Before pandemic started, pooled testing by RT-PCR revealed only two patients with SARS-COV-2 at Stanford: JAMA

SARS-COV-2 virions by EM: JAMA Open Network

A study of pooled samples, 292 in total, taken between January 1 to February 26, 2020, revealed only two positive results by RT-PCR (reverse transcriptase-polymerase chain reaction), both in late February.  This study, while intended to demonstrate the greater sensitivity of pooled samples from nasopharyngeal swabs and bronchoalveolar lavage (BAL), seems to have inadvertently demonstrated that the novel coronavirus wasn’t circulating undetected before the first positive patients came to light.

As a post yesterday noted, even the great sensitivity of RT-PCR is not able to detect all cases of the virus in the routine nasopharyngeal swab test– BAL is the most reliable way to detect the actual virus, showing it in 14 of 15 confirmed cases.  Nasopharyngeal swabs showed virus in roughly 75%, or three-quarters, of all confirmed cases.

The importance of these tests is that, first, swab testing will not detect the virus in all patients who have the infection.  BAL is most reliable, but it requires bronchoscopy, which is not a good idea because it can spread the virus all over the room during the procedure.  Second, the study referenced above shows that the virus was not present before it was first reported in late February in the San Francisco area.

Patients with typical symptoms of dry cough, fever, headache, and possibly sore throat, loss of sense of smell (without a stuffy nose) or upset stomach, vomiting, or diarrhea: assume that if there is novel coronavirus circulating in your community, you have it.  A SARS-COV-2 test may not be available due to shortages of supplies, and even if you have had the test, you may not get results for some days.  So isolate yourself, don’t go to work, and notify all your contacts that you are sick.  You don’t have to tell them that you have the novel coronavirus; you might have a cold or flu.  Regardless of your actual type of infection, you will prevent passing it on to others if you isolate yourself until you feel better.