) (32%), surgical wound infections (22%), pneumonia (15%), and bloodstream infections (14%). The University of Michigan Health System reports that the most common sources of infection in their hospital are urinary catheters, central venous (in the vein) catheters, and endotracheal tubes (tubes going through the mouth into the stomach). Catheters going into the body allow bacteria to move along the outside of the tube into the body where they find their way into the bloodstream. A study in the journal Infection Control and Hospital Epidemiology shows that about 24% of patients with catheters will develop catheter-related infections, of which 5.2% will become bloodstream infections. Death has been shown to occur in 4-20% of catheter-related infections.

Hospital-acquired infections in the United States are monitored by the National Healthcare Safety Net-work (NHSN), formed in 2005 by a merger of three health surveillance systems previously established by the CDC. The NHSN monitors healthcare personnel safety as well as patient safety.

Causes

All hospitalized patients are at risk of acquiring an infection from their treatment or surgery. Some patients are at greater risk than others, especially young children, the elderly, and persons with compromised immune systems. The surveillance database compiled by the CDC shows that the overall infection rate among children in intensive care is 6.1%, with the primary causes being venous catheters and ventilator-associated pneumonia. The risk factors for hospital-acquired infections in children include parenteral nutrition (tube or intravenous feeding), the use of antibiotics for more than 10 days, use of invasive devices, poor postoperative status, and immune system dysfunction. Other risk factors that increase the opportunity for hospitalized adults and children to acquire infections are:

KEY TERMS

Abscess— A localized pocket of pus at a site of infection.

Aseptic— Sterile conditions with no harmful microorganisms present.

Catheter— A thin, hollow tube inserted into the body at specific points in order to infuse medications, blood components, or nutritional fluids into the body, or to withdraw fluids from the body such as gastric fluid or urine.

Culture— A swab of blood, sputum, pus, urine, or other body fluid planted in a special medium, incubated, and allowed to grow for identification of infection-causing organisms.

Generalized infection— An infection that has entered the bloodstream and has general systemic symptoms such as fever, chills, and low blood pressure.

Localized infection— An infection that is limited to a specific part of the body and has local symptoms.

Nosocomial infection— An infection acquired in the hospital.

Sepsis— A rapidly spreading state of poisoning in the body, usually involving the whole body.

• a prolonged hospital stay
• severity of underlying illness
• compromised nutritional or immune status
• use of indwelling catheters
• failure of health care workers to wash their hands between patients or before procedures
• prevalence of antibiotic-resistant bacteria from the overuse of antibiotics

Any type of invasive (enters the body) procedure can expose a patient to the possibility of infection. Some common procedures that increase the risk of hospital-acquired infections include:

• urinary bladder catheterization
• respiratory procedures such as intubation or mechanical ventilation
• surgery and the dressing or drainage of surgical wounds
• gastric drainage tubes into the stomach through the nose or mouth
• intravenous (IV) procedures for delivery of medication, transfusion, or nutrition

Urinary tract infection (UTI) is the most common type of hospital-acquired infection and has been shown to occur after urinary catheterization. Catheterization is the placement of a catheter through the urethra into the urinary bladder to empty urine from the bladder; or to deliver medication, relieve pressure, or measure urine in the bladder; or for other medical reasons. Normally, a healthy urinary bladder is sterile, with no harmful bacteria or other microorganisms present. Although bacteria may be in or around the urethra, they normally cannot enter the bladder. A catheter, however, can pick up bacteria from the urethra and give them an easy route into the bladder, causing infection. Bacteria from the intestinal tract are the most common type to cause UTIs. Patients with poorly functioning immune systems or who are taking antibiotics are also at increased risk for UTI caused by a fungus called Candida. The prolonged use of antibiotics, which may reduce the effectiveness of the patient’s own immune system, has been shown to create favorable conditions for the growth of this fungal organism.

Invasive surgical procedures, the second most common cause of nosocomial infections, increase a patient’s risk of getting an infection by giving bacteria a route into normally sterile areas of the body. An infection can be acquired from contaminated surgical equipment or from the hands of healthcare workers. Following surgery, the surgical wound can become infected from contaminated dressings or the hands of healthcare workers who change the dressing. Other wounds can also become easily infected, such as those caused by trauma, burns, or pressure sores that result from prolonged bed rest or wheel chair use.

Pneumonia is the third most common type of hospital-acquired infection. Bacteria and other microorganisms are easily introduced into the throat by treatment procedures performed to treat respiratory illnesses. Patients with chronic obstructive lung disease, for example, are especially susceptible to infection because of frequent and prolonged antibiotic therapy and long-term mechanical ventilation used in their treatment. The infecting microorganisms can come from contaminated equipment or the hands of healthcare workers as procedures are conducted such as respiratory intubation, suctioning of material from the throat and mouth, and mechanical ventilation. Once introduced through the nose and mouth, microorganisms quickly colonize the throat area. This means that they grow and form a colony, but have not yet caused an infection. Once the throat is colonized, it is easy for a patient to aspirate the microorganisms into the lungs, where infection develops that leads to pneumonia.

Bloodstream infections are the fourth most common type of hospital-acquired infections. Many hospitalized patients need continuous medications, transfusions, or nutrients delivered into their bloodstream. An intravenous (IV) catheter is placed in a vein and the medications, blood components, or liquid nutritional components are infused into the vein. Bacteria from the surroundings, contaminated equipment, or healthcare workers’ hands can enter the body at the site of catheter insertion. A local infection may develop in the skin around the catheter. The bacteria can also enter the blood through the vein and cause a generalized infection. The longer a catheter is in place, the greater the risk of infection.

