Association of normal weather periods and El Nino events with hospitalization for viral pneumonia in females: California, 1983-1998

Objectives. This study examined associations between weather and hospitaliz ations of females for viral pneumonia during normal weather periods and El Nino events in the California counties of Sacramento and Yolo, San Francisc o and San Mateo, and Los Angeles and Orange. Methods. Associations between weather and hospitalizations (lagged 7 days) for January 1983 through June 1998 were evaluated with Poisson regression m odels. Generalized estimating equations were used to adjust for autocorrela tion and overdispersion. Data were summed over 4 days. Results. Associations varied by region. Hospitalizations in San Francisco a nd Los Angeles increased significantly (30%-50%) with a 5 degreesF decrease in minimum temperature. Hospitalizations in Sacramento increased significa ntly (25%-40%) with a 5 degreesF decrease in maximum temperature difference . The associations were independent of season. El Nino events were associat ed with hospitalizations only in Sacramento, with significant decreases for girls and increases for women. Conclusions. The results suggest that viral pneumonia could continue to be a major public health issue, with a significant association between weather and hospitalizations, even as the global mean temperature continues to ris e. An understanding of population sensitivity under different weather condi tions could lead to an improved understanding of virus transmission.