Conditions Where Lab Tests for Group A Beta-Hemolytic Streptococci  are Not Available or Not Practical

• Antibiotics will not be needed for every patient that presents w/ sore throat
• Antibiotics should not be withheld if the clinical condition is severe or group A beta-hemolytic streptococci  is suspected
• Modified Centor score can be used to decide on which patients need no testing, lab tests (throat swab or RADT) or empiric antibiotic therapy
  • Score of 0 to 1 does not require testing or antibiotic therapy
  • Patients w/ score of 2 or 3 require testing, positive results warrant empiric therapy
  • Score of ≥4 is at high risk of group A beta-hemolytic streptococci  & empiric therapy is considered

Who Should be Tested for Group A Beta-Hemolytic Streptococci  Pharyngitis?

• Clinical presentation of group A beta-hemolytic streptococci  & viral pharyngitis greatly overlap
• Patients who have clinical & epidemiological findings suggestive of group A beta-hemolytic streptococci  pharyngitis should be tested for the presence of group A streptococci in the pharynx
• Diagnostic testing of contacts of infected patients is not routinely recommended

Throat Swab Culture

• Gold standard for confirmation of clinical diagnosis of group A beta-hemolytic streptococci  pharyngitis
• If done correctly, culture of a single throat swab on a blood agar plate has a sensitivity of 90-95%
• Less expensive than RADT & more readily available
• Results take 24-48 hours
• Does not differentiate between illness and carrier states
• False-negative results may be seen in patients who have received antibiotic therapy shortly before or at the time the swab was obtained

Proper Technique of Obtaining a Throat Swab

• Swab the surface of both the tonsils, tonsillar fossae and posterior pharyngeal wall
• Do not include the mouth, uvula and oropharynx
• Optimally done at onset of symptoms and before antimicrobial therapy is started

Rapid Antigen Detection Test (RADT)

• Developed for the identification of group A beta-hemolytic streptococci  directly from throat swabs
• More expensive than throat swab cultures, but results are available faster (within minutes)
• With sensitivity of 80-90% & specificity of 90-99%
• Does not differentiate between illness & carrier states
• A rapid test can lead to earlier initiation of definitive therapy with the following advantages:
  • Reduced risk of spread of group A beta-hemolytic streptococci 
  • Reduced acute morbidity associated with illness
  • Earlier return of patient to work or school

• A negative RADT result for an adult patient does not need to be confirmed with a throat culture because of the low incidence of streptococcal infection and low risk of rheumatic fever in this age group