Question: If I think I may have been exposed to COVID, how long should I wait to get tested?

Answer: We’ve talked a bit about this in previous posts (see Q&A of 9/18 #Antigen Tests, Q&A of 7/12 #Timeline, and Q&A of 7/3 #False Negative). Based on what I’ve read,the best time to get tested is as soon as you feel symptoms OR 3–5 days after exposure (if you aren’t experiencing symptoms). Here’s a quick synthesis:

Timeline: The median time of symptom onset is 5 days after exposure (range: 2–14 days). People can transmit the virus before showing symptoms, as early as 2 days after exposure. Yesterday CDC updated its “close contact” definition, which is now “anyone who was within 6 feet of an infected person for a total of 15 minutes or more [over a 24-hour period].” If you have reason to believe you were exposed (e.g. in close contact), please self-quarantine, and if possible, get tested.

Testing: Three things we can be confident about and one thing we’re less confident about:

1) If you test the day of exposure, you’re sure to get a negative result, even if the virus has begun circulating in your body.

2) If you test the day of symptom onset and you are infected with SARS-CoV-2, you’re very likely to get a positive result.

3) If you test several days after symptom onset, it’s better to use a PCR test rather than an antigen test; when using a PCR test you’re also very likely to get a positive result if you are indeed infected.

4) If you are pre-symptomatic or asymptomatic, the best time to test post-exposure is less clear cut. Based on what I’ve read, 3–5 days after exposure is likely the best time to get tested, but a negative result isn’t a guarantee that you’re truly negative, so please continue to take precautions and consider getting yourself retested later in the 14-day incubation window.