The incidence of acute ischemic cerebral events in relation to environmental factors, pollution, and time

Study objectives: We relate the incidence of acute ischemic cerebral events (AICE) to environmental factors, pollution, and time. Methods: This was a population-based study in which we identified all patients with AICE (a transient ischemic attack or an acute ischemic stroke) using discharge International Classification of Diseases, Ninth Revision codes from 27 hospitals in the Buffalo metropolitan area of Erie County, NY, during 1 year from January 1, 2000, to December 31, 2000. Study investigators confirmed the diagnosis by individually reviewing medical records. We obtained temperature and precipitation data from the National Weather Service. Pollution data were obtained from the Environmental Protection Agency. Data were analyzed with χ2 tests and linear regression using SAS software (version 9). Results: We analyzed 2,462 patients with AICE during the study period. The highest, lowest, and median temperatures were 26°C, -16°C, and 10°C, respectively. Bivariate analysis shows a small, statistically significant increase in AICE on weekdays compared with weekend days (P=.0016) and a significant increase in AICE as temperature increases (P=.0033). Multivariate linear regression shows about 1 fewer event per day on weekends (P=.0029) and a reduction of 0.4 events per day with each decrease in temperature of 10°C (P=.0037). We found no statistically significant relationship between the incidence of AICE and precipitation, nitrogen dioxide, all oxides of nitrogen, sulfur dioxide, ozone, and particles less than 0.4 μm. Conclusion: There is a significant increase in the number of AICE patients admitted on weekdays compared with weekends in the study area. As temperature increases, the incidence of AICE increases significantly in the study population.