Hi Mark,

I read one of your posts in response to someone asking if a DNA pcr assay at 13 days post exposure could be considered accurate. You said no. However, if one is infected aren't there millions of virus floating around the body and infecting cells right off the bat? If that's the case, how could a supersensitive pcr assay test fail to not find it? You said they are good at picking infections up when they're present, but not good at ruling out infection. I don't understand the logic. Thanks for your time!!!

We will probably never have the data to answer the question of when in a population of acutely infected people is the first day that PCR tests are positive. That would require infecting people and then getting daily blood tests to answer that question. You are correct though, in the right clinical setting of high risk exposure, if the test is positive, it is highly likely that infection is present. The likelihood of false positives is very small. However, if the test is negative at 13-14 days, that does not necessarily rule out infection because it may be too early. Thus the test is a false negative in someone truly infected, but the test is negative. Alternatively it is a true negative in someone not infected. Therefore if it's positive, it's useful information, if it's negative, and I suspect infection, I would retest some weeks later.

MH