Thread by @DearPandemic

1/ Q: I want to visit older family members soon, so I went and got a #PCR test for #COVID__19 (i.e., the kind that detects *current* infection). My test came back negative, so I am in the clear, right?
A: Not necessarily. It is possible you got a false negative test result.

2/ After you are exposed to #SARSCoV2, the amount of #virus in your body builds up over time. It reaches its highest level right before symptom onset.
It can take 2-14 days (average of 5-6) from the time of exposure to when symptoms develop: a.k.a. the incubation period.

3/ Based on this incubation period, and because it is ideal to identify cases before they even develop symptoms, #publichealth experts currently recommend people get tested about 4 days AFTER a suspected exposure.

4/ It is possible, however, that someone could be infected, but not yet have built up enough virus to generate a positive result at the time they are tested.
This results in a #falsenegative.

5/ As outlined in this @TheAtlantic article: theatlantic.com/science/archiv…
the false negative rate of PCR tests was estimated in one model to be 100% on the day you are exposed, 40% on day 4 after exposure and 20% on day 8 after exposure.

6/ Overall, if you have reason to think you were recently exposed, consider that a negative result MAY be a false negative.
Keep #selfmonitoring symptoms. And remember: the safest thing to do is self-quarantine for 14 days before visiting relatives at high risk of complications.