Group A Streptococcus Infections

  • Medical Author:
    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

  • Medical Editor: Melissa Conrad Stöppler, MD
    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD

    Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

How are group A streptococcal (GAS) infections diagnosed?

After a history and physical examination, many clinicians presumptively diagnose strep throat from its symptom production and throat appearance (see Fig. 2). However, cultures from the throat or other site of infection form the basis of definitive testing. For example, GAS organisms will grow on sheep blood agar plates that contain two different antibiotics and cause beta hemolysis (complete sheep blood red cell lysis to form a clear area) of the sheep red blood cells (see Fig. 3). In addition, there are rapid tests (RADT or rapid antigen detection test) that take only a few minutes to complete that detect a carbohydrate surface antigen produced by GAS, with specificity of about 95% or better and fairly good sensitivity of about 80%-90%.

Because there are many other groups of Streptococcus spp., positive identification of the infecting bacteria is necessary to separate out other bacteria that may cause some similar symptoms but may require a different workup, different treatment, and produce different complications.

Image of beta hemolysis.
Figure 4: Image of beta hemolysis. SOURCE: CDC/Richard R. Facklam, PhD

These tests help distinguish GAS from Streptococcus pneumoniae and other organisms.

What is the treatment for invasive group A streptococcal disease?

Antibiotics treat invasive GAS infections as well as noninvasive GAS infections. Although many antibiotics may be adequate treatment for GAS infections, the best practice methods would be to determine antibiotic sensitivity of GAS bacteria to be sure the bacteria are susceptible to the antibiotics. Milder infections caused by GAS (strep throat, skin infections) are often treated with oral antibiotics (for example, penicillin v [Pen-Vee-K, Veetids], amoxicillin [Amoxil, Dispermox, Trimox], cephalosporins; if allergic to penicillins, erythromycin [E-Mycin, Eryc, Ery-Tab, Pce, Pediazole, Ilosone], azithromycin [Zithromax, Zmax]). Some third-generation cephalosporins (for example, ceftriaxone [Rocephin]), given IV or IM, followed by oral antibiotics are useful to treat mild to moderate infections. However, invasive GAS infections require a more aggressive treatment approach. High doses of penicillin, together with clindamycin (Cleocin) by sequential IV administration, are often recommended. Some investigators suggest adding immune globulin to the multi-antibiotic treatment.

In addition to antibiotics, surgical intervention may be necessary to remove dead and dying tissue to limit the spread of invasive GAS organisms. This is almost always done in patients who develop necrotizing fasciitis. In addition, early diagnosis and treatment of invasive GAS infections yield the best patient outcomes. Many clinicians consult with an infectious-disease specialist to help determine the best antibiotic therapy for individual patients. More GAS strains are being reported to have some resistance to one or more antibiotics so the treatment may require alterations in antibiotics. The infectious-disease specialist can help choose the most effective antibiotic combinations to treat antibiotic-resistant GAS organisms.

Medically Reviewed by a Doctor on 2/19/2016
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