CLUSTERS OF ACUTE APPENDICITIS - FURTHER EVIDENCE FOR AN INFECTIOUS ETIOLOGY

Background The aetiology of appendicitis, the commonest cause of acute abdomen, is unknown. Infection has been proposed but the evidence has been unconvincing. The purpose of the present study was to investigat e if temporo-spatial clustering and outbreaks, characteristics of infe ctious diseases, could be found in appendicitis cases in a defined Swe dish population. Methods. Temporo-spatial clustering among 1155 cases from three districts of Jonkoping County in 1984-1990 was identified b y Knox space-time cluster analysis. Outbreaks were identified by retro spective study of temporal variations in 3590 consecutive cases of acu te appendicitis from the city of Jonkoping in 1969-1990. Results. Spac e-time clustering was found among patients with operations less than 6 0 days apart (observed/expected [O/E]-ratio 1.46, P = 0.016). Subset a nalysis revealed clustering to be commonest among patients from the sa me households (O/E-ratio 6.52, P = 0.012), among patients younger than 15 years (O/E-ratio 3.61, P = 0.004) and among females (O/E-ratio 2.2 8, P = 0.004). Three outbreaks with a significantly increased number o f cases were observed during the 22-year study period (O/E-ratio 1.6-2 .2, P = 0.001-0.049). Conclusions. The finding of temporo-spatial inte raction and outbreaks among appendicitis cases supports the concept th at appendicitis may be caused by infectious agents.