Other hospital procedures that may put patients at risk for nosocomial infection are gastrointestinal procedures, obstetric procedures, and kidney dialysis.

Symptoms

Fever is often the first sign of infection. Other symptoms and signs of infection are rapid breathing, mental confusion, low blood pressure, reduced urine output, and a high white blood cell count . Patients with a UTI may have pain when urinating and blood in the urine. Symptoms of pneumonia may include difficulty breathing and inability to cough. A localized infection begins with swelling, redness, and tenderness on the skin or around a surgical wound or other open wound, which can progress rapidly to the destruction of deeper layers of muscle tissue, and eventually sepsis.

Diagnosis

An infection is suspected any time a hospitalized patient develops a fever that cannot be explained by the underlying illness. Some patients, especially the elderly, may not develop a fever. In these patients, the first signs of infection may be rapid breathing or mental confusion.

Diagnosis of a hospital-acquired infection is determined by any of the following:

• evaluation of symptoms and signs of infection
• examination of wounds and catheter entry sites for redness, swelling, or the presence of pus or an abscess
• a complete physical examination and review of underlying illness
• laboratory tests, including complete blood count (CBC), especially to look for an increase in infection fighting white cells; urinalysis, looking for white cells or evidence of blood in the urinary tract; cultures of the infected area, blood, sputum, urine, or other body fluids or tissue to find the causative organism
• chest x ray may be done when pneumonia is suspected to look for the presence of white blood cells and other inflammatory substances in lung tissue
• review of all procedures performed that might have led to infection

Treatment

Cultures of blood, urine, sputum, other body fluids, or tissue are especially important in order to identify the bacteria, fungi, virus, or other microorganism causing the infection. Once the organism has been identified, it will be tested again for sensitivity to a range of antibiotics so that the patient can be treated quickly and effectively with an appropriate medicine to which the causative organism will respond. While waiting for these test results, treatment may begin with common broad-spectrum antibiotics such as penicillin, cephalosporins, tetracyclines, or erythromycin.

More and more often, however, some types of bacteria are becoming resistant to these standard antibiotic treatments, especially when patients with chronic illnesses are frequently given antibiotic therapy for long periods of time. When resistance develops, a different, more powerful, and more specific antibiotic must be used to which the specific organism has been shown to respond. Two strong antibiotics that have been effective against resistant bacteria are vancomycin and imipenem, although some bacteria are developing resistance to these antibiotics as well. A newer generation of tetracycline antibiotics known as glycylcyclines was introduced in 2005; the first of these, tigecycline, was developed specifically to target drug-resistant microorganisms. The prolonged use of antibiotics is also known to reduce the effectiveness of the patient’s own immune system, sometimes becoming a factor in the development of infection.

Fungal infections are treated with antifungal medications. Examples of these are amphotericin B, nys-tatin, ketoconazole, itraconazole, and fluconazole.

Viruses do not respond to antibiotics. A number of antiviral drugs have been developed that slow the growth or reproduction of viruses, such as acyclovir, ganciclovir, foscarnet, and amantadine.

Prevention

Hospitals take a variety of steps to prevent noso-comial infections, including:

• Adoption of an infection control program such as the one sponsored by the Centers for Disease Control (CDC), which includes quality control of procedures known to lead to infection, and a monitoring program to track infection rates to see if they go up or down.
• Employment of an infection control practitioner for every 200 beds.
• Identification of high-risk procedures and other possible sources of infection.
• Strict adherence to hand-washing rules by healthcare workers and visitors to avoid passing infectious microorganisms to or between hospitalized patients.
• Strict attention to aseptic (sterile) technique in the performance of procedures, including use of sterile gowns, gloves, masks, and barriers.
• Sterilization of all reusable equipment such as ventilators, humidifiers, and any devices that come in contact with the respiratory tract.
• Frequent changing of dressings for wounds and use of antibacterial ointments under dressings.
• Removal of nasogastric (nose to stomach) and endotracheal (mouth to stomach) tubes as soon as possible.
• Use of an antibacterial-coated venous catheter that destroys bacteria before they can get into the bloodstream.
• Preventing contact between respiratory secretion sand health care providers by using barriers and masks as needed.
• Use of silver alloy-coated urinary catheters that destroy bacteria before they can migrate up into the bladder.
• Limitations on the use and duration of high-risk procedures such as urinary catheterization.
• Isolation of patients with known infections.
• Sterilization of medical instruments and equipment to prevent contamination.
• Reductions in the general use of antibiotics to encourage better immune response in patients and reduce the cultivation of resistant bacteria.

Resources

BOOKS

Ayliffe, Graham, and Mary English. Hospital Infection: From Miasmas to MRSA. New York: Cambridge University Press, 2003.

Mayhall, C. Glen, ed. Hospital Epidemiology and Infection Control, 3rd ed. Philadelphia: Lippincott Williams and Wilkins, 2004.

PERIODICALS

Crane, S. J., D. Z. Uzlan, and L. M. Baddour. “Bloodstream Infections in a Geriatric Cohort: A Population-Based Study.” American Journal of Medicine 120 (December 2007): 1078–1083.

Edwards, Jonathan R., et al. “National Healthcare Safety Network (NHSN) Report, Data Summary for 2006, Issued June 2007.” American Journal of Infection Control 35 (June 2007): 290–301.

Kilgore, M. L., K. Ghosh, C. M. Beavers, et al. “The Costs of Nosocomial Infections.” Medical Care 46 (January 2008): 101–104.

Rose, W. E., and M. J. Rybak. “Tigecycline: First of a New Class of Antimicrobial Agents.” Pharmacotherapy 26 (August 2006): 1099–1110.

