Over 2 million New Yorkers had coronavirus by March-end, 10 times more than official count: Study
An estimated 1 in 7 adults in New York had Covid-19 by the end of March, which is 10 times more than the official figure, according to a new study by the New York State Department of Health. This suggests that was significant undetected coronavirus transmission early in the outbreak. The first cases of Covid-19 were identified in New York State (NYS) in early March and since then NYS, particularly the metropolitan New York City (NYC) area, has become one of the most impacted communities in the US. As of May 9, over 335,000 laboratory-confirmed diagnoses have been made, accounting for approximately 25% of US diagnoses, says the research team, which also includes experts from the University at Albany School of Public Health. As of May 29, 368,284 confirmed cases have been reported from across the New York State.
“As with most infections, lab-confirmed diagnoses undercount the true population-level burden of infections. With SARS-CoV-2, the virus that causes Covid-19, key factors that contribute to underdiagnosis include absent or mild symptoms and access to testing. Thus although NYS has tested more residents for Covid-19 than any other state (over 1,180,000 persons tested through May 9, 2020), it is likely that laboratory-confirmed cases represent a relatively small portion of the total number of persons with a history of infection in NYS,” say researchers.
Accordingly, to provide a statewide picture of Covid-19 infection through late-March and diagnoses by early-April 2020, a cross-sectional seroprevalence study was conducted from April 19-28 by the New York State Department of Health. Antibody testing for SARS-CoV-2 has emerged as an important tool for understanding infection history. Serological tests measure the amount of antibodies or proteins present in the blood when the body is responding to a specific infection, such as Covid-19. In other words, the test detects the body’s immune response to the infection caused by the virus rather than detecting the virus itself.
The study covered 15,101 New Yorkers in 99 grocery stores across 26 counties, which contain 87.3% of the state’s population, located in all regions of New York State. Grocery stores were chosen as the testing venue because they were classified an essential business to remain open and, due to the necessity of grocery shopping, they attract a “heterogeneous clientele.” The researchers did finger pricks on shoppers (18 years and above) who volunteered to participate in the study. The blood tests showed that 1,887 of them had antibodies to the novel coronavirus, meaning they might have been infected in the past.
The findings estimate the extent of transmission of and community experience with SARS-CoV-2, particularly in the NYC metropolitan region. After statistical adjustment and extrapolation, the researchers estimated that over 2 million adults in New York State were infected through late March, with substantial variations by subpopulations. This is about 14% of all New York adults, or 1 out of 7, says the research team. The finding stands in sharp contrast to the case count at that time, which is about 189,000 cases, according to the study. “Following post-stratification weighting on region, sex, age, and race and ethnicity and adjustment for assay characteristics, estimated cumulative incidence through March 29 was 14.0%, corresponding to 2,139,300 infection-experienced adults,” says the pre-print published in medRxiv.
Cumulative incidence was higher among males (14.8%) than females (13.3%), with males comprising 50.3% of adult infections. This differed significantly by race and ethnicity. “Cumulative incidence was higher among Hispanic/Latino (29.2%), non-Hispanic black/African American (20.2%), and non-Hispanic Asian (12.4%) adults than nonHispanic white adults (8.1%). Cumulative incidence was highest in New York City at 22.7%,” it adds. Significant differences were also observed by age, ranging from the highest levels among persons 45-54 years old (16.0%) to the lowest among persons 55 years and above (12.1%).
Based on the analysis, the researchers say that monitoring, testing, and contact tracing remain essential public health strategies. “Despite large numbers of persons acquiring SARS-CoV-2, this represents only 14.0% of adult residents, suggesting that, even in this Covid-19 epicenter, the epidemic is substantially below the approximately 70% US herd immunity threshold. Against this remaining epidemic potential, ongoing vigilance through rigorous and extensive epidemic monitoring, testing, and contact tracing are necessary components for predicting, preventing, and/or mitigating a second epidemic wave, consistent with state and federal guidance for reopening,” say experts.