Is it best practice to culture every sore throat in patients who test negative for streptococcal (strep) infection via a rapid antigen test?

Backup Culture After Negative Rapid Strep Test

In children and adolescents, you must obtain a backup throat culture after every negative rapid antigen detection test (RADT), but in adults, a negative RADT alone is sufficient to rule out streptococcal pharyngitis without further testing. 1, 2

Age-Based Testing Algorithm

Children and Adolescents (Ages 3-18 Years)

• Always perform backup throat culture after negative RADT because rapid tests have only 80-90% sensitivity, meaning they miss 10-20% of true streptococcal infections 1, 2, 3
• The IDSA gives this recommendation a "strong" rating with "high" quality evidence 1
• Treatment can be safely delayed until culture results return—initiating antibiotics within 9 days of symptom onset still effectively prevents acute rheumatic fever 2, 4
• The higher prevalence of group A streptococcal pharyngitis in this age group (20-30%) and the risk of rheumatic fever justify the backup culture approach 1, 4

Adults

• Do not routinely perform backup throat cultures after negative RADT—the negative test alone is sufficient to withhold antibiotics 1, 2, 4
• The IDSA gives this recommendation a "strong" rating with "moderate" quality evidence 1
• Adults have only 5-10% prevalence of streptococcal pharyngitis and exceptionally low risk of acute rheumatic fever 2, 4
• The RADT has ≥95% specificity, making false positives rare 2, 3, 4

Rationale for Age-Based Differences

The divergent recommendations reflect different risk-benefit calculations:

• In children: The combination of higher disease prevalence, greater risk of rheumatic fever, and the test's 10-20% false-negative rate creates unacceptable risk of missing true infections 1, 2
• In adults: The low disease prevalence (5-10%) and near-zero rheumatic fever risk mean that the small number of missed cases does not justify the cost and antibiotic overuse from backup cultures 1, 2, 4

Important Caveats

When Adults May Need Backup Culture

• Physicians who wish to achieve maximal diagnostic sensitivity may continue using backup cultures or conventional throat culture alone 1
• Special circumstances such as outbreak settings or high-risk populations may warrant backup testing 1

When NOT to Test at All

• Do not test children under 3 years old except when an older sibling has confirmed streptococcal infection—acute rheumatic fever is rare in this age group 1, 3, 4
• Do not test patients with clear viral features such as cough, rhinorrhea, hoarseness, conjunctivitis, or oral ulcers—these strongly suggest viral etiology 1, 3

Positive RADT Results

• Never perform backup culture after positive RADT regardless of age—the test's high specificity (≥95%) makes false positives extremely rare, allowing confident treatment decisions 1, 3

Common Pitfalls to Avoid

• Do not assume proper swabbing technique—specimens must be obtained from both tonsillar surfaces and the posterior pharyngeal wall to maximize sensitivity 3, 4
• Do not retest asymptomatic household contacts—screening or prophylactic treatment of contacts is not recommended 1, 4
• Recent antibiotic use can cause false-negative results if antibiotics were given shortly before specimen collection 3