Background and purpose: Some previous research links stroke incidence to weather, some links strokes to air pollution, and some report seasonal effects. Alveolar inflammation was proposed as the mechanistic link. We present a unified model of time, weather, pollution, and upper respiratory infection (URI) incidence.
Methods: We combined existing databases: US Environmental Protection Agency pollution levels, National Weather Service data, counts of airborne allergens, and New York City Health and Hospitals Corporation counts of stroke, asthma, and URI patients. We used autoregressive integrated moving average modeling (a statistical time series modeling technique) with stroke admissions as the response variable and day of week, holidays, September 11th, and other counts and levels as explanatory variables.
Results: Using a broad definition of stroke, there were 5.1+/-2.3 stroke admissions per day: narrowly defined, 4.2+/-2.1 strokes per day. There are relatively fewer strokes on Sundays (0.50 strokes; P=0.0011), Saturdays (0.62; P<0.0001), Fridays (0.38; P=0.0009) and holidays (0.875; P=0.0016). We found relatively small, independent exacerbating effects of higher air temperature (P=0.0211), dry air (P=0.0187), URIs, (P<0.0001), grass pollen (P=0.0341), sulfur dioxide (SO2; P=0.0471), and suspended particles <10 microm in size (P=0.0404). These effects are modest: < or =0.6, 0.6, 2.4, 1, 0.9, and 0.7 strokes per day, respectively. We did not find statistically significant exacerbating effects of other variables.
Conclusions: We found statistically significant, independent exacerbating effects of warmer, drier air, URIs, grass pollen, SO2, and particulate air pollution. The model supports the theory that links pulmonary inflammation to stroke.