Prolonged incubation period of salmonellosis in an outbreak of Salmonella enteritidis infection.

An outbreak of Salmonella enteritidis infections occurred in Otaru, Japan, in September 1997. A total of 143 cases of salmonellosis were reported to the local Public Health Center. In this outbreak, one case had a 214-hr incubation period. We investigated 5 isolates including this case by phage typing and pulsed-field gel electrophoresis (PFGE) to determine the genetic heterogeneity of S. enteritidis. Five isolates were phage typed as reacted, but did not conform (RDNC) with identical reaction patterns and had quite similar PFGE patterns. Thus, the prolonged incubation period may not be attributed to genetic heterogeneity of the organism but rather to other factors.