As the number of COVID-19 cases on Long Island continues to rise, New York is obtaining fewer test results because of newly relaxed reporting rules and the increased use of home-test kits.
As of last week, testing facilities no longer must notify the state when someone tests negative on a rapid test. That, and the lack of reporting of home-test results, make the closely watched coronavirus positivity rate — the percent of tests that come back positive — less complete.
But experts and state officials said that won’t affect the ability to monitor and control the spread of the virus.
“I don’t think that it will make a huge difference in terms of tracking this pandemic moving forward, because the positives will still count in the case rates,” said Wafaa Al-Sadr, a professor of epidemiology and medicine at the Columbia University Mailman School of Public Health.
WHAT TO KNOW
- The state last week stopped mandating that laboratories and testing sites such as schools and nursing homes report negative results from COVID-19 antigen — also called rapid — tests.
- That move, along with the increasing use of home COVID-19 tests, results of which typically are not reported to health authorities, means the state is getting less coronavirus testing data.
- But the state and experts say there is still enough information from PCR tests, positive rapid test results and hospitalizations to adequately track the spread of the coronavirus.
The case rate is the number of COVID-19 cases per 100,000 people, which is unaffected by the change, because testing facilities still must report all positive results from rapid tests, also known as antigen tests, said Eli Rosenberg, deputy director for science for the state Health Department’s Office of Public Health.
“Our assessment of cases is no less complete,” he said.
Long Island's seven-day average of cases per 100,000 people has surged from 6.38 on March 9 to 26.33 on Tuesday, state Department of Health statistics show. In the week ending Tuesday, there were 5,233 newly reported cases, more than four times the 1,268 confirmed cases in the week ending March 9.
A change in calculating positivity rates
The positivity rate is the percent of tests analyzed by laboratories and testing sites that come back positive divided by the number of total tests. Until April 4, for example, a 4% positivity rate meant 4% of all tests reported to the state were positive.
The state stopped counting negative antigen results April 4, so it no longer uses any antigen tests to calculate its positivity rates, because counting only positive but not negative results would lead to an inflated percentage of positive tests, Rosenberg said.
Only about a quarter of test results had been from antigen tests, he said. The rest are PCR tests.
Even with the change, “We’re still going to be able to get a sense” of the trajectory of the pandemic by comparing positivity rates from today with those from a few weeks or months ago, said Dr. David Hirschwerk, medical director of North Shore University Hospital in Manhasset and an infectious disease expert.
Long Island's seven-day average of positivity rates has more than tripled in the past month, from 1.52% on March 9 to 4.95% on Tuesday.
Positivity rates for antigen and PCR tests reported to the state are similar, Rosenberg said. The day the state stopped including antigen tests in the positivity rate, the rate rose modestly, following the trend from the previous several days.
“We found it made a very negligible difference whether you include the antigens in that metric or not, which is why with this change in the HHS rule that we adopted, we felt very comfortable that we could compute the positivity only among the PCRs,” Rosenberg said.
He was referring to how the U.S. Department of Health and Human Services, beginning April 4, stopped requiring testing facilities to report negative antigen results. State and local health departments could continue mandating the reporting of negative results, HHS said in a March 8 memo. But a state Health Department spokesman said the state typically follows federal guidance.
HHS officials did not respond to questions on why the agency made the change.
Rosenberg said that, unlike PCR test analysis, which is typically automated, “Many antigen tests involve a manual reading,” and the mandate that every negative antigen test be reported was “a huge burden” on testing facilities such as nursing homes and schools.
He said the case per 100,000 measurement is a better way to track the spread of the coronavirus.
“What you really want to know is what amount of the population has recently gotten COVID, what fraction of the population is newly diagnosed with COVID,” he said. “That’s what the rates are telling you.”
Home testing contributes to undercount
Although case rates are “an important metric,” they are an undercount, because an increasing number of people test at home and never report results, El-Sadr said.
“The case rates as we move forward are going to be less and less reliable because of the shifting to a lot of people doing home testing,” she said.
Rosenberg said it’s unclear what percent of tests are done at home, but the state is “looking into that.”
El-Sadr said case numbers always have been an undercount, because many people who contracted the coronavirus were never tested for it.
Looking at COVID-19 hospitalization levels is more reliable because “that’s not influenced by whether you test at home or tested somewhere else,” El-Sadr said.
But that is a “lagging indicator,” because people aren’t hospitalized for COVID-19 until days after they contract the virus, so hospitalizations don’t measure the current spread of the virus, Hirschwerk said.