Background: The present study investigated the monthly variation of acute appendicitis and its association with climatic factors (ambient temperature, relative humidity, atmospheric pressure, rainfall, and hours of sunshine) using a nationwide population-based data set in Taiwan. Methods: We identified 237,760 first-time hospitalizations for acute appendicitis from 2000 to 2009. We used the auto-regressive integrated moving average method to examine the monthly variation in the acute appendicitis incidence rates after adjusting for the time-trend effect and seasonality. Results: Throughout the 10-year study period, we found that the monthly incidence rate of acute appendicitis demonstrated a fairly similar monthly pattern for each gender independently and for the pooled data. May through July had the greatest rates, decreasing in August to a trough in February. We used the autoregressive integrated moving average test for seasonality and found a significant difference in the monthly incidence rate for the pooled genders and for the male- and female-only groups (all P <0.001). Furthermore, the auto-regressive integrated moving average regression models for the male, female, and combined groups all suggested that a significant positive association exists between the monthly incidence rates of acute appendicitis per 100,000 population and the ambient temperature after adjusting for time trends and month. Conclusions: The results of our study have revealed a significant difference in the monthly incidence rate of acute appendicitis.
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