When should a rapid strep test be performed after exposure to streptococcal infection?

Timing of Rapid Strep Test After Exposure

Test at least 5 days after exposure to someone with streptococcal pharyngitis, or immediately if symptoms develop before 5 days. 1

Testing Algorithm Based on Symptom Status

Asymptomatic Exposure Without Symptoms

• Do not test asymptomatic household contacts of patients with Group A streptococcal pharyngitis, as routine testing or treatment of contacts is not recommended. 2
• If you must test an exposed asymptomatic individual (such as for specific high-risk situations), wait at least 5 days post-exposure before testing. 1
• The incubation period for Group A streptococcus is typically 2-5 days, so testing earlier than this window may yield false-negative results even if infection is developing. 3, 4

Symptomatic After Exposure

• Test immediately when symptoms develop, regardless of how many days have passed since exposure. 1, 2
• Use rapid antigen detection test (RADT) when clinical features suggest possible streptococcal pharyngitis, including sudden onset of sore throat, fever, headache, tonsillar exudate, or tender anterior cervical lymphadenopathy. 2, 5
• The RADT has excellent specificity (≥95%), meaning a positive result allows confident treatment decisions without culture confirmation. 1

Important Testing Considerations

Age-Specific Backup Testing Requirements

• Children and adolescents (3-18 years): Always perform backup throat culture if RADT is negative, as the 80-90% sensitivity means false-negatives can occur in truly infected patients. 1, 2
• Adults: Backup culture after negative RADT is generally not necessary due to lower incidence of streptococcal pharyngitis and rare occurrence of rheumatic fever complications. 2

Common Pitfalls to Avoid

• Do not test children under 3 years unless specific risk factors exist (such as an older sibling with confirmed Group A streptococcus infection), as incidence is low and rheumatic fever is rare in this age group. 2
• Avoid testing when overt viral features are present, including conjunctivitis, coryza, cough, diarrhea, or hoarseness, as these strongly suggest viral etiology. 2, 5
• Never use antistreptococcal antibody titers for diagnosis of acute pharyngitis, as they reflect past infections rather than current disease. 2
• False-negative results can occur if the patient received antibiotics shortly before or at the time of specimen collection, so document any recent antibiotic use. 2

Clinical Decision Support

Use the Centor criteria to determine testing necessity: 1, 5

• Fever
• Tonsillar exudate
• Tender anterior cervical lymphadenopathy
• Absence of cough

Test patients with 3-4 Centor criteria; those with 0-2 criteria are unlikely to have streptococcal infection and testing may lead to unnecessary antibiotic use. 1, 2