Seasonal variation in onset of acute appendicitis

Purpose. Several acute diseases exhibit a circannual pattern. The present study was aimed to verify the possible existence of a seasonal variability in the onset of acute appendicitis (AA). Patients and Methods. All cases of AA diagnosed at the St Anna Hospital of Ferrara, Italy, from 1998 to 2004, were considered. The total sample was divided into subgroups by gender, age (≤19 and ≥20 years), and ICD9-CM code. For statistical analysis, the distribution of symptom onset was tested for uniformity by the χ2 test for goodness of fit, and chronobiological analysis was performed by applying partial Fourier series. Results. In the 7-year period analysis, 1331 consecutive cases of AA (673 males) were observed. The analysis showed, for total population, a seasonal variation with a peak in summer and a nadir in spring. Subjects ≤19 years (n=654) showed a higher frequency of events in winter (winter=191 cases, 29.2%; spring=154 cases, 23.5%, summer=142 cases, 21.7%, autumn=167 cases, 25.5%, χ2=8.07 p=0,046), whereas subjects ≥20 years (n=677) showed a higher frequency in summer (winter=150, 22.2%, spring=151, 22.3%, summer=214, 31.6%, autumn=162, 23.9%, χ2=16.33 p=0,001; difference between the two groups: χ2: 19.2, p<0.001). Cases of AA with peritonitis (ICD-9 540.0, n=90), were more frequent in summer (winter=18, 20%, spring=19, 21.17%, summer=38, 42.2%, autumn=15, 16.7%, χ2=14.22, p=0.002), and chronobiological analysis found a statistically significant peak of higher incidence in July (PR 68.2, 95%CL: May-September, p=0.006). Conclusions. The existence of a seasonal pattern in the onset of AA is confirmed, with differences in relation to age.