Online nonprobability survey estimates suggest that 54 million US COVID-19 infections went uncounted in official records after home tests were widely deployed and institutional testing waned starting in February 2022.
Before that time point, the percentage of adults reporting a positive COVID-19 at-home test was similar to results for institutional testing and wastewater monitoring, according to a study published yesterday in JAMA Network Open.
The findings, the Northeastern University-led research team says, suggest that such surveys can complement institutional and wastewater testing in an emerging pandemic and provide estimates of uncounted infections when rapid at-home tests are broadly available and institutional testing phases out.
To monitor COVID-19 case levels early in the pandemic, the United States implemented individual clinical testing, tracked hospital patients with COVID-19 symptoms, monitored patient SARS-CoV-2 antibody concentrations, and measured viral wastewater levels. Efforts focused on individual testing to evaluate local outbreaks, deploy resources, and begin or end public health mitigation measures.
"Throughout the pandemic, however, testing availability and reporting were inconsistent in the US," the researchers wrote.
"For example, the COVID-19 tests—designed by the US Centers for Disease Control and Prevention—were recalled due to a faulty reagent during the earlier months of 2020, heterogenous state policies regarding access to free institutional testing led to inconsistencies in interpreting case count data, and the massive government-led distribution of rapid at-home tests starting in January 2022 without a concurrent deployment of a centralized infection reporting system meant that there was low coverage of testing."
Survey, wastewater data may better capture cases
The researchers surveyed 306,799 adults in 50 US states and Washington, DC, 17 times from June 2020 through January 2023 on behalf of a multi-university consortium called the COVID States Project. The average respondent age was 42.8 years, and 66.0% were women.
The massive government-led distribution of rapid at-home tests starting in January 2022 without a concurrent deployment of a centralized infection reporting system meant that there was low coverage of testing.
The team compared survey-weighted estimates of monthly confirmed COVID-19 infections from January 2020 to January 2023 and uncounted test-confirmed cases from February 2022 to January 2023 with institutional COVID-19 infection data from Johns Hopkins University (JHU) and wastewater viral concentrations from Biobot Analytics.
In total, 15.9% of participants reported a positive COVID-19 test. From April 2020 to January 2022, before the government broadly deployed home tests, national survey-weighted confirmed COVID-19 case estimates were strongly correlated with institutional COVID-19 infection reports.
After January 2022, when at-home tests were widely available, the correlation was weak and no longer statistically significant, but survey COVID-19 case estimates correlated strongly with viral concentrations in wastewater before and after this time point.
COVID-19 infections reported by institutions correlated with viral wastewater levels before this time point but only weakly after, which the researchers said suggests that both survey and wastewater estimates may have better reflected test-confirmed COVID-19 infections thereafter. Similar correlation patterns were seen at the state level.
Role of survey data in emerging outbreaks
"Our survey estimates suggest that approximately 79 million (95% CI [confidence interval], 71 million to 86 million) confirmed cases may have occurred compared with 25 million reported in the JHU data," the authors wrote. "Based on national-level survey estimates, approximately 54 million COVID-19 cases were likely unaccounted for in official records between January 2022 and January 2023."
This study suggests that nonprobability survey data can be used to estimate the temporal evolution of test-confirmed infections during an emerging disease outbreak.
By state, the number of potentially uncounted infections ranged from 59,000 in Wyoming to 6.3 million in California.
"This study suggests that nonprobability survey data can be used to estimate the temporal evolution of test-confirmed infections during an emerging disease outbreak," the researchers concluded. "Self-reporting tools may enable government and health care officials to implement accessible and affordable at-home testing for efficient infection monitoring in the future."
