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Plesiomonas shigelloides and Salmonella serotype Hartford Infections Associated with a Contaminated Water Supply -- Livingston County, New York, 1996

On June 24, 1996, the Livingston County (New York) Department of Health (LCDOH) was notified of a cluster of diarrheal illness following a party on June 22, at which approximately 30 persons had become ill. This report summarizes the findings of the investigation, which implicated water contaminated with Plesiomonas shigelloides and Salmonella serotype Hartford as the cause of the outbreak.

The party was held at a private residence on June 22 and was attended by 189 persons. Food was provided by a local convenience store that sells gasoline, packaged goods, sandwiches, and pizza and prepares food for catered events. The convenience store had not catered any parties during the preceding 5 days but catered two parties on June 23. LCDOH contacted the organizers of these events and found no other reports of illness.

To determine the source and extent of the outbreak and mechanism of contamination, LCDOH conducted a cohort study, an environmental investigation, and micro-biologic examinations of stool specimens, leftover food items, and water samples. A menu and guest list were obtained and guests were interviewed by telephone. A probable case was defined as diarrhea (greater than 3 loose stools during a 24-hour period) in a person who attended the party and became ill within 72 hours. Persons with a confirmed case had either Plesiomonas shigelloides or Salmonella serotype Hartford or both isolated from stool. The caterer and facility employees were interviewed to obtain information on food preparation, and the water source was inspected.

Of the 189 attendees, 98 (52%) were interviewed. Sixty persons reported illness; 56 (57%) of 98 respondents had illnesses meeting the case definition. The mean age for case-patients was 41 years (range: 2-85 years), and 32 (57%) were male. Stool specimens were obtained from 14 ill attendees: nine yielded only P. shigelloides, three only Salmonella serotype Hartford, and two had both organisms. One person with culture-confirmed Salmonella serotype Hartford was hospitalized. The clinical profiles of the culture-confirmed (n=14) and probable (n=42) cases were similar.

Twenty food and beverage items were served at the party. Three food items were associated with illness: macaroni salad, potato salad, and baked ziti. Of 56 attendees who ate macaroni salad, 43 (77%) became ill, compared with 17 (40%) of 42 who did not eat macaroni salad (relative risk {RR}=2.6; 95% confidence interval {CI}=1.5-4.4). Of 49 guests who ate potato salad, 36 (73%) became ill, compared with 20 (44%) of 45 who did not eat potato salad (RR=2.1; 95% CI=1.2-3.6). Of 46 attendees who ate baked ziti, 36 (78%) became ill, compared with 20 (42%) of 48 that did not eat baked ziti (RR=2.7; 95% CI=1.5-4.9).

Leftover food samples of these three items were collected on June 25 and sent for microbiologic examination. Salmonella serotype Hartford was isolated from the macaroni salad and baked ziti. Both Salmonella serotype Hartford and P. shigelloides were isolated from the potato salad. Escherichia coli was isolated from a water sample collected on June 27 from the tap in the store. Water samples collected on July 8 from the well that supplied water to the store contained both Salmonella serotype Hartford and P. shigelloides.

Preparation of the salads and the baked ziti began on June 21, and prepared food items were stored in a walk-in cooler overnight. On June 22, the ziti was prepared by heating the tomato sauce, pouring it over the meat and pasta, and heating in an oven for 50 minutes at an unknown temperature. The ziti remained in the oven with the heat off until it and the salads were transported to the party.

All foodhandlers denied gastrointestinal illness with onset before June 22. However, three foodhandlers reported illness beginning after June 22; all three reported having eaten foods prepared for the party. P. shigelloides was recovered from stool specimens from these three workers only.

