What to know about coronavirus testing

As of April 20, 134,612 of Nassau and Suffolk’s 2.8 million people have been tested for COVID-19, with 59,901 testing positive.

As of April 19, 167,330 people per day are being tested, for a total of 3,865,864, according to the COVID Tracking Project.

A growing consensus of health professionals and public officials say vastly increasing testing is key to understanding the spread and profile of the virus and getting it under control. Estimates of the figures of tests needed per day range from 500,000 to hundreds of millions, though one conservative-leaning group says bumping up tests to a couple million per week may suffice.

As it now stands, we have only a limited profile of the disease based almost exclusively on people who are displaying systems. Most testing sites won’t even test those with weaker symptoms of the virus, much less those with no symptoms at all.

A large portion of COVID-19-infected people, as high as 80 percent, show no signs at all. Worse, nasal swab testing machines have been known to produce false negatives of up to 30 percent. Those two phenomena could potentially send infected people out into society.

They can carry and spread the disease just as quickly as infected people who show symptoms. That’s why public officials and health experts want to vastly increase testing before society is opened up. That includes randomized testing and testing ostensibly healthy people to catch those stealth carriers.

The diagnostic test takes a sample from the nasal cavity and throat of a person, combines mucous from the swab with chemicals called reagents and runs it through a device called an RT-PCR machine to check for genetic material of the virus. The immunology test uses a small sample of a subject’s blood to look for the presence of specific antibodies associated with COVID-19, an indication that he or she has internally battled the disease and, presumably, built up an immunity to it. Nearly all of the currently available tests are diagnostic.

Cuomo on Sunday announced plans to test the blood of 3,000 people across the state, beginning Monday, to determine the percent of the population that recovered from the virus. The test, known as a “serosurvey,” draws on participants from supermarkets around the state, including one in Nassau County. The World Health Organization and the National Institutes of Health are rolling out “serosurveys” on the global and national levels as well.

Testing that focuses just on the visibly sick vastly undercounts the full impact of the pandemic, and can skew reported infection rates to provide a false picture of its spread. The current positive rate for COVID-19 across the U.S. is about 20% of those tested. But in countries like South Korea and Germany, which have done considerably more testing per capita, the figure is 3% to 7% respectively. Experts say that a test-positive rate above 10 percent likely reflects “inadequate testing.”

There has not yet been definitive proof that people with COVID-19 antibodies are immune from reinfection, and if they are for how long. Dr. Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, on Friday acknowledged that the extent and length of protection provided by antibodies has yet to be established definitively, but that previous viruses provide some guidance. “We are assuming that if you’re infected and you have antibodies, you’re protected,” he said.