Epidemiologic Notes and Reports Multistate Outbreak of Salmonella poona Infections -- United States and Canada, 1991

During June and July 1991, more than 400 laboratory-confirmed infections with Salmonella poona occurred in 23 states (Figure 1) and in Canada. This report describes several investigations that indicated this was a large nationwide outbreak related to consumption of cantaloupes. UNITED STATES Illinois and Michigan

During June and July, laboratories in Illinois and Michigan identified 49 cases of S. poona infection for which onset of illness had occurred during the first 3 weeks of June. Symptoms included nausea, vomiting, diarrhea, abdominal cramps, and fever; the duration of symptoms was 3-12 days. A case-control investigation compared culture-confirmed cases with age- and residence-matched controls using the same questionnaire in both states; nine (28%) of 32 ill persons and three (7%) of 45 controls specifically recalled consuming cantaloupe in fruit salad (odds ratio (OR)=5.9; 95% confidence interval (CI)=1.3-36.1); 14 (44%) of 32 ill persons and 18 (38%) of 48 controls recalled eating cantaloupe during the 3 days before onset of symptoms (OR=2.6; 95% CI=0.9-7.7). Seventeen S. poona outbreak isolates from seven states were characterized by the Michigan Department of Public Health Laboratory. Chromosomal digest by low-frequency cutting restriction endonuclease and pulse field gel electrophoresis revealed an identical pattern, suggesting a probable common origin.

Industry sources reported that the temporal and geographic distributions of cases were compatible with distribution of cantaloupe to the affected states from the Rio Grande region of Texas from mid-May to mid-June. Minnesota

During June and July, 20 S. poona isolates were identified by the Minnesota Department of Health, Division of Public Health Laboratories, an increase from 1989 and 1990 when four S. poona isolates per year were reported. Onset of symptoms occurred from June 5 through July 7; eight cases occurred during the week of June 10-16.

In a case-control study of the first 13 cases and 26 age- and telephone-exchange-matched controls, eight (62%) ill persons and no controls reported consuming cantaloupe from a salad bar or in a fruit salad (OR=undefined; p less than 0.01). Illness was not associated with consumption of fresh sliced cantaloupe (OR=2.6; 95% CI=0.5-15.2).

Grocery stores, restaurants, and distributors reported that the implicated cantaloupes were from Texas. Industry sources identified the probable source of these cantaloupes as an area including Hidalgo and Starr counties in the lower Rio Grande Valley of Texas. Distribution of onset of illness coincided with the shipping of cantaloupes from this area from May 10 through June 15. New Jersey

During June, 17 S. poona isolates were identified in New Jersey. Onset of illness ranged from May 20 to June 26. Two isolates were identified from among the 75 attendees at a June 9 party. Food histories were obtained from 38 attendees; 17 (45%) were ill with diarrhea. Analysis of these histories associated illness with eating a fruit salad served at the party (OR=6.2; 95% CI=1.2-41.9; p=0.03). The fruit salad contained cantaloupe, honeydew melon, watermelon, strawberries, grapes, and pine apples. The suppliers of the party caterer reported that they received cantaloupes from Arizona, California, and Texas. CANADA

As of July 24, 72 laboratory-confirmed cases of S. poona had been reported to the Laboratory Centre for Disease Control, Health and Welfare Canada--66 (92%) from Ontario and the remainder from Newfoundland, Quebec, and Saskatchewan. Since 1969, three to 18 human isolates of this serotype have been reported annually in Canada. Most cases occurred in the second and third weeks of June. A case-control study to examine vehicles of infection is in progress.

Reported by: BJ Francis, MD, State Epidemiologist, Illinois Dept of Health. JV Altamirano, MD, MG Stobierski, DVM, W Hall, MD, B Robinson, PhD, S Dietrich, MS, R Martin, DrPH, F Downes, DrPH, KR Wilcox, Jr, MD, State Epidemiologist, Michigan Dept of Health. C Hedberg, MS, R Wood, MD, M Osterholm, PhD, State Epidemiologist, Minnesota Dept of Health. C Genese, MBA, MJ Hung, MS, S Paul, MD, KC Spitalny, MD, State Epidemiologist, New Jersey Dept of Health. C Whalen, MD, J Spika, MD, Laboratory Centre for Disease Control, Health and Welfare Canada. Div of Emergency and Epidemiological Operations; Center for Food Safety and Applied Nutrition, Food and Drug Administration. Enteric Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note:

Salmonella is the most frequently reported cause of foodborne outbreaks of gastroenteritis in the United States (1). Foods containing poultry or other meat, eggs, or dairy products are most often the vehicles for foodborne salmonellosis. Food-preparation practices contributing to past outbreaks include improper food storage or holding temperature and poor hygiene by foodhandlers (1). Fruits and vegetables are not often identified as vehicles for Salmonella infection; however, in 1990, two multistate outbreaks of salmonellosis associated with fruits and vegetables occurred: S. chester associated with canteloupes affected at least 245 persons in 30 states, and S. javiana gastroenteritis associated with tomatoes affected 174 persons in four states (2,3).

In this report, the association of illness with consumption of cantaloupe in fruit salads or from salad bars suggests that contaminated fruit may have incubated for several hours at room temperature after preparation. In neither this outbreak nor the two Salmonella outbreaks in 1990 (2,3) was the organism recovered from an implicated fruit or vegetable; most of the produce was consumed or discarded before the investigation.

It is difficult to trace melons once they are unpacked from crates. Although industry sources identified the lower Rio Grande Valley in Texas as the probable source of the implicated cantaloupes, some may have come from Mexico. The Food and Drug Administration (FDA) sampled imported cantaloupes and watermelons at the U.S. border in 1990 and 1991 and isolated many serotypes of Salmonella from approximately 1% of the rinds. Grown on the ground, melons may be contaminated on their surface with dirt, chemicals, animal excreta, or bacteria, including Salmonella. Although large produce companies wash and dip melons in a chlorine solution, field-packed melons do not receive such treatment. Cutting an unwashed melon through a contaminated rind may lead to contamination of the edible part via the cutting knife or subsequent contact of dirty rinds with cut pieces of melons. Excessive time at room temperature may then permit bacterial growth.

To reduce the risk for S. poona infection from melons, the FDA recommends that both produce retailers and consumers thoroughly clean melons with potable water before cutting them, prepare cut melons using clean and sanitized utensils and surfaces, hold cut melons at less than or equal to 45 F (less than or equal to 7 C) until served or sold, and limit display of cut cantaloupes to less than 4 hours if not kept refrigerated. To decrease the risk for Salmonella food poisoning, it is prudent to wash all fruits and vegetables before they are handled and consumed.

References

1. CDC. Foodborne disease outbreaks, 5-year summary, 1983-1987. In: CDC surveillance summaries, March 1990. MMWR 1990;39(no. SS-1):15-57.

2. Ries AA, Zaza S, Langkop C, et al. A multistate outbreak of Salmonella chester linked to imported cantaloupe (Abstract). In: American Society for Microbiology. Program and abstracts of the 30th Interscience Conference on Antimicrobial Agents and Chemotherapy. Washington, DC: American Society for Microbiology, 1990:238.

3. Wood RC, Hedberg C, White K, et al. A multi-state outbreak of Salmonella javiana infections associated with raw tomatoes (Abstract). In: CDC. Epidemic Intelligence Service 40th Annual Conference. Atlanta: US Department of Health and Human Services, Public Health Service, 1991:69.

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