An Outbreak of Shigellosis due to Shigella _exneri Serotype 3a in a Prison in Iran

Background: On June 16 and 17, 2007, the medical clinic of a prison in Isfahan, Iran received multiple reports of gastrointestinal illness among prisoners. A cross-sectional study was therefore undertaken to determine the extent, causative agent and possible source of the outbreak. Methods: A case-patient was de_ned and patient information was collected with a standardized questionnaire. Stool samples were collected from the patients and restaurant employees, and analyzed for the presence of enteric bacteria by routine bacteriological methods. Shigella isolates were identi_ed and serotyped by commercially available antisera. The relationship between the strains was determined using antimicrobial drug resistance pattern analysis and enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR). Results: Seven hundred one inmates experienced gastrointestinal illness and severe diarrhea. The attack rate was 14.02%. Rectal swabs and stool cultures recovered from patients tested positive for Shigella _exneri serotype 3a. All tested isolates had a similar antibiotic resistance and ERIC-PCR pattern. Our _ndings demonstrated that raw vegetables were more likely to be the causative agent of this outbreak. Conclusion: The results indicated that a single clone of S. _exneri was responsible for this outbreak. Although we could not trace the exact origin of the organism, the consumption of raw vegetables one day prior to the onset of illness was strongly associated with an increased risk of S. _exneri infection. This study emphasizes the need for accurate monitoring and surveillance of food and vegetables consumed in prisons.