The New York State Department of Agriculture and Markets found nine sanitary violations at the caterer's facilities. The water source, an unprotected dug well approximately 10 feet deep, served only the store. The well was fed by shallow ground water and may have received surface runoff from surrounding tilled and manured farm land and water from adjacent streams. A small poultry farm was located approximately 1600 feet upstream of the well. Farm field drainage systems discharged into the source water stream just above the well. A water sample collected at the store on June 27 showed no chlorine residual, indicating that the pellet chlorinator was off-line at the time of the event. The pellet chamber was empty and the system did not contain any filtration mechanism. Well water used for food preparation (i.e., rinsing pasta used in salads, mixing ingredients, cooking food items, and cleaning equipment) was probably contaminated as a result of rainfall on June 19 and June 20 that transported pathogens from the surrounding farmland. The improperly maintained chlorinator allowed these pathogens to reach the food preparation area. After the outbreak, the store was prohibited from preparing food until an adequate water-treatment system that met drinking water standards could be provided. Store employees and the public were instructed not to drink the water.

Reported by: R Van Houten, D Farberman, J Norton, J Ellison, Livingston County Dept of Health, Mt. Morris; J Kiehlbauch, PhD, T Morris, MD, P Smith, MD, State Epidemiologist, New York State Dept of Health. Foodborne and Diarrheal Diseases Br, Div of Bacterial and Mycotic Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The findings in this report implicated a deficient water supply system as the cause of an outbreak of diarrheal illness caused by Salmonella serotype Hartford and P. shigelloides. Unfiltered, untreated surface water led to contamination of food during its preparation.

Most infections with P. shigelloides have been associated with drinking untreated water, eating uncooked shellfish, or with travel to developing countries (1-3). P. shigelloides (previously Aeromonas shigelloides) are ubiquitous, facultatively anaerobic, flagellated, gram-negative rods (3). Although they are widespread in the environment, few waterborne or foodborne outbreaks have been reported (4). P. shigelloides have been isolated from a variety of sources, including wild and domestic animals (2). Infection is characterized by self-limited diarrhea with blood or mucus, abdominal cramps, and vomiting or fever (5). Symptoms usually occur within 48 hours of exposure. Fecal leukocytes and erythrocytes have been found on stool smears (1); however, the exact mechanism of the diarrhea (secretory versus inflammatory) is unknown.

Salmonella serotype Hartford is a rare serotype that has been isolated from porcine and bovine sources. In May 1995, freshly squeezed, unpasteurized commercial orange juice was implicated as the cause of an outbreak (6). Contamination was thought to have originated from inadequate sanitization of the exterior surfaces of oranges.

In this outbreak, the well water most likely became contaminated with both P. shigelloides and Salmonella serotype Hartford through runoff from nearby farms. The outbreak could have been prevented if effective public health measures had been in place. Routine testing of well water for total fecal coliform bacteria, turbidity, and chlorine residual may enable early detection of fecal contamination and rapid decontamination. Filtration and chlorination of potable water systems have substantially reduced waterborne outbreaks and subsequent morbidity and mortality. Where possible, water sources subject to contamination from agricultural runoff should not be used for drinking or food preparation. Disinfection and filtration of water from any source can further reduce the risk for waterborne illness.


  1. Soweid AM, Clarkston WK. Plesiomonas shigelloides: An unusual cause of diarrhea. Am J Gastroenterol 1995;90:2235-6.

  2. Jeppesen C. Media for Aeromonas spp., Plesiomonas shigelloides and Pseudomonas spp. food and environment. Int J Food Microbiol 1995;26:25-41.

  3. San Joaquin VH. Aeromonas, Yersinia, and miscellaneous bacterial enteropathogens. Pediatr Ann 1994;23:544-8.

  4. Schofield GM. Emerging foodborne pathogens and their significance in chilled foods. J Appl Bacteriol 1992;72:267-73.

  5. Holmberg SD, Wachsmuth IK, Hickman-Brenner FW, Blake PA, Farmer JJ. Pleisiomonas enteric infections in the United States. Ann Intern Med 1986;105:690-4.

  6. Cook KA, Swerdlow D, Dobbs T, et al. Fresh-squeezed Salmonella: an outbreak of Salmonella Hartford associated with unpasteurized orange juice -- Florida {Abstract}. EIS Conference Abstract 1996;38-9.

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