Wang, L., and J. F. Barrett. “Control and Prevention of MRSA Infections.” Methods in Molecular Biology 391 (2007): 209–225.

ORGANIZATIONS

Centers for Disease Control and Prevention (CDC). 1600 Clifton Road, Atlanta, GA 30333. 404-639-3311. http://www.cdc.gov/health/ (accessed April 1, 2008).

National Healthcare Safety Network (NHSN). Division of Healthcare Quality Promotion, MS-A24, Centers for Disease Control and Prevention, 1600 Clifton Road, NE, Atlanta, GA 30333. (800) 893-0485. http://www.cdc.gov/ncidod/dhqp/nhsn_members.html (accessed April 1, 2008).

OTHER

Centers for Disease Control and Prevention (CDC). Questions and Answers about Healthcare-Associated Infections. Atlanta, GA: CDC, 2007.

Siegel, J. D., et al. Guideline for Isolation Precautions: Preventing Transmission of Infectious Agents in Healthcare Settings, June 2007. Atlanta, GA: CDC, 2007.

Toni Rizzo

L. Lee Culvert

Rebecca Frey, PhD

Hospital-Acquired Infections

Definition

A hospital-acquired infection is usually one that first appears three days after a patient is admitted to a hospital or other health care facility. Infections acquired in a hospital are also called nosocomial infections.

Description

About 5-10% of patients admitted to hospitals in the United States develop a nosocomial infection. The Centers for Disease Control and Prevention (CDC) estimate that more than two million patients develop hospital-acquired infections in the United States each year. About 90,000 of these patients die as a result of their infections. Hospital-acquired infections usually are related to a procedure or treatment used to diagnose or treat the patient's illness or injury. About 25% of these infections can be prevented by healthcare workers taking proper precautions when caring for patients.

Hospital-acquired infections can be caused by bacteria, viruses, fungi, or parasites. These microorganisms may already be present in the patient's body or may come from the environment, contaminated hospital equipment, health care workers, or other patients. Depending on the causal agents involved, an infection may start in any part of the body. A localized infection is limited to a specific part of the body and has local symptoms. For example, if a surgical wound in the abdomen becomes infected, the area of the wound becomes red, hot, and painful. A generalized infection is one that enters the bloodstream and causes general systemic symptoms such as fever, chills, low blood pressure, or mental confusion.

Hospital-acquired infections may develop from surgical procedures, catheters placed in the urinary tract or blood vessels, or from material from the nose or mouth that is inhaled into the lungs. The most common types of hospital-acquired infections are urinary tract infections (UTIs), pneumonia, and surgical wound infections.

Causes and symptoms

All hospitalized patients are susceptible to contracting a nosocomial infection. Some patients are at greater risk than others—young children, the elderly, and persons with compromised immune systems are more likely to get an infection. Other risk factors for getting a hospital-acquired infection are a long hospital stay, the use of indwelling catheters, failure of healthcare workers to wash their hands, and overuse of antibiotics.

Any type of invasive procedure can expose a patient to the possibility of infection. Common causes of hospital-acquired infections include:

• urinary bladder catheterization
• respiratory procedures
• surgery and wounds
• intravenous (IV) procedures

Urinary tract infection (UTI) is the most common type of hospital-acquired infection. Most hospital-acquired UTIs happen after urinary catheterization. Catheterization is the placement of a catheter through the urethra into the urinary bladder. This procedure is done to empty urine from the bladder, relieve pressure in the bladder, measure urine in the bladder, put medicine into the bladder, or for other medical reasons.

The healthy urinary bladder is sterile, which means it doesn't have any bacteria or other microorganisms in it. There may be bacteria in or around the urethra but they normally cannot enter the bladder. A catheter can pick up bacteria from the urethra and allow them into the bladder, causing an infection to start.

Bacteria from the intestinal tract are the most common type to cause UTIs. Patients with poorly functioning immune systems or who are taking antibiotics are also at risk for infection by a fungus called Candida.

Pneumonia is the second most common type of hospital-acquired infection. Bacteria and other microorganisms are easily brought into the throat by respiratory procedures commonly done in the hospital. The microorganisms come from contaminated equipment or the hands of health care workers. Some of these procedures are respiratory intubation, suctioning of material from the throat and mouth, and mechanical ventilation. The introduced microorganisms quickly colonize the throat area. This means that they grow and form a colony, but do not yet cause an infection. Once the throat is colonized, it is easy for a patient to inhale the microorganisms into the lungs.

Patients who cannot cough or gag very well are most likely to inhale colonized microorganisms into their lungs. Some respiratory procedures can keep patients from gagging or coughing. Patients who are sedated or who lose consciousness may also be unable to cough or gag. The inhaled microorganisms grow in the lungs and cause an infection that can lead to pneumonia.

Surgical procedures increase a patient's risk of getting an infection in the hospital. Surgery directly invades the patient's body, giving bacteria a way into normally sterile parts of the body. An infection can be acquired from contaminated surgical equipment or from healthcare workers. Following surgery, the surgical wound can become infected. Other wounds from trauma, burns, and ulcers may also become infected.

Many hospitalized patients need a steady supply of medications or nutrients delivered to their bloodstream. An intravenous (IV) catheter is placed in a vein and the medication or other substance is infused into the vein. Bacteria transmitted from the surroundings, contaminated equipment, or healthcare workers' hands can invade the site where the catheter is inserted. A local infection may develop in the skin around the catheter. The bacteria also can enter the blood through the vein and cause a generalized infection. The longer a catheter is in place, the greater the risk of infection.

