Are Pandemic Hospitalization Numbers Misleading Us?

Researchers have tried to get at similar questions before. For two separate studies published in May, doctors in California read through several hundred charts of pediatric patients, one by one, to figure out why, exactly, each COVID-positive child had been admitted to the hospital. Did they need treatment for COVID, or was there some other reason for admission, like cancer treatment or a psychiatric episode, and the COVID diagnosis was merely incidental? According to the researchers, 40 to 45 percent of the hospitalizations that they examined were for patients in the latter group.

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The study found that from March 2020 through early January 2021—before vaccination was widespread, and before the Delta variant had arrived—the proportion of patients with mild or asymptomatic disease was 36 percent. From mid-January through the end of June 2021, however, that number rose to 48 percent. In other words, the study suggests that roughly half of all the hospitalized patients showing up on COVID-data dashboards in 2021 may have been admitted for another reason entirely, or had only a mild presentation of disease.

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But the study also demonstrates that hospitalization rates for COVID, as cited by journalists and policy makers, can be misleading, if not considered carefully. Clearly many patients right now are seriously ill. We also know that overcrowding of hospitals by COVID patients with even mild illness can have negative implications for patients in need of other care. At the same time, this study suggests that COVID hospitalization tallies can’t be taken as a simple measure of the prevalence of severe or even moderate disease, because they might inflate the true numbers by a factor of two. “As we look to shift from cases to hospitalizations as a metric to drive policy and assess level of risk to a community or state or country,” Doron told me, referring to decisions about school closures, business restrictions, mask requirements, and so on, “we should refine the definition of hospitalization. Those patients who are there with rather than from COVID don’t belong in the metric.”