Streptococcal Infections, Group A
Streptococcal Infections, Group A
Disease History, Characteristics, and Transmission
Introduction
Group A Streptococcus bacteria (also called group A streptococci or GAS for short) can cause many diseases. The species Streptococcus pyogenes (pronounced pie-AHJ-uh-neez) is the group A Streptococcus that causes most disease in humans and is often treated as synonymous with GAS, though there are also non-S. pyogenes group A streptococci. Among the diseases caused by GAS are scarlet fever, strep throat, toxic shock syndrome, and impetigo. GAS were often life-threatening before the discovery and mass-production of antibiotics. Untreated GAS infections also threaten health by triggering autoimmune diseases, including glomerulonephritis and rheumatic fever. Rheumatic fever is life-threatening, killing from 2% to 5% of patients.
Some invasive GAS infections that invade the lungs, blood, or deep muscle and fat tissue are life threatening. Most invasive GAS illnesses have a mortality rate of 10– 15%. Necrotizing fasciitis (also called “flesh-eating disease”) and streptococcal toxic shock syndrome (STSS) are two of the least common, but most severe and aggressive forms of invasive GAS. Approximately 20% of patients with necrotizing fasciitis die, while STSS has a mortality rate of 60%.
Today, most routine GAS infections are routinely treated with antibiotics in industrialized countries, but resistance to earlier-developed antibiotics is an increasing problem. In the developing world, untreated GAS and its resultant autoimmune diseases are still a widespread problem.
Disease History, Characteristics, and Transmission
The streptococci bacteria were first described by German-Austrian physician Christian Theodor Billroth (1829–1894), who found Streptococcus pyogenes growing in infected wounds (the word “pyogenes” is from the Greek for “pus-forming”). S. pyogenes was actually named by German physician Michael Josef Rossbach (1842–94) in 1884, but was not termed a group A streptococcus until the 1930s, when American scientist Rebecca Lancefield (1895–1981) classed the streptococci into the alphabetically labeled groups that are still called Lancefield groups. Lancefield also established that a protein embedded in the cell wall of group A streptococci, M protein, is crucial to their power to cause disease. There are over 120 varieties of S. pyogenes, distinguished by their varying M proteins.
The streptococci are gram-positive bacteria that tend to grow in chains or pairs. They are classed into two basic groups based on their ability to break down blood cells under laboratory conditions, a process called hemolysis (hemo meaning blood, and lysis meaning breakup). The beta-hemolytic streptococci break up blood cells completely, creating clear areas around bacteria colonies growing on blood agar in petri dishes. (Petri dishes are small, round, shallow dishes used commonly in laboratories to grow microorganisms; agar is a form of jelly derived from seaweed or algae, chemically a sugar; and blood agar is agar mixed with blood cells, usually from horses or sheep.)
Further division of the beta-hemolytic streptococci into the Lancefield groups A to T is based on the chemical makeup of the cell wall. The group A streptococci, of which S. pyogenes is the most important, are globular and about 0.6 to 1 mm in diameter. These bacteria primarily invade human epithelial cells, which constitute the skin and line the respiratory and digestive tracts.
Strep throat is an infection of the throat with S. pyogenes. About 18 or 20 days after the end of a strep throat infection, acute rheumatic fever may occur. The primary symptom of rheumatic fever is pain in the joints. Inflammation of the heart may also occur, causing permanent damage to one or more heart valves. Post-streptococcal glomerulonephritis—inflammation of the kidney—may also develop about 10 days after a GAS infection.
WORDS TO KNOW
GLOMERULONEPHRITIS: Glomerulonephritis is inflammation of the kidneys. Mostly it affects the glomeruli, the small capsules in the kidney where blood flowing through capillaries transfers body wastes to urine.
IMPETIGO: Impetigo refers to a very localized bacterial infection of the skin. It tends to afflict primarily children, but can occur in people of any age. Impetigo caused by the bacteria Staphylococcus aureus (or staph) affects children of all ages, while impetigo caused by the bacteria called group A streptococci (Streptoccus pyogenes or strep) are most common in children ages two to five years.
PUERPERAL FEVER: Puerperal fever is a bacterial infection present in the blood (septicemia) that follows childbirth. The Latin word puer, meaning boy or child, is the root of this term. Puerperal fever was much more common before the advent of modern hygiene practices, but infections still occur. Louis Pasteur proved that puerperal fever is caused by Streptococcus bacteria, which is now treated with antibiotics.
