The health risks of breathing polluted air spike when the flu season does, according to a major new study spanning six US metropolitan areas.
New research has found that the link between air pollution and emergency hospital visits for breathing problems becomes stronger during flu season, with the two appearing to amplify each other’s effects, rather than simply adding to the burden.
The team, led by researchers at Emory University, analysed more than 6.6 million respiratory emergency visits across six US cities over 12 flu seasons. They paired daily pollution measurements with weekly, laboratory-confirmed influenza hospitalisation rates from CDC surveillance data.
It was seen that when flu activity was high, the risk of breathing-related hospital visits from PM2.5 exposure was also higher than during low-flu periods.
For nitrogen dioxide (NO2), the trend was even clearer: as flu levels increased, so did the risk of respiratory and COPD problems – steadily and consistently.
In Atlanta, for example, a rise in PM2.5 during peak flu weeks was linked to a 3.5% increase in respiratory ED visits, compared to no significant effect during low-influenza periods. San Francisco showed a similar pattern.
The authors write: ‘This study demonstrates that influenza activity may modify the pollution-health associations in a non-linear pattern with geographical heterogeneity. The health effects of air pollution cannot be fully understood in isolation from concurrent infectious disease dynamics.’
The researchers caution that the relationship is not simply additive. In some cities, the strongest pollution effects were seen at moderate rather than peak influenza levels—a pattern that may reflect a ‘saturation effect,’ where the most vulnerable individuals have already been affected by the virus, leaving a smaller pool susceptible to pollution.
The pattern wasn’t the same everywhere. In Salt Lake City, flu season made NO₂ more harmful, bumping up respiratory and pneumonia risks by 2 – 4%. But in Albany, the link between pollution and hospital visits actually got weaker as flu increased – proof that local conditions shape the risk.
Biologically, it makes sense. Pollution inflames the lungs and weakens immune defences. Flu damages the protective barrier in the airways. Together, they can overwhelm the body.
The study suggests that even modest reductions in air pollution during flu season could yield disproportionate benefits, and that integrated strategies combining air quality management with influenza prevention – such as vaccination campaigns timed to coincide with pollution forecasts – could reduce the compounded burden on healthcare systems.
the authors conclude.: ‘These findings underscore the need for integrated air quality and infectious disease surveillance to mitigate seasonal respiratory health burdens.’
The full research can be read here.
Photo: SHVETS production
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