Meteorological Factors Influence on Hospitalization for Respiratory Diseases And Symptoms in the South Israel

Introduction:
For world public health, research on climate change and its influence on health becomes very important. A significant part of such research concerns with the effects of meteorological factors on various health outcomes. The objective of our study was to evaluate the role of meteorological factors, typical for semi-desert areas, in daily number of emergency hospital admissions due to diseases of respiratory system (ICD-9 ## 460–519) and symptoms, signs and ill-defined conditions of various systems (ICD-9 ## 780–790).
Methods:
As health outcome, we used daily hospital records obtained from a medical center in the south Israel. During the study period (a whole 1999 year), 4002 and 13292 hospital admissions for respiratory diseases and symptoms were observed correspondingly. As meteorological variables, discomfort index, maximum daily temperature and relative humidity were used. To estimate running and delayed meteorologically connected health effects, the Poisson regression model with special time series technique to control seasonality was fitted to the dataset. Indirect impact of the meteorological factors was evaluated by pairs of trigonometric functions with different cycles. The final model included meteorological parameters and variables represented by the pairs of trigonometric functions with the cycles of a year, a half of year, a 3-months-period, a 4-months-period. These particular cycles were chosen after results of harmonic analysis.
Results:
Running direct effects of humidity and discomfort index were observed for number of emergency hospitalization for the given symptoms and diseases correspondingly. Delayed direct association was found between: 1) temperature, discomfort index and hospitalization for the symptoms (one, 2 days lagged); 2) humidity and hospitalization for the symptoms (3-days-lag); 3) humidity and hospitalization for respiratory diseases (1, 2 days lagged). Indirect running and one-day-lagged effects of all three meteorological factors in both groups of hospitalization causes were observed. More delayed indirect association was similar, but without: temperature effect on hospitalization for respiratory diseases (2-days-lag); temperature and discomfort index effects on hospitalization for the symptoms (3-days-lag).
Discussion and Conclusions:
Despite the relatively short study period and necessity of further confirmation, these findings suggest significant direct and indirect effects of maximum daily temperature and humidity, and discomfort index on hospital admissions for the considered symptoms and respiratory diseases. The results of one-year observations do not describe the annual variations, but they were enough to determine a significant influence of seasonal tendency on controlled outcomes. Analysis of the obtained results shows that they are biologically sound.