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Salmonellosis from Inadequately Pasteurized Milk -- Kentucky

In late April 1984, three isolates of Salmonella typhimurium, all from specimens from persons associated with a convent in western Kentucky, were reported by the Kentucky Division for Laboratory Services to the Division of Epidemiology. Subsequent investigation revealed that at least 16 cases of gastroenteritis (predominantly diarrhea) were associated with the convent between March 28 and May 2. The likely vehicle was inadequately pasteurized milk.

One hundred forty nuns reside at the convent; additional persons are employed as caretakers, foodhandlers, and farm workers. All meals are prepared in the convent kitchen and are available to residents and employees.

In early May, 180 (90%) of 200 persons at risk filled out questionnaires on basic demographic information, recent gastrointestinal illness, and frequency of consuming milk, raw milk, chicken, turkey, pork, and eggs. Sixteen (9%) persons met the case definition of a positive stool culture for S. typhimurium or at least three loose stools per day lasting 2 or more days or any three of the following symptoms: fever, diarrhea (not meeting the criteria above), nausea and/or vomiting, or abdominal cramps; 12 additional persons (7%) who had gastrointestinal symptoms but did not meet the case definition were excluded from the statistical analysis. Ill persons had diarrhea (100%), abdominal cramps (63%), nausea (50%), fever (44%), and vomiting (13%). Diarrhea lasted 1-8 days (median 3 days), with two to 11 loose stools per day (median five). Patients were 21 years to 86 years of age (median 67 years). Fifteen (94%) were female, and 14 (88%) were convent residents. Three (19%) of the 16 consulted a physician.

Of persons filling out questionnaires, 14 (15%) of 91 persons who admitted drinking pasteurized milk became ill, but only two (3%) of 75 who claimed not to have drunk milk became ill. Persons drinking pasteurized milk were approximately six times more likely to develop illness (p = 0.01). No other risk factors were identified.

Fourteen (88%) of the 16 ill persons had onset on or after March 28, with three clusters of cases approximately 2 weeks apart. In late April, 24 symptomatic nuns and 18 asymptomatic foodhandlers submitted single stool-culture specimens. Five (31%) of the 16 ill persons, all nuns, had stool cultures positive for S. typhimurium; eight (50%) were negative; and three (19%) had no stool specimen submitted. A 69-year-old culture-positive ill nun was hospitalized for a Guillain-Barre-like illness 20 days after onset of gastrointestinal symptoms. A raw milk sample collected May 9 also yielded S. typhimurium. The isolate from milk and three isolates from humans had identical plasmid profiles. The remaining two human isolates were reported to be identical to each other and were probably equivalent to the other isolates. Antibiograms of all six isolates were the same.

Before early March 1984, the convent had its own herd of dairy cattle and pasteurized its own milk. At that time, the convent began purchasing raw milk from a Grade-A dairy farm in the area. Since the fall of 1983, this latter dairy herd reportedly has had a recurrent problem with gastroenteritis, although no fecal sampling has been performed.

The purchased milk was pasteurized at the convent in 50-gallon lots in a 60-gallon steam pasteurizer. No time-temperature gauge/record or air space heater was available. Pasteurization temperatures and holding times during the epidemic period are not known but may have been as low as 54.5 C (130 F) for only 30 minutes.

A milk sample collected May 4, reportedly pasteurized to 62.8 C (145 F) for 30 minutes, was weakly phosphatase-positive, indicating inadequate pasteurization. A butter sample collected the same day was strongly phosphatase-positive.

Based on the identical plasmid profiles of S. typhimurium isolated from milk and humans, the evidence of inadequate pasteurization, and the association between milk consumption and illness, it was concluded that inadequate milk pasteurization accounted for this outbreak. Preventive recommendations centered around the pasteurization process: use of a recording thermometer and air space heater, pasteurization at 65.6 C (150 F) for 35-40 minutes, and routine phosphatase and bacteriologic testing.

No further cases have been reported. Reported by D Adams, S Well, MA, Green River District Health Dept, BF Brown, MD, S Gregorio, DrPH, Div of Laboratory Svcs, L Townsend, Milk Control Br, JW Skaggs, DVM, Div of Epidemiology, MW Hinds, MD, State Epidemiologist, Kentucky Dept of Health Svcs; Div of Field Svcs, Epidemiology Program Office, Enteric Diseases Br, Div of Bacterial Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Salmonellosis caused by S. typhimurium transmitted in raw milk has been previously identified in Kentucky (1). The outbreak described here differs from the earlier one in that inadequate milk pasteurization, rather than raw milk consumption, accounted for the outbreak. Unpasteurized milk is a common cause of outbreaks and sporadic cases of disease in the United States. The list of bacteria responsible for illnesses caused by consumption of raw and inadequately pasteurized milk includes various Salmonella species, Campylobacter, Brucella, Escherichia coli, Yersinia enterocolitica, and Listeria (2). Recently, a large outbreak of illness occurring in older age groups characterized by profuse diarrhea lasting more than 4 weeks has been under investigation in Minnesota (3); the causative agent is not yet known, but there is a clear epidemiologic association with drinking raw milk. Health professionals and persons responsible for milk regulations should be aware of the many health hazards associated with drinking unpasteurized or inadequately pasteurized milk.


  1. CDC. Salmonellosis--Kentucky. MMWR 1977;26:239.

  2. Potter ME, Kaufman AF, Blake PA, Feldman RA. Unpasteurized milk--the hazards of a health fetish. JAMA (in press).

  3. Minnesota Department of Health. Chronic diarrhea in Brainerd, Minnesota. Disease Control Newsletter 1984;11:57-8.

Addendum: Volume 33, No.36, page 506 The following persons should be added to the credits: J Simon, MPH, T Waters, PhD, Health Svcs, Tennessee Valley Authority, Chattanooga, Tennessee.

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