From the Guidelines
Yes, it is possible to get a negative Group A Streptococcus (GAS) test result while still having streptococcal infection. According to the most recent and highest quality study 1, rapid strep tests have a sensitivity of about 70-90%, meaning they can miss 10-30% of actual strep infections. False negatives can occur due to improper specimen collection, testing too early or late in the illness, prior antibiotic use, or low bacterial load.
Clinical Considerations
If strep throat is strongly suspected despite a negative rapid test, healthcare providers often send a throat culture, which is more accurate but takes 24-48 hours for results. The Infectious Diseases Society of America recommends that in children and adolescents, negative RADT tests should be backed up by a throat culture 1.
Treatment Approach
In cases with high clinical suspicion (fever, tonsillar exudates, tender lymph nodes, absence of cough), a doctor might treat empirically with antibiotics like penicillin V (250-500 mg twice daily for 10 days), amoxicillin (500 mg twice daily for 10 days), or azithromycin (500 mg on day 1, then 250 mg daily for 4 days) for penicillin-allergic patients, as suggested by the clinical practice guideline for the diagnosis and management of group A streptococcal pharyngitis 1. This approach helps prevent complications like rheumatic fever and reduces symptom duration and contagiousness.
Key Points to Consider
- The clinical features alone do not reliably discriminate between GAS and viral pharyngitis except when overt viral features like rhinorrhea, cough, oral ulcers, and/or hoarseness are present 1.
- Routine use of back-up throat cultures for those with a negative RADT is not necessary for adults in usual circumstances, because of the low incidence of GAS pharyngitis in adults and because the risk of subsequent acute rheumatic fever is generally exceptionally low in adults with acute pharyngitis 1.
- Anti-streptococcal antibody titers are not recommended in the routine diagnosis of acute pharyngitis as they reflect past but not current events 1.
From the Research
GAS Negative Results and Streptococcus
- It is possible to get GAS negative results and still have streptococcus, as the sensitivity of rapid antigen tests is not 100% 2.
- A negative rapid antigen test result does not completely rule out the presence of group A beta-hemolytic streptococcal pharyngitis, especially in children and adolescents 2.
- In such cases, a throat culture is recommended to confirm the diagnosis 3, 2.
Diagnostic Tests
- Throat culture is considered the gold standard for diagnosing GAS pharyngitis 3.
- Rapid antigen tests are commonly used for initial screening, but may not always detect the presence of streptococcus 2.
- Clinical decision rules, such as assessing fever, tonsillar exudate, cervical lymphadenitis, and patient age, can help increase the suspicion of group A beta-hemolytic streptococcal infection 2.
Treatment and Management
- Penicillin and amoxicillin are first-line antibiotics for treating GAS pharyngitis, with a recommended course of 10 days 2, 4, 5.
- Other antibiotics, such as cephalosporins and macrolides, may also be effective, but the evidence is uncertain 4.
- Treatment should be guided by clinical judgment and patient factors, such as allergy history and medication tolerance 4.