Other hospital procedures that put patients at risk for nosocomial infection are gastrointestinal procedures, obstetric procedures, and kidney dialysis.

Fever is often the first sign of infection. Other symptoms and signs of infection are rapid breathing, mental confusion, low blood pressure, reduced urine output, and a high white blood cell count.

Patients with a UTI may have pain when urinating and blood in the urine. Symptoms of pneumonia may include difficulty breathing and coughing. A localized infection causes swelling, redness, and tenderness at the site of infection.

Diagnosis

An infection is suspected any time a hospitalized patient develops a fever that cannot be explained by a known illness. Some patients, especially the elderly, may not develop a fever. In these patients, the first signs of infection may be rapid breathing or mental confusion.

Diagnosis of a hospital-acquired infection is based on:

• symptoms and signs of infection
• examination of wounds and catheter entry sites
• review of procedures that might have led to infection
• laboratory test results

A complete physical examination is conducted in order to locate symptoms and signs of infection. Wounds and the skin where catheters have been placed are examined for redness, swelling, or the presence of pus or an abscess. The physician reviews the patient's record of procedures performed in the hospital to determine if any posed a risk for infection.

Laboratory tests are done to look for signs of infection. A complete blood count can reveal if the white blood cell count is high. White blood cells are immune system cells that increase in numbers in response to an infection. White blood cells or blood may be present in the urine when there is a UTI.

Cultures of blood, urine, sputum, other body fluids, or tissue are done to look for infectious microorganisms. If an infection is present, it is necessary to identify the microorganism so the patient can be treated with the correct medication. A sample of the fluid or tissue is placed in a special medium that bacteria will grow in. Other tests can also be done on blood and body fluids to look for and identify bacteria, fungi, viruses, or other microorganisms responsible for an infection.

If a patient has symptoms suggestive of pneumonia, a chest x ray is done to look for infiltrates of white blood cells and other inflammatory substances in the lung tissue. Samples of sputum can be studied with a microscope or cultured to look for bacteria or fungi.

Treatment

Once the source of the infection is identified, the patient is treated with antibiotics or other medication that kills the responsible microorganism. Many different antibiotics are available that are effective against different bacteria. Some common antibiotics are penicillin, cephalosporins, tetracyclines, and erythromycin. More and more commonly, some types of bacteria are becoming resistant to the standard antibiotic treatments. When this happens, a different, more powerful antibiotic must be used. Two strong antibiotics that have been effective against resistant bacteria are vancomycin and imipenem, although some bacteria are developing resistance to these antibiotics as well.

Fungal infections are treated with antifungal medications. Examples of these are amphotericin B, nystatin, ketoconazole, itraconazole, and fluconazole.

A number of antiviral drugs have been developed that slow the growth or reproduction of viruses. Acyclovir, ganciclovir, foscarnet, and amantadine are examples of antiviral medications.

Prognosis

Hospital-acquired infections are serious illnesses that cause death in about 1% of cases. Rapid diagnosis and identification of the responsible microorganism is necessary, so treatment can be started as soon as possible.

Prevention

Hospitals and other healthcare facilities have developed extensive infection control programs to prevent nosocomial infections. These programs focus on identifying high risk procedures and other possible sources of infection. High risk procedures such as urinary catheterization should be performed only when necessary and catheters should be left in for as little time as possible. Medical instruments and equipment must be properly sterilized to ensure they are not contaminated. Frequent handwashing by healthcare workers and visitors is necessary to avoid passing infectious microorganisms to hospitalized patients. In 2003, the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) announced it would make prevention of nosocomial infections a major goal in 2004 and the coming years. JCAHO, the body that inspects hospitals for quality and accredits them accordingly, issued an alert stating that hospital-acquired infections are seriously underreported. The problem has become more serious for hospitals to address as many bacteria are becoming resistant to antibiotics.

Antibiotics should be used only when necessary. Use of antibiotics creates favorable conditions for infection with the fungal organism Candida. Overuse of antibiotics is also responsible for the development of bacteria that are resistant to antibiotics.

KEY TERMS

Abscess— A localized pocket of pus at a site of infection.

Candida— A yeast-like fungal organism.

Catheter— A thin, hollow tube inserted into the body at specific points in order to inject or withdraw fluids from the body.

Generalized infection— An infection that has entered the bloodstream and has general systemic symptoms such as fever, chills, and low blood pressure.

Localized infection— An infection that is limited to a specific part of the body and has local symptoms.

Nosocomial infection— An infection acquired in the hospital.

Resources

PERIODICALS

Burke, John P. "Infection Control—A Problem for Patient Safety." The New England Journal of Medicine February 13, 2003: 651-656.

"Hospital-Acquired Infections are Being Underreported." RN March 2003: 16.

"Nosocomial Infection (From the Editor)." Health Care Food & Nutrition Focus June 2003: 2.

Hospital-acquired infections

Definition

A hospital-acquired infection, also called a nosocomial infection, is an infection that first appears between 48 hours and four days after a patient is admitted to a hospital or other health-care facility.

Description

About 5–10% of patients admitted to acute care hospitals and long-term care facilities in the United States develop a hospital-acquired, or nosocomial, infection, with an annual total of more than one million people. Hospital-acquired infections are usually related to a procedure or treatment used to diagnose or treat the patient's initial illness or injury. The Centers for Disease Control (CDC) of the U.S. Department of Health and Human Services has shown that about 36% of these infections are preventable through the adherence to strict guidelines by health care workers when caring for patients. What can make these infections so troublesome is that they occur in people whose health is already compromised by the condition for which they were first hospitalized.

