摘要：Objectives. This study examined associations between weather and hospitalizations of females for viral pneumonia during normal weather periods and El Niño events in the California counties of Sacramento and Yolo, San Francisco 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 models. Generalized estimating equations were used to adjust for autocorrelation and overdispersion. Data were summed over 4 days. Results. Associations varied by region. Hospitalizations in San Francisco and Los Angeles increased significantly (30%–50%) with a 5°F decrease in minimum temperature. Hospitalizations in Sacramento increased significantly (25%–40%) with a 5°F decrease in maximum temperature difference. The associations were independent of season. El Niño events were associated 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 rise. An understanding of population sensitivity under different weather conditions could lead to an improved understanding of virus transmission. Recent assessments of the potential health effects of climate variability and change concluded that the distribution and incidence of any disease associated with weather may change with a changing climate. 1 , 2 Climate variability and change may increase or decrease the distribution and incidence of weather-sensitive diseases. To estimate the potential size of this effect, we must start with an understanding of the existing associations between specific health outcomes and various weather variables. However, there are large gaps in our knowledge of the specific weather variables associated with weather-sensitive diseases, with the possible exceptions of heat waves and certain infectious diseases. For example, the fact that colds and influenza have seasonal patterns has long been known, but the reasons have not. It is projected that by 2100, global mean surface air temperatures will increase by 1°C to 3.5°C relative to 1900. 3 The average rate of warming under the various scenarios considered by the Intergovernmental Panel on Climate Change will probably be greater than any seen in the last 10 000 years. The actual annual to decadal weather patterns will likely include considerable natural variability. Regional temperature changes could differ substantially from the global mean values. During the 1900s, the contiguous United States warmed by approximately 1°F and precipitation increased, with much of the increase due to increases in heavy precipitation events ( >5 cm/day) and decreases in light precipitation events. 4 , 5 There is considerable interest, but a great deal of uncertainty, regarding whether increasing global mean temperatures will be associated with changes in the occurrence and intensity of El Niño Southern Oscillation events. 6 , 7 The El Niño Southern Oscillation is a climate phenomenon that describes the periodic changes in oceanic and atmospheric circulation patterns in the tropical Pacific Ocean. El Niño and La Niña events are the 2 extremes of the El Niño Southern Oscillation. El Niño events, which are associated with a warming of the tropical Pacific sea surface temperature, occur approximately every 2 to 7 years. El Niño events can have a strong effect on local weather patterns. For example, in southern and central California, El Niño winters tend to get more rain than usual. During the years 1983 through 1998, there were 5 El Niño events (1982–1983, 1986–1987, 1991–1993, 1994–1995, and 1997–1998). Although there is uncertainty as to whether the frequency and magnitude of El Niño events might change with increasing global mean temperatures, studying what happened during recent El Niño events provides information on the sensitivity of diseases to specific changes in weather patterns. El Niño events are “natural experiments” with worldwide impacts. Until recently, almost no research looked at how the distribution and rate of health outcomes varied, if at all, during El Niño events. 8 Understanding these relationships is useful for developing current public health responses, for evaluating population vulnerability to these events, and for designing future adaptation measures. This project was designed to describe and compare the existing associations between certain weather variables and hospitalizations for viral pneumonia during normal weather periods and El Niño events. Changing weather variables do not cause pneumonia, but they may set up conditions that facilitate increased or decreased viral transmission.