Transmission of S. pyogenes is via direct contact with mucus, saliva, and open sores, or through airborne saliva droplets released by sneezing or coughing.
Severe, invasive GAS infections are rare among otherwise healthy individuals. Invasive GAS infections are most likely to occur in persons with diabetes or weakened immune systems, persons who use steroids or some other medications, or in patients with recent trauma or surgical wounds.
Scope and Distribution
The only known reservoir for S. pyogenes is human beings. About 5% to 15% of health persons harbor S. pyogenes, usually in their upper respiratory tract, without any sign of infection. This bacterium is one of the most common causes of bacterial infection in human beings, and in many developed nations is the most common cause of bacterial infection of the upper respiratory tract for all age groups.
IN CONTEXT: TRENDS AND STATISTICS
Streptococcal pharyngitis (strep throat) is one of the most common childhood illnesses worldwide. In industrialized countries, thanks to antibiotic treatment of strep throat, rheumatic fever has an annual incidence of around 0.5 cases per 100,000 school-age children. In developing countries, however, the annual incidence of rheumatic fever ranges from 100 to 200 cases per 100,000 school-aged children—from 200 to 400 times higher than the developed-world rate. There are over 18 million cases of severe GAS disease such as rheumatic heart disease worldwide, with more than half a million deaths per year.
In the eighteenth and nineteenth centuries, scarlet fever was a major killer, and until antibiotics were available to treat GAS infections, rheumatic fever (usually following strep throat) was a widespread childhood disease. Moreover, puerperal fever was common in maternity wards, where sanitation was poor (the role of bacteria in causing infection was not yet known) and S. pyogenes was transmitted by doctors’ unwashed hands. During childbirth, S. pyogenes would often infect the mother's bloodstream through tears in the vaginal wall or skin of the genital area. This commonly resulted in death rates in maternity wards of about 10% to 25%, with occasional epidemics leading to much higher death rates. Today, puerperal fever is rare in industrialized countries because of standardized medical hygiene and prevalent antibiotics.
Treatment and Prevention
For over a century, attempts have been made to develop a GAS vaccine. As of early 2007, one GAS vaccine was in phase 2 clinical human trials, with several others approaching the human trial phase. However, no GAS vaccine was yet available.
Prevention of GAS infections consists primarily of handwashing, sterilization in health-care environments, and avoiding contact with infected persons. According to the World Health Organization (WHO), the only effective and cost-effective large-scale control strategy for GAS diseases, apart from health education and medical hygiene, is treatment by antibiotics.
Impacts and Issues
WHO estimates that puerperal sepsis, infection of women giving birth, by GAS accounts for 15% of maternal deaths globally today. Most of these deaths occur in developing countries where sterile conditions and anti-biotics are more rare.
Failure of penicillin to eradicate GAS from the throat has been reported with increasing frequency in recent years. Whether antibiotics other than penicillin should be added to standard treatment regimens for strep throat and other GAS infections is debated among physicians. Treating resistant infections requires more powerful and recently-developed antibiotics. However, many physicians worry that prescribing newer, more powerful antibiotics as a first course of treatment may encourage further anti-biotic resistance in GAS infections.
See AlsoImpetigo; Necrotizing Fasciitis; Puerperal Fever; Scarlet Fever; Streptococcal Infections, Group B.
BIBLIOGRAPHY
Books
Smith, Tara and Edward Alcamo. Streptococcus (Group A) (Deadly Diseases and Epidemics). Philadelphia, PA: Chelsea House Publications, 2004.
Periodicals
Cunningham, Madeleine W. “Pathogenesis of Group A Streptococcal Infections.” Clinical Microbiology Reviews. 13 (2000): 470-511.
Facklam, Richard. “What Happened to the Streptococci: Overview of Taxonomic and Nomenclature Changes.” Clinical Microbiology Reviews.15 (2002): 613-630.
Kaplan, Edward L., et al. “Reduced Ability of Penicillin to Eradicate Ingested Group A Streptococci from Epithelial Cells: Clinical and Pathogenic Implications.” Clinical Infectious Diseases.43 (2006): 1398–1406.
Web Sites
World Health Organization (United Nations).“A Review of the Technical Basis for the Control of Associated with Group A Streptococcal Infections.” 2005 <http://www.who.int/child-adolescent-health/New_Publications/CHILD_HEALTH/DP/WHO_FCH_CAH_05.08.pdf> (accessed February 2, 2007).