Hospital-acquired infections can be caused by bacteria, viruses, fungi, or parasites. These microorganisms may already be present in the patient's body or may come from the environment, contaminated hospital equipment, health care workers, or other patients. Depending on the causal agents involved, an infection may start in any part of the body. A localized infection is limited to a specific part of the body and has local symptoms. For example, if a surgical wound in the abdomen becomes infected, the area around the wound becomes red, hot, and painful. A generalized infection is one that enters the bloodstream and causes systemic symptoms such as fever, chills, low blood pressure, or mental confusion. This can lead to sepsis, a serious, rapidly progressive multi-organ infection, sometimes called blood poisoning, that can result in death.

Hospital-acquired infections may develop from the performance of surgical procedures; from the insertion of catheters (tubes) into the urinary tract, nose, mouth, or blood vessels; or from material from the nose or mouth that is aspirated (inhaled) into the lungs. The most common types of hospital-acquired infections are urinary tract infections (UTIs), ventilator-associated pneumonia, and surgical wound infections. The University of Michigan Health System reports that the most common sources of infection in their hospital are urinary catheters, central venous (in the vein) catheters, and endotrachial tubes (tubes going through the mouth into the stomach). Catheters going into the body allow bacteria to walk along the outside of the tube into the body where they find their way into the bloodstream. A study in the journal Infection Control and Hospital Epidemiology shows that about 24% of patients with catheters will develop catheter related infections, of which 5.2% will become bloodstream infections. Death has been shown to occur in 4–20% of catheter-related infections.

Causes

All hospitalized patients are at risk of acquiring an infection from their treatment or surgery. Some patients are at greater risk than others, especially young children, the elderly, and persons with compromised immune systems. The National Nosocomial Infection Surveillance System database compiled by the CDC shows that the overall infection rate among children in intensive care is 6.1%, with the primary causes being venous catheters and ventilator-associated pneumonia. The risk factors for hospital-acquired infections in children include parenteral nutrition (tube or intravenous feeding), the use of antibiotics for more than 10 days, use of invasive devices, poor postoperative status, and immune system dysfunction. Other risk factors that increase the opportunity for hospitalized adults and children to acquire infections are:

• a prolonged hospital stay
• severity of underlying illness
• compromised nutritional or immune status
• use of indwelling catheters
• failure of health care workers to wash their hands between patients or before procedures
• prevalence of antibiotic-resistant bacteria from the overuse of antibiotics

Any type of invasive (enters the body) procedure can expose a patient to the possibility of infection. Some common procedures that increase the risk of hospital-acquired infections include:

• urinary bladder catheterization
• respiratory procedures such as intubation or mechanical ventilation
• surgery and the dressing or drainage of surgical wounds
• gastric drainage tubes into the stomach through the nose or mouth
• intravenous (IV) procedures for delivery of medication, transfusion , or nutrition

Urinary tract infection (UTI) is the most common type of hospital-acquired infection and has been shown to occur after urinary catheterization. Catheterization is the placement of a catheter through the urethra into the urinary bladder to empty urine from the bladder; or to deliver medication, relieve pressure, or measure urine in the bladder; or for other medical reasons. Normally, a healthy urinary bladder is sterile, with no harmful bacteria or other microorganisms present. Although bacteria may be in or around the urethra, they normally cannot enter the bladder. A catheter, however, can pick up bacteria from the urethra and give them an easy route into the bladder, causing infection. Bacteria from the intestinal tract are the most common type to cause UTIs. Patients with poorly functioning immune systems or who are taking antibiotics are also at increased risk for UTI caused by a fungus called Candida. The prolonged use of antibiotics, which may reduce the effectiveness of the patient's own immune system, has been shown to create favorable conditions for the growth of this fungal organism.

Pneumonia is the second most common type of hospital-acquired infection. Bacteria and other microorganisms are easily introduced into the throat by treatment procedures performed to treat respiratory illnesses. Patients with chronic obstructive lung disease, for example, are especially susceptible to infection because of frequent and prolonged antibiotic therapy and long-term mechanical ventilation used in their treatment. The infecting microorganisms can come from contaminated equipment or the hands of health care workers as procedures are conducted such as respiratory intubation, suctioning of material from the throat and mouth, and mechanical ventilation. Once introduced through the nose and mouth, microorganisms quickly colonize the throat area. This means that they grow and form a colony, but have not yet caused an infection. Once the throat is colonized, it is easy for a patient to aspirate the microorganisms into the lungs, where infection develops that leads to pneumonia.

Invasive surgical procedures increase a patient's risk of getting an infection by giving bacteria a route into normally sterile areas of the body. An infection can be acquired from contaminated surgical equipment or from the hands of health care workers. Following surgery, the surgical wound can become infected from contaminated dressings or the hands of health-care workers who change the dressing. Other wounds can also become easily infected, such as those caused by trauma, burns, or pressure sores that result from prolonged bed rest or wheel chair use.

Many hospitalized patients need continuous medications, transfusions, or nutrients delivered into their bloodstream. An intravenous (IV) catheter is placed in a vein and the medications, blood components, or liquid nutritionals are infused into the vein. Bacteria from the surroundings, contaminated equipment, or health care workers' hands can enter the body at the site of catheter insertion. A local infection may develop in the skin around the catheter. The bacteria can also enter the blood through the vein and cause a generalized infection. The longer a catheter is in place, the greater the risk of infection.

Other hospital procedures that may put patients at risk for nosocomial infection are gastrointestinal procedures, obstetric procedures, and kidney dialysis .

