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Types of Strep Infections

author image Dr. Tina M. St. John
Tina M. St. John runs a health communications and consulting firm. She is also an author and editor, and was formerly a senior medical officer with the U.S. Centers for Disease Control and Prevention. St. John holds an M.D. from Emory University School of Medicine.
Types of Strep Infections
Laboratory testing enables health care professionals to differentiate between the various kinds of strep bacteria.

Streptococcal bacteria are a major cause of disease. Different kinds of strep, including Streptococcus pneumoniae, group A Streptococcus and group B Streptococcus, demonstrate differing affinities for various body sites. Strep infections range from mild to potentially life-threatening. Early diagnosis and treatment decrease the risk for serious complications associated with strep infections.

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Streptococcus Pneumoniae

Streptococcus pneumoniae, also known as S. pneumoniae and pneumococcus, is a common cause of bacterial infection. The medical reference text, “Principles and Practice of Infectious Diseases” notes that pneumococcus commonly causes pneumonia, sinusitis, meningitis and middle ear infections. Other infections potentially caused by S. pneumoniae include endocarditis, an infection of the heart; septic arthritis, a joint infection; osteomyelitis, infection of the bone; cellulitis, a deep skin infection; and peritonitis, infection of the abdominal cavity. Pneumococcal bacteria possess capsules that surround the bacteria. The capsule interferes with phagocytosis, an immune system response involving the ingestion and killing of invading bacteria. Evasion of this important immune system defense enables the tissue invasion required to cause infection. Pneumococcal vaccines markedly decrease the risk of S. pneumoniae infections.

Group A Streptococcus

Group A streptococcus bacteria, also known as Streptococcus pyogenes, commonly colonize the skin and throat. Colonization is a carrier state wherein the bacteria inhabit a site without causing disease. However, subtle changes in a carrier’s health status may shift conditions sufficiently for colonizing bacteria to invade and cause disease. The Centers for Disease Control and Prevention reports that common group A strep infections include strep throat and impetigo, a superficial skin infection. Group A strep also cause deeper skin infections, including cellulitis and erysipelas. Necrotizing fasciitis, or streptococcal gangrene, is the most serious of the group A strep skin infections. This rapidly progressive infection spreads from the skin to the underlying tissues, causing widespread tissue death. Tissue destruction can lead to significant disfigurement or amputation. Dr. Kenneth Todar notes in “Todar’s Online Textbook of Bacteriology” that other infections caused by group A strep include tonsillitis, middle ear infections, sinusitis, pneumonia, septic arthritis, osteomyelitis, meningitis, endocarditis and myositis--a muscle infection.

Group B Streptococcus

Group B Streptococcus, also known as Streptococcus agalactiae, is an important cause of infection in newborns and pregnant women. The bacteria commonly colonize the female rectum and vagina. During pregnancy, the bacteria may invade the pregnancy-related tissues. Both the pregnant woman and her baby may be infected. Dr. Christina Phares and colleagues report in a 2008 article published in “The Journal of the American Medical Association” that approximately 50 percent of pregnancies associated with group B strep infection of the reproductive organs or pregnancy-related tissues result in fetal death. In addition to infection during pregnancy, babies may contract group B strep during the delivery process, potentially leading to bloodstream infection, meningitis or pneumonia.

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