Epidemic Salmonella enteritidis infection in Los Angeles County, California. The predominance of phage type 4

Abstract

Between April and July 1994, 501 cases of Salmonella enteritidis infection were reported in Los Angeles County, California, nearly 5 times the number reported between April and July 1993; of these, 422 (84%) were sporadic (not related to known outbreaks). A case-control study was done to determine risk factors for sporadic illness; the distribution of S enteritidis phage types was evaluated. Case-patients (n = 58) were county residents older than 1 year with culture-confirmed S enteritidis infection in August 1994. One to two acquaintance controls (n = 98) were matched to each case by age, sex, and race. Two risk factors-eating raw or undercooked eggs (matched odds ratio [MOR] = 6.6; 95% confidence interval [CI] = 1.9, 23.0) and eating in restaurants (MOR = 4.9; 95% CI = 1.2, 19.4) in the 3 days before the onset of illness-remained significant in the conditional logistic regression model. Of 16 randomly selected S enteritidis case-isolates, 15 (94%) were phage type 4. The reasons for the regional predominance of phage type 4, an S enteritidis subtype recently associated with large and destructive increases in salmonellosis among poultry and humans in Britain and much of Europe, are unclear. To minimize human S enteritidis infection, food service workers need frequent training in the proper handling of raw foods, eggs should be kept refrigerated during distribution and storage, and eggs should be cooked until the yolk is firm, particularly for persons at the greatest risk for serious illness: pregnant women, elderly persons, and those with compromised immune systems. Clinicians should obtain stool specimens for culture from patients who present with diarrhea and fever or bloody diarrhea or who are possibly part of an outbreak.