Symptoms

Fever is often the first sign of infection. Other symptoms and signs of infection are rapid breathing, mental confusion, low blood pressure, reduced urine output, and a high white blood cell count. Patients with a UTI may have pain when urinating and blood in the urine. Symptoms of pneumonia may include difficulty breathing and inability to cough. A localized infection begins with swelling, redness, and tenderness on the skin or around a surgical wound or other open wound, which can progress rapidly to the destruction of deeper layers of muscle tissue, and eventually sepsis.

Diagnosis

An infection is suspected any time a hospitalized patient develops a fever that cannot be explained by the underlying illness. Some patients, especially the elderly, may not develop a fever. In these patients, the first signs of infection may be rapid breathing or mental confusion.

Diagnosis of a hospital-acquired infection is determined by:

• evaluation of symptoms and signs of infection
• examination of wounds and catheter entry sites for redness, swelling, or the presence of pus or an abscess
• a complete physical examination and review of underlying illness
• laboratory tests, including complete blood count (CBC) especially to look for an increase in infectionfighting white cells; urinalysis , looking for white cells or evidence of blood in the urinary tract; cultures of the infected area, blood, sputum, urine, or other body fluids or tissue to find the causative organism
• chest x ray may be done when pneumonia is suspected to look for the presence of white blood cells and other inflammatory substances in lung tissue
• review of all procedures performed that might have led to infection

Treatment

Cultures of blood, urine, sputum, other body fluids, or tissue are especially important in order to identify the bacteria, fungi, virus, or other microorganism causing the infection. Once the organism has been identified, it will be tested again for sensitivity to a range of antibiotics so that the patient can be treated quickly and effectively with an appropriate medicine to which the causative organism will respond. While waiting for these test results, treatment may begin with common broad-spectrum antibiotics such as penicillin, cephalosporins , tetracyclines , or erythromycin. More and more often, some types of bacteria are becoming resistant to these standard antibiotic treatments, especially when patients with chronic illnesses are frequently given antibiotic therapy for long periods of time. When this happens, a different, more powerful, and more specific antibiotic must be used to which the specific organism has been shown to respond. Two strong antibiotics that have been effective against resistant bacteria are vancomycin and imipenem, although some bacteria are developing resistance to these antibiotics as well. The prolonged use of antibiotics is also known to reduce the effectiveness of the patient's own immune system, sometimes becoming a factor in the development of infection.

Fungal infections are treated with antifungal medications. Examples of these are amphotericin B, nystatin, ketoconazole, itraconazole, and fluconazole.

Viruses do not respond to antibiotics. A number of antiviral drugs have been developed that slow the growth or reproduction of viruses, such as acyclovir, ganciclovir, foscarnet, and amantadine.

Prevention

Hospitals take a variety of steps to prevent nosocomial infections, including:

• Adopt an infection control program such as the one sponsored by the U.S. Centers for Disease Control (CDC), which includes quality control of procedures known to lead to infection, and a monitoring program to track infection rates to see if they go up or down.
• Employ an infection control practitioner for every 200 beds.
• Identify high-risk procedures and other possible sources of infection.
• Strict adherence to hand-washing rules by health care workers and visitors to avoid passing infectious microorganisms to or between hospitalized patients.
• Strict attention to aseptic (sterile) technique in the performance of procedures, including use of sterile gowns, gloves, masks, and barriers.
• Sterilization of all reusable equipment such as ventilators, humidifiers, and any devices that come in contact with the respiratory tract.
• Frequent changing of dressings for wounds and use of antibacterial ointments under dressings.
• Remove nasogastric (nose to stomach) and endotracheal (mouth to stomach) tubes as soon as possible.
• Use of an antibacterial-coated venous catheter that destroys bacteria before they can get into the blood stream.
• Prevent contact between respiratory secretions and health care providers by using barriers and masks as needed.
• Use of silver alloy-coated urinary catheters that destroy bacteria before they can migrate up into the bladder.
• Limitations on the use and duration of high-risk procedures such as urinary catheterization.
• Isolation of patients with known infections.
• Sterilization of medical instruments and equipment to prevent contamination.
• Reductions in the general use of antibiotics to encourage better immune response in patients and reduce the cultivation of resistant bacteria.

Resources

books

Andreoli, T. E., J. C. Bennet, C. C. Carpenter, and F. Plum. Cecil Essentials of Medicine. Philadelphia: W.B. Saunders Co., 1997.

Schaffer, S. D., et al. Infection Prevention and Safe Practice. New York: Mosby-Year Book, 1996.

organizations

U.S. Center for Disease Control and Prevention (CDC). 1600 Clifton Road, Atlanta, GA 30333. 404-639-3311. <http://www.cdc.gov/health/disease.htm>.

other

"Safer Hospital Stay, and Reducing Hospital-Born Infections." Health Scout News, 2003 [cited July 7, 2003]. <http://www.healthscout.com>.

Toni Rizzo
L. Lee Culvert

NOSOCOMIAL INFECTIONS

A nosocomial, or hospital-acquired, infection is a new infection that develops in a patient during hospitalization. It is usually defined as an infection that is identified at least forty-eight to seventy-two hours following admission, so infections incubating, but not clinically apparent, at admission are excluded. With recent changes in health care delivery, the concept of "nosocomial infections" has sometimes been expanded to include other "health care–associated infections," including infections acquired in institutions other than acute-care facilities (e.g. nursing homes); infections acquired during hospitalization but not identified until after discharge; and infections acquired through outpatient care such as day surgery, dialysis, or home parenteral therapy.

Early studies reported at least 5 percent of patients became infected during hospitalization. With the increased use of invasive procedures, at least 8 percent of patients now acquire nosocomial infections.

