Outbreaks of food-borne disease--a common occurrence but rarely reported.

To the Editor: Salmonella infections are among the most prevalent recognised communicable diseases caused by bacteria, and a major cause of food poisoning throughout the world. The Enteric Diseases Reference Unit (EDRU) of the National Institute for Communicable Diseases (NICD) is a reference centre in South Africa (SA) for various enteric pathogens including Salmonella, and participates in national laboratory-based surveillance for Salmonella. Isolates are voluntarily submitted to the EDRU from ~120 clinical microbiology laboratories covering all provinces across the country. We report an outbreak of food-borne disease among schoolteachers at Rob Ferreira High School in White River, Mpumalanga, in December 2006, which occurred after eating food prepared by the school kitchen. The causative agent was identified as S. enterica serotype Virchow (Salmonella Virchow). Twenty-two bacterial isolates were obtained for analysis following culture from patients’ rectal swabs. All isolates were susceptible to ampicillin, augmentin, trimethoprim, sulfamethoxazole, chloramphenicol, streptomycin, tetracycline, kanamycin, imipenem, nalidixic acid, ciprofloxacin, ceftriaxone and ceftazidime. Pulsed-field gel electrophoresis (PFGE) analysis of XbaI digested genomic DNA of bacteria revealed an identical pattern for all 22 outbreak strains which, together with identical antimicrobial susceptibility profiles for all isolates, determined that the outbreak was caused by a single strain of bacterium.