Patients hospitalized for influenza had increased odds of heart attack and stroke in the following weeks and months, according to a new study led by Temple College of Public Health epidemiologist and assistant professor Erin Kulick. Kulick and collaborators from Columbia University established the connection after analyzing the large New York Statewide Planning and Research Cooperative System (SPARCS) database, which includes about 98 percent of all hospitalizations in the state. 

“In looking at trigger factors for stroke and heart attack, there’s been promising research indicating it could be due to an inflammatory response, or brought on by some sort of infection,” Kulick said.

The new study, published in the journal BMC Public Health, examines 33,742 hospital patients in the database identified as having suffered an ischemic stroke—the type when blood flow to the brain is restricted—and 53,094 who had myocardial infarction (MI), or heart attack, in 2014. Those patient records were checked for any hospitalizations for influenza-like illness (ILI) during the year prior to the cardiovascular event, in various time windows from 15 to 365 days prior. Equivalent time windows were examined for each patient for the previous two years, to function as control data and allow comparison of odds.

ILI events in the 15 days prior were associated with a 39% increase in odds of ischemic stroke. Hospitalization for ILI over the prior 365 days was associated with an almost 70% increase in odds of stroke. The findings for heart attack were a little different: the effect of ILI hospitalization on MI was strongest in the 15 days prior, increasing the odds of having a MI by 24%.  These findings indicate possible differences in mechanism behind the risk of stroke compared to the risk of MI after ILI, Kulick said. 

The study also looked at whether these relations differed across a series of demographic factors.  Among individuals living in rural areas, the risk of ischemic stroke following ILI was higher in the first 90-day as compared to individuals living in urban areas. The association between ILI and myocardial infarction varied across race, with whites having significantly higher ILI-associated MI across all time periods. 

In separate research, Kulick said, the researchers also have found that the seasonality of cardiovascular events, specifically stroke and MI, is associated with flu seasons, with higher rates of stroke and MI seen in years with higher numbers of flu cases.

While further research is needed to understand elevated risks of cardiovascular events after influenza, the study does offer some guidance for doctors.

“Clinicians should be aware when they have higher risk patients with influenza that the risk of having a stroke or heart attack is significantly higher,” Kulick said.