The most frequent types of infection are urinary-tract infection, surgical-wound infection, pneumonia, and bloodstream infection (see Table 1). These infections follow interventions necessary for patient care, but which impair normal defenses. At least 80 percent of nosocomial urinary infections are attributable to the use of an indwelling urethral catheter. Surgical-wound infection follows interference with the skin barrier, and is associated with the intensity of bacterial contamination of the wound at surgery. Nosocomial pneumonia occurs most frequently in intensive-care-unit patients with endotracheal intubation on mechanical ventilation—the endotracheal tube bypasses normal defenses of the upper airway. Finally, primary nosocomial bloodstream infection occurs virtually only with the use of indwelling central vascular catheters, and correlates directly with the duration of catheterization.

Table 1

The clinical status of the patient is important in the development of infection. Many hospitalized patients, such as leukemia patients or transplant patients, have profoundly impaired immunity due to both their disease and therapy. These patients are highly susceptible to infection, frequently with organisms that do not cause infection in normal persons. Patients with neurologic problems may have swallowing difficulties due to aspiration of bacteria from the mouth or stomach, which can lead to pneumonia. Patients who have received antimicrobials may develop nosocomial infectious diarrhea caused by Clostridium difficile.

The hospital environment may also contribute to infections. Repeated outbreaks of Legionnaire's disease caused by organisms in a hospital's potable water or in air conditioning cooling towers have occurred. Increases in Aspergillus spores in the air during hospital construction cause fungal pneumonia in some immunocompromised patients, with a mortality rate of over 50 percent. Bacterial contamination of sterile intravenous fluids or equipment has repeatedly caused outbreaks of nosocomial infections. Finally, patients may acquire tuberculosis or chicken pox from other patients.

NATURE AND DIMENSION OF PUBLIC HEALTH PROBLEM

The high frequency of nosocomial infections places a substantial burden on individual patients and on the health care system. There is increased morbidity, including delayed wound healing, delayed rehabilitation, increased exposure to antimicrobial therapy and its potential adverse effects, and prolonged hospitalization. The average prolongation of stay is 3.8 days for urinary infection, 7.4 days for surgical-site infection, 5.9 days for pneumonia, and 7 to 24 days for primary bloodstream infection. Some infections, such as infection occurring in a hip or knee replacement, result in prolonged or even permanent disability and require repeated rehospitalization and reoperation. Nosocomial infections also cause mortality. The case-fatality rate for patients with ventilator-associated pneumonia is 42 percent, with an attributable mortality of 15 to 30 percent. For nosocomial bloodstream infection, the case fatality rate is 14 percent, with an estimated attributable mortality of 19 percent.

Nosocomial infections are costly. The direct costs of hospital-acquired infections in the United States is estimated to be $4.5 billion per year. In England, the cost for one health unit is estimated to be 3.6 million pounds per year. Prolongation of stay necessitated by nosocomial infection limits access of other patients to hospital resources, and contributes to overcrowding on wards and in emergency departments.

Nosocomial infections also contribute to the emergence and dissemination of antimicrobial-resistant organisms. Antimicrobial use for treatment or prevention of infections facilitates the emergence of resistant organisms. Patients with infection with antimicrobial-resistant organisms are then a source of infection for other hospitalized patients. Some bacteria, such as methicillin-resistant Staphylococcus aureus, may subsequently spread to the community.

CONTROL AND PREVENTION

Prevention of nosocomial infections requires a systematic, multidisciplinary approach. This is usually achieved under the leadership of an institutional infection-control program. The principle activities of such a program include surveillance, outbreak management, policy development, expert advice, and education. An optimal program may decrease the incidence of nosocomial infections by 30 to 50 percent.

Surveillance of nosocomial infections, by itself, may decrease the incidence. When each surgeon is provided with their own wound-infection rates and with other surgeons' rates for comparison, the institutional surgical-wound infection rate decreases. Outbreak control includes early identification of potential outbreaks, as well as evaluation and intervention if an outbreak is identified. Continuing education of hospital staff about the importance of, and their role in, preventing nosocomial infections is necessary. The infection-control program also provides expert consultation to other hospital programs such as occupational health, clinical microbiology, and pharmacy.

Institutional policies and practices must be developed and adhered to. In particular, optimal handwashing and glove use must be facilitated and reinforced, as transmission of organisms between patients occurs primarily on the hands of staff members. Isolation guidelines to identify and segregate patients who have an increased risk of transmitting infection to other patients or staff are also essential. Other important policies include: for urinary infection, the use and care of the indwelling catheter; and for surgical wound infection, optimal surgical technique including preoperative preparation and prophylactic antimicrobials. Many national or local standards and regulations will also prevent nosocomial infection, and institutions must be in compliance. These regulations cover hospital construction, municipal water supply, laundry management, food handling, waste disposal, sterilization and other reprocessing procedures, as well as standards for pharmacy and microbiology laboratory practice.

An effective infection-control program requires dedicated staff with appropriate training and sufficient resources. The number of personnel is determined by the size and complexity of the facility. Infection-control practitioners, usually from a nursing background, are responsible for program activity. In larger hospitals, program leadership is provided by a physician with training in epidemiology and infection control. Smaller facilities may obtain such expertise by contractual arrangement with outside experts. Oversight of the infection-control program is usually provided by a multidisciplinary infection-control committee. The program director, however, should report directly to senior hospital management to ensure optimal program effectiveness.

Lindsay E. Nicolle

(see also: Antisepsis and Sterilization; Barrier Nursing; Contagion; Hospital Administration )

Bibliography

Centers for Disease Control and Prevention (1999). "Guidelines for Prevention of Surgical Site Infection." Infection Control and Hospital Epidemiology 20:247–278.

