WASHINGTON : Testing people for COVID-19 too early in the course of infection may result in a false negative diagnosis, even though they may eventually test positive for the virus, according to a study which says it is best performed three days after the symptoms appear.The review research, published in the journal Annals of Internal Medicine, assessed data on RT-PCR tests -- which detect viral genetic material in samples -- from seven prior studies.In the analysis, the researchers from Johns Hopkins University in the US analysed a total of 1,330 respiratory swab samples from a variety of subjects including hospitalised patients."A negative test, whether or not a person has symptoms, doesn't guarantee that they aren't infected by the.