Increases in the relative rates of culture negative pneumonia (1%-2%) requiring hospitalization and emergency department (ED) visits were significantly associated with increased concentrations of fine particulate air pollution (PM2.5) in the previous 2 to 7 days, according to a study published in the Annals of the American Thoracic Society. In addition, increased relative rates of influenza requiring ED visits (3%-4%) but not hospitalization were associated with increased PM2.5 concentrations in the previous 5 to 7 days.

In a case-crossover study, investigators utilized records of respiratory infection hospital admissions and ED visits retained by Statewide Planning and Research Cooperative System (SPARCS) for all adult New York State residents (≥18 years of age) who lived within 15 miles of 6 urban air-monitoring stations (Buffalo, Rochester, Albany, the Bronx, Manhattan, and Queens) where hourly PM2.5 concentrations are monitored. Data included rates of healthcare encounters in the previous 1 to 7 days for total of 498,188 residents with primary diagnoses of influenza, bacterial pneumonia, or culture negative pneumonia from January 1, 2005 to December 31, 2016. The differences between the time periods before (2005 to 2007), during (2008 to 2013), and after (2014 to 2016) were evaluated with respect to air quality policies and economic changes.

The majority of patients had healthcare encounters for culture negative pneumonia (89%, 77%, and 68%, respectively) in the before, during, and after periods. Interquartile range (IQR) increases in PM2.5 in the previous 2 to 7 days in patients with culture negative pneumonia were associated with increased hospitalization rates, the biggest increases  in the previous 5 days (excess rate [ER], 2.5%; 95% CI, 1.8%-3.2%) and 6 days (ER, 2.5%; 95% CI, 1.7%-3.2%). There were no associations between PM2.5 and influenza hospitalizations, but there were IQR increases in the previous 5 to 7 days that were associated with increased rates of ED visits in patients with influenza, with the biggest increase  at 7 days (ER, 3.9%; 95% CI, 2.1%-5.6%). Furthermore, increased rates for influenza ED visits and culture negative pneumonia hospitalizations were associated with each 6.4 µg/m3 and 6.2 µg/m3 increases, respectively, in PM2.5 concentrations in the previous 3 days.

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Several limitations exist for this study. Regardless of how close they lived to a PM2.5 monitoring site, all study participants were assigned the same PM2.5 concentrations, potentially leading to exposure misclassification and resulting in a bias toward the null hypothesis.

The researchers concluded that “increased rates of culture negative pneumonia healthcare encounters, ED visits for influenza, and hospitalizations for bacterial pneumonia were associated with increased concentrations of PM2.5 over the previous few days,” and that the “relationship between different types of respiratory infections and changing compositions of air pollution mixtures during and after periods of improved air quality requires further study.”

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Croft DP, Zhang W, Lin S, et al. The association between respiratory infection and air pollution in the setting of air quality policy and economic change [published online November 6, 2018]. Ann Am Thorac Soc. doi:10.1513/annalsats.201810-691oc