I got tired of writing about the problem of false positive tests for the coronavirus, so I gave up. Now the New York Times has suddenly become aware of the problem. When a PCR test is run the virus is amplified in proportion to the number of cycles run. Typically 40 cycles are performed. Thus, high a number of cycles may detect viral fragments which are not associated with an infection, or at least one of sufficient magnitude to be contagious.
Your Coronavirus Test Is Positive. Maybe It Shouldn’t Be is the title of an article in the NY Times updated Sept 15. It quotes Dr. Michael Mina, an epidemiologist at the Harvard T.H. Chan School of Public Health. He says, “In Massachusetts, from 85 to 90 percent of people who tested positive in July with a cycle threshold of 40 would have been deemed negative if the threshold were 30 cycles.”
“The number of people with positive results who aren’t infectious is particularly concerning,” said Scott Becker, executive director of the Association of Public Health Laboratories. “That worries me a lot, just because it’s so high,” he said, adding that the organization intended to meet with Dr. Mina to discuss the issue.
Read the article for a complete discussion. But a large number of false positive tests combined with a declining death rate has caused one wag to declaim that an epidemic has been replaced by a “casedemic”. We are not going to test our way out of COVID-19. It will eventually go away, or we’ll make it vanish with a safe and effective vaccine.
The graphs below show cases and deaths for the US versus time. As you can see cases have risen while deaths have fallen.