Health Canada Laboratory Centre for Disease Control (1998). "Handwashing, Cleaning, Disinfection, and Sterilization in Health Care." Canadian Communicable Disease Report 24S8(Supp.).

—— (1999). "Routine Practices and Additional Precautions for Preventing Transmission of Infection in Health Care." Canadian Communicable Disease Report 25S4(Supp.).

Mayhall, C. G., ed. (1999). Hospital Epidemiology and Infection Control, 2nd edition. Philadelphia, PA: Lippincott Williams and Wilkins.

Scheckler, W. E.; Brumhall, D.; Buck, A. S.; Farr, B. M.; Friedman, C.; Garibaldi, R. A.; Gross, P. A.; Harris, J. A.; Hierholzer, W. J., Jr.; Martone, W. J.; McDonald, L. L.; Solomon, S. L. (1998). "Requirements for Infrastructure and Essential Activities of Infection Control and Epidemiology in Hospitals: A Consensus Panel Report." Infection Control and Hospital Epidemiology 19:114–124.

Shlaes, D. M.; Gerding, D. N.; John, J. F.; Craig, W. A.; Bornstein, D. L.; Duncan, R. A.; Eckman, M. R.; Farrer, W. E.; Greene, W. H.; Lorian, V.; Levy, S.; McGowan, J. E.; Paul, S. M.; Ruskin, J.; Tenover, F. C.; and Watanakunakorn, C. (1997). "Society for Healthcare Epidemiology of America and Infectious Diseases Society of America Joint Committee on the Prevention of Antimicrobial Resistance: Guidelines for the Prevention of Antimicrobial Resistance in Hospitals." Infection Control and Hospital Epidemiology 18:275–291.

Nosocomial infections

A nosocomial infection is an infection that is acquired in a hospital. More precisely, the Centers for Disease Control in Atlanta, Georgia, defines a nosocomial infection as a localized infection or one that is widely spread throughout the body that results from an adverse reaction to an infectious microorganism or toxin that was not present at the time of admission to the hospital.

The term nosocomial infection derives from the nosos, which is the Greek word for disease.

Nosocomial infections have been a part of hospital care as long as there have been hospitals. The connection between the high death rate of hospitalized patients and the exposure of patients to infectious microorganisms was first made in the mid-nineteenth century. Hungarian physician Ignaz Semmelweis (1818–1865) noted the high rate of death from puerperal fever in women who delivered babies at the Vienna General Hospital. Moreover, the high death rate was confined to a ward at which medical residents were present. Another ward, staffed only by midwives who did not interact with other areas of the hospital, had a much lower death rate. When the residents were made to wash their hands in a disinfectant solution prior to entering the ward, the death rate declined dramatically.

At about the same time, the British surgeon Joseph Lister (1827–1912) also recognized the importance of hygienic conditions in the operating theatre. His use of phenolic solutions as sprays over surgical wounds helped lessen the spread of microorganisms resident in the hospital to the patient. Lister also required surgeons to wear rubber gloves and freshly laundered operating gowns for surgery. He recognized that infections could be transferred from the surgeon to the patient. Lister's actions spurred a series of steps over the next century, which has culminated in today's observance of sterile or near-sterile conditions in the operating theatre.

Despite these improvements in hospital hygienic practices, the chance of acquiring a nosocomial infection still approaches about 10%. Certain hospital situations are even riskier. For example, the chance of acquiring a urinary tract infection increases by 10% for each day a patient is equipped with a urinary catheter. The catheter provides a ready route for the movement of bacteria from the outside environment to the urinary tract.

The most common microbiological cause of nosocomial infection is bacteria. The microbes often include both Gramnegative and Gram-positive bacteria. Of the Gram-negative bacteria, Escherichia coli, Proteus mirabilis, and other members of the family known as Enterobacteriacaea are predominant. These bacteria are residents of the intestinal tract. They are spread via fecal contamination of people, instruments or other surfaces. Other Gram-negative bacteria of consequence include members of the genera Pseudomonas and Acinetobacter.

Gram-positive bacteria, especially Staphylococcus aureus, frequently cause infections of wounds. This bacterium is part of the normal flora on the surface of the skin, and so can readily gain access to a wound or surgical incision.

One obvious cause of nosocomial infections is the state of the people who require the services of a hospital. Often people are ill with ailments that adversely affect the ability of their immune systems to recognize or combat infections. These people are more vulnerable to disease than they would otherwise be. A hospital is a place where, by its nature, infectious microorganisms are encountered more often than in other environments, such as the home or workplace. Simply by being in a hospital, a person is exposed to potentially diseasecausing microorganisms.

A compounding factor, and one that is the cause of many nosocomial infections, is the developing resistance of bacteria to a number of antibiotics in common use in hospitals. For example, strains of Staphylococcus aureus that are resistant to all but a few conventional antibiotics are encountered in hospitals so frequently as to be almost routine. Indeed, many hospitals now have contingency plans to deal with outbreaks of these infections, which involve the isolation of patients, disinfection of affected wards, and monitoring of other areas of the hospital for the bacteria. As another example, a type of bacteria known as enterococci has developed resistance to virtually all antibiotics available. Ominously, the genetic determinant for the multiple antibiotic resistance in enterococci has been transferred to Staphylococcus aureus in the laboratory setting. Were such genetic transfer to occur in the hospital setting, conventional antibiotic therapy for Staphylococcus aureus infections would become virtually impossible.

See also Bacteria and bacterial infection; History of public health; History of the development of antibiotics