When would a Covid-19 (Coronavirus disease 2019) test indicate infection in a person exposed to someone with Covid-19 during the 7 days after the infected person's day 1 of infection?

Optimal Testing Timing After COVID-19 Exposure

For a person exposed to someone with COVID-19 during days 1-7 of their infection, testing should be performed at least 5 days after the exposure to reliably detect infection. 1, 2

Testing Timeline Algorithm

Days 0-4 Post-Exposure

• Do not test yet unless symptoms develop, as testing during this window has poor sensitivity and high false-negative rates 1, 2
• If any symptoms appear before day 5 (fever, cough, shortness of breath, fatigue, muscle aches, headache, loss of taste/smell, sore throat, congestion, nausea, vomiting, or diarrhea), the exposed person should be tested immediately regardless of timing 1, 2
• Monitor daily for symptom development and practice isolation/quarantine measures 2

Day 5 Post-Exposure (Optimal Testing Window)

• Perform SARS-CoV-2 molecular testing (NAAT) on day 5 after the last exposure 1, 2
• This timing accounts for the median incubation period of approximately 5 days (range 1-14 days, with 97.5% developing symptoms within 11.5 days) 1, 3
• Acceptable specimen types include nasopharyngeal swab, midturbinate swab, anterior nares plus oropharyngeal swab, saliva, or mouth gargle 1, 2

After Day 5

• If test is negative on day 5: Repeat testing is generally not recommended unless new symptoms develop 1, 2
• Continue monitoring for symptoms through day 14 post-exposure 1, 2
• If test is positive: Initiate isolation protocols immediately 2

Critical Rationale for the 5-Day Window

The Infectious Diseases Society of America (IDSA) specifically recommends waiting at least 5 days after exposure based on moderate certainty evidence, as this timing optimizes test sensitivity by allowing sufficient viral replication to reach detectable levels 1, 2. Testing earlier than day 5 significantly increases the risk of false-negative results because viral loads may not yet be high enough for detection 2.

Important Caveats

• Definition of exposure: Close contact is defined as at least 15 minutes over a 24-hour period with someone who has laboratory-confirmed COVID-19 1, 2
• Quarantine duration: The CDC recommends a 14-day quarantine period after last contact, though this can be shortened to 10 days without testing or 7 days with appropriately timed negative testing 1
• Asymptomatic transmission risk: Asymptomatic and presymptomatic individuals can transmit SARS-CoV-2, making testing and isolation important even without symptoms 1, 4
• Single negative test limitations: One negative test is inadequate to rule out infection, particularly if performed too early or if specimen collection was poor 1