False Positive

Local Test Ruled False Positive by State Health Department —

Miller Report for the Week of June 1, 2020

By William Miller, MD – Chief of Staff at MCDH

Reviewing all of the facts of a situation is important before jumping to conclusions. Last week, one of our staff who works at North Coast Family Health Center had a positive test result for COVID-19. The test was done elsewhere as part of routine pre-procedure screening. The person never had any symptoms and their last date of working in the clinic was 7 days previously. Also, the person had no patient contacts in the preceding 14 days. Given a number of aspects of the case, we suspected that this might be a false positive. We immediately conferred with the County Health Department, consulting with both Drs. Doohan and Flaherty, our County Health Officer and Deputy Health Officer respectively. When the person returned to Ft. Bragg where they live, they were immediately retested using two different brands of analyzers and both were negative. “It was the two negatives on same day [as the first test], run on two different machines, that made me think it was false positive,” stated Dr. Doohan.  We then presented the findings to the California Department of Public Health who had their adjudication team review the case and they officially declared it a false positive.  

A false positive means that the test turned positive when the infection is not actually present.  It is an error.  All medical tests have the potential for errors and false results.  There are many reasons that a test could give such an erroneous result.  With PCR tests, one potential problem can be cross contamination since PCR can detect extremely small amounts of the genetic material of the virus.  Thus, even a small accidental contamination in the lab or at the testing site could turn the test positive when it should have been negative.  It could also be a problem with the chemical reaction of the test itself that for some reason did not react the way it was supposed to.  Another possible source of lab error is mislabeling of the sample with the wrong patient’s name.  All of these errors can and do occur.

The implications for this being a false positive are important for us here on the Mendocino Coast.  It means that we still have no evidence of community spread.  This will help us justify carefully rolling back on some more of the shelter-in-place stipulations.   We should keep in mind that will also mean opening our community back up to tourism and other influx from the outside.  People who live here will also begin to travel elsewhere to visit friends and relatives or go on vacations.  While opening back up to tourism is crucial for our economic survival, it will invariably also bring with it the coronavirus.  It is unavoidable and there will certainly come a day, probably not in the too distant future when we will have the virus here.  At that point, a strong community surveillance-testing program and contact tracing will be imperative.

The County Health Department is working with Mendocino Coast District Hospital, Mendocino Coast Clinics and the City of Ft. Bragg, to set up such a testing program.  Despite claims at the federal level that “anyone who wants to get a test can”, it remains a challenge for many rural communities like ours to have such readily available testing that would allow ongoing surveillance of the population.

So, one might say, why did we go through all of this shelter-in-place stuff if we are eventually going to have it here in our community anyway?  The answer is, that by doing this, we have avoided overloading our health care system.  If our health care system had become overloaded and crashed, then a lot more people would die and not just from COVID.  So, while the price we have paid is high, the benefit is real.  The key to keeping that benefit, which we have paid for so dearly, is maintaining social distancing, wearing face coverings and washing our hands.  As simple as these three things might sound, they will absolutely have a really big effect on controlling further transmission.

Leave a Reply

Your email address will not be published.