Salmonella enterica serovar London infections associated with consumption of infant formula

Epidemiologic studies were conducted on 31 cases of Salmonella group E infection detected in 2000 through a laboratory-based pathogen surveillance in Gangwon Province, Korea. Data were collected on the environmental exposures and the patients' foods, including the brand(s) of milk consumed before the onset of diarrhea. The patients' medical records were also reviewed. All of the patients were infants under 10 months of age except one 7-year old child. Surprisingly, all of the infants were fed with infant formulas from Company A, although two infants were fed with infant formulas from both Company A and Company B. Antimicrobial susceptibility test and pulsed-field gel electrophoresis (PFGE) were performed in 25 out of 31 isolates from the patients and in I isolate from an opened packet of infant formula collected from the home of an infected infant. All of the 26 isolates were Salmonella enterica serovar London. They showed a single PFGE pattern, and all of the isolates were susceptible to the 18 antibiotics tested. The causative agent of the salmonella outbreaks in the Gangwon Province and its surrounding areas was Salmonella London, and the highly likely source of the infection was infant formula from Company A.