COVID cases could be vastly undercounted because of home testing, experts say

The increasing popularity of home COVID-19 tests means that official reports of the number of people who have contracted the coronavirus during the current rise in cases may be a vast underestimate, experts say.

Official caseloads have been undercounts throughout the pandemic, because many people with COVID-19 don’t get tested, said Sean Clouston, an associate professor of public health at Stony Brook University. Home tests — results of which are not typically reported to health authorities — exacerbate the undercount, he said.

For example, even though the number of new cases in Suffolk County reported by the state Health Department for Thursday was 193, “there are probably more like 800 or 900,” Clouston said.

Although home tests mean fewer cases are counted, “by far the benefits of having home tests available outweigh any concerns or downsides of it being disruptive to the disease numbers,” said Dr. David Hirschwerk, an infectious disease expert and medical director of North Shore University Hospital in Manhasset.

“The most important thing is that people have easy access to testing and can get those tests done,” he said. People are more likely to get tested if it’s convenient, he said.

The state continues to count tests that are performed by doctors, pharmacists and other health professionals and are sent to laboratories for analysis.

“By understanding what the percent positivity is in all tests that are reported, we still will have an understanding of how much transmission is happening,” Hirschwerk said.

The percentage of coronavirus test results that come back positive has been steadily rising over the past few weeks as the highly contagious omicron subvariant BA.2 spreads.

Long Island’s seven-day positivity rate on Friday stood at 2.98%, nearly double the 1.52% rate on March 9 but still far lower than the rate of nearly 27% on a few days in early January. The one-day rate on Friday, 3.74%, was the highest since Feb. 8.

Clouston said it’s likely that the percentage of people who test positive with home tests is somewhat lower than the percentage who test positive in tests conducted by health professionals. Someone who goes out of their way to travel for a test may be more likely to have COVID-19 symptoms than someone who tests at home, he said.

Home tests were hard to find during the peak of the omicron surge in the early winter, but since then the federal government has been mailing free home tests to any household that requests them, and the state has ramped up its home-test distribution. Meanwhile, the state has been closing its COVID-19 test sites on Long Island and elsewhere in recent weeks.

How one county skewed the positivity rate

Home test results are not supposed to be included in the daily COVID-19 positivity rates and case numbers that the state Department of Health reports each day.

However, Onondaga County, which includes Syracuse, was reporting those results to the state, leading to a positivity rate in Central New York that was typically three or more times higher than the statewide rate. That also bumped up the statewide rate.

One of the problems is that the Onondaga County COVID-19 website asks residents to report positive results but not negative ones. The positivity rate is calculated by dividing the number of positive test results by the total number of results — meaning that the positivity rate was artificially inflated.

State Health Department spokeswoman Erin Silk said Saturday that Onondaga is believed to be the only county reporting home test results.

Future numbers won’t include the home tests, the governor's office said Friday. 

Clouston said a bigger concern than home tests affecting COVID-19 numbers is that, with less worry about the pandemic than in the past, many people won’t get tested at all.

Positivity rates reflect the extent of the spread from several days or a week ago, because of the time between infection and when people get tested, and the time it takes to process and report results, he said.

“When we’re on the uphill of a surge, it’s always much more dangerous than the numbers suggest,” he said.

State releases guidance on 2nd boosters

Meanwhile, on Saturday the state Health Department released guidance to the public and to health care providers on a second booster shot that mirrors Centers for Disease Control and Prevention guidance that was released Tuesday. The second boosters are now available at all state-run vaccination sites as well as places like pharmacies and doctors’ offices.

Immunity wanes over time after receiving vaccines, including initial boosters, and CDC data shows that those with booster shots are less likely to test positive for COVID-19 than those without boosters, and they’re less likely to get severely ill or die.

Anyone 50 and older who received a first booster shot at least four months ago is eligible for a second booster.

The state and CDC also are allowing a second booster for all adults who received a first booster of the Johnson & Johnson vaccine at least four months ago. In addition, anyone 12 and older who is severely or moderately immunocompromised is eligible for an additional shot. 

By David Olson

david.olson@newsday.com@DavidOlson11

David Olson covers health care. He has worked at Newsday since 2015 and previously covered immigration, multicultural issues and religion at The Press-Enterprise in Southern California.