The most commonly used diagnostic test for COVID-19, called the PCR test, provides a simple yes-no answer to the question of whether a patient is infected. But a yes-no result is not very useful. It is amount of viruses that will dictate the next steps for a patient infected with COVID-19.
The PCR test amplifies genetic material from the virus in cycles; the fewer cycles required, the greater the amount of virus or virus load in the sample. The greater the viral load, the more likely the patient is to be contagious. This cycle threshold is never included in the results sent to physicians and coronavirus patients, although it may tell them how contagious the patients actually are.
Apoorva Mandavilli for The New York Times:
Researchers say the solution is not to test less, or to skip testing people without symptoms, as recently suggested by the Centers for Disease Control and Prevention. Instead, new data underscores the need for more widespread use of rapid tests, although they are less sensitive.
“The decision not to test asymptomatic people is just very recurring,” said Dr. Michael Mina, an epidemiologist at the Harvard TH Chan School of Public Health, referring to the CDC recommendation. “We should actually try to test all different people,” he said, “but we have to do it through completely different mechanisms.”
In what may be a step in that direction, the Trump administration announced Thursday [August 27] that it would buy 150 million quick tests …
“We’ve used one type of data for everything, and that’s just pluses – that’s all,” said Dr. Mina. “We use it for clinical diagnostics, for public health, for decision-making processes … It is really irresponsible, I think, to relinquish the recognition that this is a quantitative question.”
In three sets of test data including cycle thresholds, compiled by officials in Massachusetts, New York and Nevada, up to 90 percent of the positive tests had barely any virus, a review of The times found. On Thursday, the United States registered 45,604 new cases of coronavirus, according to a database maintained by The times. If the infection rates in Massachusetts and New York were to apply nationwide, perhaps only 4,500 of these people might actually need to isolate themselves and submit to contact tracking …
Most tests set the limit at 40, a few at 37. This means that you are positive for coronavirus if the test process required up to 40 cycles, or 37, to detect the virus. Any test with a cycle threshold above 35 is too sensitive, agreed Juliet Morrison, a virologist at the University of California, Riverside. “I’m shocked that people would think that 40 could represent a positive,” she said. A more affordable cut would be 30 to 35, she added. Dr. Mina said he would set the number to 30, or even less.
Officials at the Wadsworth Center, New York State Laboratory, have access to CT scores from tests they have performed, and analyzed their numbers on The times‘ request. In July, the laboratory identified 794 positive tests, based on a 40-cycle threshold. With a cutoff of 35, about half of these tests would no longer qualify as positive. About 70 percent would no longer be judged positive if the cycles were limited to 30.
In Massachusetts, 85 to 90 percent of those who tested positive in July with a cycle threshold of 40 would have been considered negative if the threshold was 30 cycles, Dr. Mina said. “I would say that none of these people should be tracked, not one,” he said.
MacDailyNews Take: Making decisions with bad data has long had an abbreviation known by computer programmers: GIGO (garbage in, garbage out).
Making political decisions – including closing schools, companies, stores, etc. – with poor COVID test data is a recipe for garbage decisions.
We have even caused Apple to close its stores, at least in part based on COVID-19 cases. GIGO.
It is important that this situation can be remedied. The report notes that the FDA says that people can have a low virus load when they are newly infected, so a test with less sensitivity will miss these infections. But that problem is easily solved, as Dr. Mina said The times“Test them again, six hours later or 15 hours later or whatever,” he said. A quick test would find these patients quickly, although it was less sensitive, because their viral load would increase rapidly.
What is needed is a COVID test that is fast, inexpensive and plentiful enough to test often anyone who needs it – even if the test is less sensitive. “It may not capture every single one of the sending humans, but it will certainly capture the most transferable humans, including super-spreaders,” said Dr. Mina The times. “Only that would drive epidemics to virtually zero.”