Estimating COVID-19 case prevalence in New York City

By Tarun Sai LomteMay 2 2022Reviewed by Aimee Molineux

In a recent study posted to the medRxiv* preprint server, researchers estimated the prevalence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in New York City (NYC).

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources

Background

Routine surveillance of coronavirus disease 2019 (COVID-19) cases might not represent the true prevalence of SARS-CoV-2 among the general population due to untested or undiagnosed cases and the lack of home-based tests results (reflecting) in the case surveillance in the United States (US). The underestimation of cases could vary by sociodemographic and geographic factors.

Concerns regarding the disparities in interpreting COVID-19 case counts, test positivity rates, and case rates caused the US Centers for Disease Control and Prevention (CDC) to revise the guidelines for community metrics of COVID-19, emphasizing hospital admissions and deaths. An increase in hospitalizations and fatalities resulting from a surge in COVID-19 cases lags behind the surges in community transmission, therefore missing early mitigation opportunities.

The study and findings

In the present study, researchers estimated the prevalence of SARS-CoV-2 between January 1, 2022, and March 16, 2022, when the SARS-CoV-2 Omicron BA.1 variant was predominant.

A cross-sectional survey of adults in NYC was conducted from March 14 – 16, 2022, and the respondents were inquired about COVID-19 testing and results from January 1, 2022. The questionnaire captured information on viral tests such as polymerase chain reaction (PCR), antigen tests, and home-based rapid tests. Respondents were asked about all types of COVID-19-symptoms experienced during the study period and confirmed or probable COVID-19 cases among close contacts.

Symptoms included fever, nasal congestion or runny nose, cough, dyspnea, fatigue, sore throat, body or headaches, loss of taste/smell, nausea, and diarrhea. Survey weights were developed to account for differences in group distribution that included educational attainment, self-identified sex, race or ethnicity, and region. The inference population was 6.6 million adult New Yorkers.  

The authors classified the study population into confirmed, probable, and possible cases. A confirmed case was defined as one who self-reported one/or more positive test results with a testing or healthcare provider. A probable case reported a positive test result based on an exclusive at-home rapid test (not followed-up with a confirmatory diagnostic test).

A possible case was an individual who never took a test or tested negative during the study period and self-reported COVID-19-related symptoms with a known epidemiologic link, i.e., close contact with one or more confirmed or probable case(s). The researchers estimated the proportion of participants using these three mutually exclusive case classifications. The differences between testers and non-differences were computed using Pearson’s chi-squared test of independence.

Overall, 1030 individuals were surveyed, of which 46.1% were non-testers. The research team estimated that 27.4% of adult New Yorkers, corresponding to 1.8 million of about 6.6 million adults, might have been infected by SARS-CoV-2 during the study period. Of these, 14.1% were confirmed cases, 5.2% were probable cases, and 8.1% were possible cases. About 41.3% test positivity rate was estimated for those who tested with a healthcare or testing provider.

A high COVID-19 prevalence was noted for all age groups with substantial variation based on geography and sociodemographic factors. The estimated prevalence was higher among those recognized as highly vulnerable to severe COVID-19 outcomes, including non-vaccinated adults. Testing individuals were likely Hispanic, aged 18 – 34 years, with higher education and (household) income levels (> $65,000) than non-testers.

Conclusions

The authors observed a high COVID-19 prevalence among adult NYC residents during the second half of the Omicron surge in the city, with an estimated proportion being 1.8 million adults. The characteristics of people testing with providers differed significantly from non-testers, indicating the challenges of relying solely on the surveillance data of testing for gaining insights into epidemiology and the burden of community transmission.

Interestingly, during the study period, the case surveillance data from the NYC Department of Health and Mental Hygiene reported that around 6.7% (552,084) of the entire NYC population tested with a testing or healthcare provider by PCR or rapid antigen tests. The seven-day moving average of the test positivity rate varied during the study period from 34.8% on January 1 to 1.6% on March 16, with an overall 11.8% positivity.

Compared with the estimated proportion, the findings highlight the extent of the underestimated case burden during the surge. This latent case prevalence could be plausibly explained by non-testing, exclusive home-based tests, or testing too soon after exposure or onset of symptoms.

A few limitations include the recall bias in measuring test outcomes and symptoms given the self-reporting over a long recall period. Moreover, adolescents and children were excluded from the study, and the small sample size could limit the precision of some estimates.

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources