Coronavirus antibody testing suggests infections are widely under-reported

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Mounting evidence suggests that the coronavirus might be more widespread throughout the country than previously thought -- in some cases more than 80 times original estimates -- as states expand capacity for antibody testing and find surprising results.

On Monday, New York Gov. Andrew Cuomo, who has emphasized the importance of antibody testing and contact tracing in order to determine who can safely return to work, said that early results suggested 14.9 percent of residents had contracted COVID-19 at some point.

When broken down by region, Cuomo said in New York City -- the state's hotbed for COVID-19 infections -- the rate was about 24.7 percent.

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He earlier said preliminary results suggested a statewide infection rate of 13.9 percent, which would mean roughly 2.7 million residents contracted the illness at some point, which is about 10 times more than what's been confirmed by COVID-19 testing. As of Tuesday, the number of coronavirus cases reported worldwide had reached just over 3 million.

The state had expanded antibody testing to 7,500 people, nearly double the total number tested five days earlier. As of Tuesday, 844,994 persons had been tested for COVID-19 statewide, resulting in 295,106 positive cases. New York, a state with over 8.9 million people, also has the highest number of coronavirus-related fatalities in the U.S., with at least 22,668.

But the state has largely reserved COVID-19 testing for symptomatic people, or those considered to be at-risk who had known exposure, before it began prioritizing antibody testing for health care and frontline workers, presenting a potential gap in the number reported versus the number of infections contracted.

NEARLY 3 MILLION NEW YORKERS HAVE HAD CORONAVIRUS, ANTIBODY STUDY SUGGESTS

An antibody test seeks to detect IgM and IgG antibodies against SARS-CoV-2, the virus that causes COVID-19, in serum, plasma or venipuncture whole blood from individuals who are suspected to have had it. IgG and IgM are antibodies that the body’s immune system produces in response to a virus, and are detectable as soon as several days after the initial infection. While officials have championed the test as a way to determine who is immune to the virus, others, including Dr. Anthony Fauci, have urged caution as it’s not yet clear what immunity means for this virus.

Still, the antibody results highlighted by Cuomo are the latest preliminary findings that suggest the true number of coronavirus cases is far greater than those reported by health department officials and the Centers for Disease Control and Prevention (CDC). Two other studies involving Santa Clara County in California and another in LA County have suggested the same.

In Santa Clara County, Stanford University-led researchers found the number of cases may actually be up to 85 times higher than what health officials have tallied, while LA County results suggested the number of infected persons there may be between 28 to 55 times higher than currently confirmed COVID-19 cases.

“We haven’t known the true extent of COVID-19 infections in our community because we have only tested people with symptoms, and the availability of tests has been limited,” said Neeraj Sood, lead investigator of the LA County study and professor of public policy at the USC Price School for Public Policy. “The estimates also suggest that we might have to recalibrate disease prediction models and rethink public health strategies.”

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In addition to the risk that “silent carriers," or asymptomatic patients, can pose to others, the new data may also help researchers better estimate the virus’ true fatality rate.

“Many estimates of fatality rate use a ratio of deaths to lagged cases (because of duration from case confirmation to death), with an infections-to-cases ratio in the 1-5 fold range as an estimate of under-ascertainment,” wrote the Stanford University researchers. “Our study suggests that adjustments for under-ascertainment may need to be much higher.”

Fox News' Greg Norman contributed to this report.