Surveillance for dust storms and respiratory diseases in Washington State, 1991

Southeast Washington State, which has a long history of seasonal dust storms, experienced 2 d of dust storms in October 1991, during which PM10 levels exceeded 1,000 micrograms/m3 (i.e., six times greater than the Environmental Protection Agency's 24-h PM10 standard). Three community hospitals in southeast Washington were visited for the purpose of assessing the possible effects of dust storms on respiratory health. During these visits, the number of emergency room visits for respiratory disorders for each day of 1991 were abstracted. These numbers were compared with daily PM10 levels for 1991. Also determined were the observed/expected ratios for the number of emergency room visits for each respiratory disorder category during October 1991. The maximum observed/expected ratio for the respiratory disorders was 1.2. For 1991, we found a 3.5% increase in the number of daily emergency room visits for bronchitis for each 100 micrograms/m3 increase in PM10. In addition, 2 d subsequent to those days on which the PM10 levels exceeded 150 micrograms/m3, there was a 4.5% increase in the number of emergency room visits for sinusitis for each 100 micrograms/m3 increase in PM10. Our results indicate that the naturally occurring PM10 in this setting has a small effect on the respiratory health of the population in general.