Salmonella enteritidis, phage type 4 infection in a commercial layer flock in southern California: bacteriologic and epidemiologic findings

S. enteritidis, phage type 4 (SE PT4), was isolated from 5 of 6 layer chickens (27 weeks old) submitted for PM examination from a flock of 43 000. Bacteriological and epidemiological investigations on the ranch showed that 5 of the 8 flocks (176 000 birds) were infected. The prevalence of SE PT4 in randomly selected healthy birds ranged from 1.7% (in caged birds) to 50% (in free-range birds) and prevalence in culled birds (kept on dirt floor houses) ranged from 14% to 42%. The estimated overall prevalence of group D Salmonella in eggs contaminated with group D Salmonella was 2.28 per 10 000. The estimated prevalence of group D Salmonella in eggs from caged birds in 3 infected houses ranged from 1.5 to 4.1 per 10 000, whereas in 2 houses of free-range birds, prevalence was 14.9 to 19.1 per 10 000. Three of the 8 flocks on the ranch remained negative for Salmonella between May 1994 and December 1995 or until removed from the ranch. S. enteritidis PT4 was also isolated from 12.5% (6 of 48) of mice; 57% (4 of 7) of cats; and from 2 skunks tested. Environmental drag swabs and well water samples yielded multiple serotypes of Salmonella (23 of 180 and 5 of 14, respectively) but not S. enteritidis.