Correspondence
An Outbreak of Salmonella Infection from Ice Cream
N Engl J Med 1996; 335:824-825September 12, 1996
- Article
To the Editor:
In their study of a national outbreak of Salmonella enteritidis infections associated with the consumption of ice cream (May 16 issue),1 Hennessy and colleagues show how effective the appropriate use of epidemiologic tools can be. However, I question their nationwide estimates of infection. The data presented strongly suggest that cases were significantly more common in a specific area (southeastern Minnesota) than in other areas, findings possibly associated with a specific date of ice cream manufacture (August 26, 1994). The high concentration of cases in this area is not explained by increased testing alone.
It seems more likely that the tanker trailers used to transport the ice cream premix were not uniformly contaminated (it is unclear how many were used for the ice cream involved in the outbreak) and that only a few trucks (especially one or more related to the August 26 lot) had a substantial degree of contamination. If this was the case, the results should not be extrapolated to provide the national incidence. The cross-sectional study does not help answer whether the higher attack rates in southeastern Minnesota were specifically associated with the consumption of ice cream from the August 26 lot. Although I agree with the possibility that cases were underreported, it still seems highly probable that the total number of cases was significantly lower than that proposed by the authors.
1 ReferencesMiguel O'Ryan, M.D.
University of Chile, Santiago, Chile1
Hennessy TW ,Hedberg CW ,Slutsker L , et al. A national outbreak of Salmonella enteritidis infections from ice cream. N Engl J Med 1996;334:1281-1286
Full Text | Web of Science | Medline
To the Editor:
In England and Wales two outbreaks of S. enteritidis phage type 4 infection associated with the consumption of ice cream were reported to the Communicable Disease Surveillance Centre of the Public Health Laboratory Service between 1990 and 1995. Twenty-five people were affected in an outbreak in 1992, and S. enteritidis phage type 4 was isolated from the stools of 9 of 14 who were tested. A cohort study indicated that commercially produced ice cream was the source of infection, and there was evidence that it had been contaminated by contact with other food. The ice cream was stored “semi-frozen” in a refrigerator with an unacceptable cooling temperature. The second outbreak affected seven members of a hotel staff, and stool specimens from four of them were positive for S. enteritidis phage type 4. Statistical evidence indicated that the vehicle of infection was ice cream made on the premises with raw eggs.
S. enteritidis phage type 4 has been a major public health problem in England and Wales, and it has largely been associated with the consumption of contaminated raw hens' eggs.1-3 The microbiologic quality of commercially produced ice cream manufactured in the United Kingdom is generally good,4 and the occasional outbreaks of food poisoning caused by ice cream have been due to cross-contamination or to homemade ice cream containing unpasteurized hens' eggs.
4 ReferencesTamara Djuretic, M.D.
Patrick G. Wall, M.D.
Gordon Nichols, Ph.D.
Public Health Laboratory Service, London NW9 5DF, United Kingdom1
Irwin DJ ,Rao M ,Barham DW , et al. An outbreak of infection with Salmonella enteritidis phage type 4 associated with the use of raw shell eggs. Commun Dis Rep CDR Rev 1993;3:R179-R183
Medline2
Humphrey TJ ,Baskerville A ,Mawer S ,Rowe B ,Hopper S . Salmonella enteritidis phage type 4 from the contents of intact eggs: a study involving naturally infected hens. Epidemiol Infect 1989;103:415-423
CrossRef | Web of Science | Medline3
de Louvois J . Salmonella contamination of eggs. Lancet 1993;342:366-367
CrossRef | Web of Science | Medline4
Nichols G ,de Louvois J . The microbiological quality of ice cream and other edible ices. PHLS Microbiol Dig 1995;12:11-15
Author/Editor Response
The authors reply:
To the Editor: Dr. O'Ryan questions our estimate of the number of persons in whom S. enteritidis gastroenteritis developed after they ate Schwan's ice cream; he bases his doubts on the underlying variability in the contamination of the ice cream and, in particular, in the distribution of a “hot lot” produced on August 26, 1994. We agree that it is unlikely that all 89 tanker trailers that transported ice cream premix were uniformly contaminated with each load. However, as we noted, our estimate of cases was based on a random survey of 200 households that had Schwan's ice cream delivered between September 10 and September 20 that was not associated with the lot produced on August 26. Thus, contrary to Dr. O'Ryan's interpretation, our findings are generalizable to all consumers of Schwan's ice cream. In fact, since our estimate was independent of the effect of the hot lot produced on August 26, we probably underestimated the number of cases resulting from this outbreak both in Minnesota and nationwide. Other areas of the country that received the August 26 product would most likely have had increased levels of illness similar to those in southeastern Minnesota. However, Schwan's Sales Enterprises, Inc., did not supply the Centers for Disease Control and Prevention with national product-distribution data for our investigation of this outbreak; the lack of such data has prevented us from conducting similar regional analyses in other states.
We would like to thank Djuretic and colleagues for their comments on ice cream and salmonella. The contamination of pasteurized food products and the use of unpasteurized hens' eggs are preventable hazards. Public health officials must work with the food industry and educate consumers to control these hazards and prevent similar outbreaks in the future.
We would also like to correct an oversight: William L. Oemichen, Minnesota Department of Agriculture, St. Paul, should have been included as a member of the Investigation Team.
Thomas W. Hennessy, M.D.
Laurence Slutsker, M.D., M.P.H.
Centers for Disease Control and Prevention, Atlanta, GA 30333Craig W. Hedberg, Ph.D.
Kristine L. MacDonald, M.D., M.P.H.
Michael T. Osterholm, Ph.D., M.P.H.
Minnesota Department of Health, Minneapolis, MN 55440-9441- Citing Articles (1)
Citing Articles
1
A. N. Sheth, M. Hoekstra, N. Patel, G. Ewald, C. Lord, C. Clarke, E. Villamil, K. Niksich, C. Bopp, T.-A. Nguyen, D. Zink, M. Lynch. (2011) A National Outbreak of Salmonella Serotype Tennessee Infections From Contaminated Peanut Butter: A New Food Vehicle for Salmonellosis in the United States. Clinical Infectious Diseases 53:4, 356-362
CrossRef
