Nursery salmonellosis: delayed recognition due to unusually long incubation period.

A nursery outbreak of diarrheal illness caused by Salmonella nienstedten initially involved seven infants cared for in one nursery; secondary infection subsequently affected one infant cared for in the same nursery as well as four other infants. Recognition of the outbreak was delayed due to an unusually long incubation period. The period from last known exposure to onset of diarrhea ranged from two to 18 days, with a median of ten days. The prolonged incubation period may have resulted from a low inoculum of the organism, from a previously unknown characteristic of Salmonella nienstedten, or may be an age-specific response. Hospital infection control personnel should be aware that nosocomial cases of salmonellosis may have a longer incubation period than has been previously recognized.