Salmonellosis in infants: the importance of intrafamilial transmission.

In a retrospective review of Wisconsin Salmonella surveillance data, we found that 73 (39%) of 187 families with infant index patients has at least one family members with prior diarrheal illness, compared with only 20 (13%) of 158 families with 5- to 9-year-old index patients (P less than .0001). Prior diarrheal illness was also more commonly identified in families with an infant index patient 0 to 2 months of age (28 of 52 families) than in families with an index patient 3 to 11 months (45 of 135 families) (P less than .02); this difference was found largely in families of infant index patients with siblings. Intrafamilial transmission of Salmonella may explain a large proportion of cases of infant salmonellosis. Older children and adults with salmonellosis may be the most important exposures for infants 0 to 2 months of age.