A: Not necessarily. You should consider the possibility that you got a negative test result even though you are truly infected.
After you are exposed to SARS-CoV-2, the amount of virus in your body builds up over time, reaching 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, which is known as the incubation period. Based on this incubation period and because it is ideal to identify cases before they even develop symptoms, public health experts currently recommend people get tested about 4 days after a suspected exposure.
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 (i.e., they get a false negative result). As outlined in the article below, the false negative rate (i.e., proportion of those who are truly positive that get a negative test result) 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.
Of note, these estimates are based off of tests primarily performed among symptomatic individuals, so less is known about the false negative rate among individuals who are asymptomatic (i.e., will never develop symptoms) and pre-symptomatic (i.e., will develop symptoms, but haven’t yet), who may still transmit infection to others. While the Food and Drug Administration just released recommendations for labs and manufacturers that want to perform tests in people who don’t have symptoms, they warn that, if a test is intended for screening an asymptomatic population, “Negative results must be considered in the context of an individual’s recent exposures, history, presence of clinical signs and symptoms consistent with COVID-19.”
Overall, if you have reason to think you were recently exposed and you get a negative PCR test result, you should consider the possibility that the result may be a false negative, continue to monitor for symptoms and minimize contact with others. If you don’t have a suspected recent exposure, you can be more confident that a negative test result means you truly aren’t infected. The safest thing for anyone who wants to visit relatives that are high risk for complications from COVID-19, however, is to self-quarantine for 14 days beforehand, whether or not you suspect you were recently exposed, and then visit them outdoors, while maintaining 6 ft distance and wearing a mask.