Prevalence of respiratory infections likely under-reported

Currently, the prevalence (or “burden”) of respiratory viral infections is limited by the ways in which data are collected. This is because infections are typically only counted by healthcare institutions when individuals seek healthcare. In other words, if someone has a respiratory illness but does not go to the doctor, they are not included in the total count of infections. Therefore, the current methods of collecting data do not capture those who are infected but asymptomatic or those who choose not to seek care. Furthermore, current metrics used to assess individuals when they do seek care complicate these numbers.

In order to determine what percentage of the community is typically infected, the researchers conducted a 2 year-study in New York City in which over 200 participants were tested weekly for multiple respiratory viral infections and asked to record daily symptoms. The authors then analyzed this data alongside a sample of patients seeking care at three NYC pediatric hospitals and city-wide laboratory results reported to the Department of Health & Mental Hygiene. How does the actual prevalence of respiratory illnesses match up with those recorded through doctors’ visits?

Overall, the authors found that the commonly used metric of influenza-like illnesses (ILI), typically defined as a fever, sore throat and/or cough, is an insufficient way of understanding the general prevalence of respiratory infections. To begin with, most of the ILI events reported by participants were not medically attended to. Expanding this further, the authors assert that relying on reported ILI events to estimate respiratory viral infections would miss 95% of infections. This is due to both asymptomatic cases as well as positive cases with symptoms where people did not seek medical attention. In addition, relying only on ILI misses respiratory illnesses that do not meet ILI’s metrics of fever, sore throat, and/or cough. Overall, the general finding was that current surveillance methods, based on healthcare data, disproportionately captured viruses with more severe symptoms, missing many other viral infections (including infections with the 4 endemic coronaviruses) in the general population.

The authors’ findings have particular implications for public health directives, especially with regard to asymptomatic cases of respiratory illnesses. They note that measures such as vaccines and isolation are only as effective as the total prevalence of the virus is known, which includes asymptomatic cases. This has recently become a reality as the world fights back against the COVID-19 pandemic. Finally, the authors suggest that active longitudinal sampling for respiratory virus infections could be an important addition to the current methods of health-care based surveillance for respiratory illnesses.

Reference:
Galanti M, Comito D, Ligon C, Lane B, Matienzo N, Abrahim S, Shittu A, Tagne E, Birger R, Ud-Dean M, Filip I, Morita H, Rabadan R, Anthony S, Freyer GA, Dayan P, Shopsin B, Shaman J. Active surveillance documents rates of clinical care seeking due to respiratory illness. Influenza Other Respi Viruses. 2020;00:1–8. https://doi.org/10.1111/irv.12753