Adults who had underlying medical conditions and then developed the [flu](https://www.mcknights.com/news/flu-hospitalization-rates-highest-older-adults-cdc-reports/) were four times more likely to be hospitalized with the virus compared to those who didn’t have underlying medical issues, according to data from the US Centers for Disease Control and Prevention (CDC).
The CDC [study](https://academic.oup.com/jid/advance-article-abstract/doi/10.1093/infdis/jiaf164/8099211), which was published March 28 in _The Journal of Infectious Diseases,_ relied on electric health record and billing data to calculate flu-related hospitalization rates and pair it with data on underlying medical conditions. Data was derived from 870,888 participants, 1,403 of whom were hospitalized with the flu at least once within a season across the four seasons studied.
The median age of participants was 46 years old, and 44% had received a flu vaccine. In total, 42% of participants had at least one underlying medical condition. Participants were adults at two healthcare systems in California and Minnesota over the course of four respiratory virus seasons, from 2016 to 2020.
Underlying medical conditions studied included asthma, blood disorders, cerebrovascular disease, diabetes, chronic obstructive pulmonary disease (COPD), ischemic heart disease, liver disease, neurologic or musculoskeletal disorders, chronic kidney disease, rheumatologic or autoimmune conditions, and congestive heart failure.
Compared to those without heart failure, the rate of flu-related hospitalization was highest for patients with congestive heart failure followed by COPD and blood disorders, the data showed. The rate went up the more underlying medical conditions that a person had compared to those with no underlying medical conditions, the researchers noted.
“Among those with varying types and number of UMCs, if vaccination prevalence had been lower than observed, influenza-associated hospitalization rates would have been higher,” the study authors wrote. “These findings highlight the importance of preventive medical care and annual influenza vaccination in reducing influenza-associated hospitalizations, particularly for individuals at high-risk.”