In the early stages of the COVID-19 pandemic, as is generally the case with the emergence of a novel virus like SARS-CoV-2, data on testing, detection, and case reporting, which are necessary for estimating the true burden of a disease were lacking or not available. More specifically, in some heavily affected areas of the United States, the size of the COVID-19 outbreak quickly exceeded the capacity of health systems to complete detailed reporting on cases that included information like the age of the patient and whether or not they were hospitalized. This led to case reports sent to CDC that were missing vital patient information. CDC had to estimate the age and hospitalization status of patients with missing data based on cases with known information on age and hospitalization status. To inform how to make estimates of disease burden for COVID-19, we relied on our experiences estimating influenza disease burden. CDC has been monitoring testing practices for influenza (flu) among hospitalized patients since 2010 to make estimates of annual disease burden of flu in the United States. Nearly a decade of flu data collection and analysis has shown respiratory disease testing varies in different parts of the country, by care settings, for different age groups, and at differing levels of disease severity. The data available so far on COVID-19 testing practices are limited across these variables. Once more complete data across these variables are available, COVID-19 burden estimates will be updated.
As additional data become available on the sensitivity of the SARS-CoV-2 tests, these data will also help refine COVID-19 infection, illness, and hospitalization estimates.