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Flu Hits America’s Poor Hardest, Study Finds

February 25, 2016

People who live in poorer American neighborhoods face a number of health disparities, and a new study led by the Yale School of Public Health indicates that increased rates of hospitalization from influenza is yet another issue facing the less affluent.

In a report published in the Centers for Disease Control and Prevention’s (CDC) Morbidity and Mortality Weekly Report, researchers led by James Hadler, M.D., M.P.H., clinical professor of epidemiology at the Yale School of Public Health, reveals that residents of neighborhoods with high numbers of people living below the poverty line are twice as likely to be hospitalized for influenza than their peers residing in wealthier areas. This holds true across all age, racial and ethnic groups, Hadler said.

Because data on socioeconomic measures are generally not included in public health surveillance data, Hadler’s team had to find a novel way to determine the role of poverty on influenza infection.

“We have data by age, by sex, by race and by ethnicity, but we didn’t have data on socioeconomic status for any of the problems that we were working on,” Hadler said. Surveillance data does, however, include residential addresses, which form part of the standard set of information collected with lab results, the main initial surveillance source for information that leads to determining influenza hospitalization rates. The team used that information to geocode their data, and merged it with information from U.S. Census tracts that provided information on poverty rates in those areas.

Hadler and his team conducted the study through the Connecticut site of the CDC’s Emerging Infections Program (EIP), based in part at the School of Public Health. The EIP is a CDC-led consortium of sites across 10 states, through which data is collected on a number of infectious diseases. Connecticut’s program is a collaboration between the Connecticut Department of Public Health and Yale, funded by a cooperative agreement from the CDC. Yale has been an EIP collaborative site since 1995, when the program began.

This kind of analysis is an important step forward in better understanding and building effective responses to the disparities in public health delivery that plague the U.S. health care system.

Robert Heimer

The Connecticut EIP team had previously found an association between census tract poverty and influenza-related hospitalization in New Haven County. It then encouraged the other nine EIP sites to geocode their data. Using data from across all 10 EIP sites plus four others included in CDC’s FluSurv-NET, they analyzed data which encompassed more than 27 million people, and found that the disparity in Connecticut was, in fact, a national result.

Yale’s EIP Director Robert Heimer, Ph.D., professor at the School of Public Health, noted that applying neighborhood level socioeconomic data, rather than individual data, to influenza surveillance has never been done before. “This kind of analysis is an important step forward in better understanding and building effective responses to the disparities in public health delivery that plague the U.S. health care system,” he said.

Hadler, who served as the Connecticut State Epidemiologist for 25 years before coming to Yale, suggests three contributing factors to the team’s findings: low rates of influenza vaccination in underserved communities; high rates of household crowding, which increases the amount of close personal contact which helps spread respiratory illness; and high rates of underlying medical conditions, such as asthma, in those living below the poverty line. Whenever a person’s underlying medical conditions are not well controlled, which often happens with limited access to care, influenza can tip the balance and result in a need for hospitalization, said Hadler.

Based on the team’s findings, Hadler recommends an effort by public health authorities and clinicians to make a stronger push to ensure people in underserved areas get the flu vaccine each year. In addition, he recommends a more aggressive use of antiviral agents, which are effective in countering the effects of influenza, as a way to avoid hospitalizations.

Submitted by Denise Meyer on February 25, 2016