Infectious Diarrheal Outbreaks in the Israeli Military, 1988-2002

Military Medicine, Jul 2005 by Schwaber, Mitchell J, Grotto, Itamar, Balicer, Ran D, Davidovitch, Nadav, Et al

We analyzed 865 diarrheal outbreaks with an identified bacterial pathogen or unknown cause that occurred in the Israeli military between 1988 and 2002. The number of outbreaks per year declined over the study period, as did the proportion of outbreaks with an identified pathogen. Shigella, Salmonella, and Staphylococcus species were the bacteria most commonly isolated. Seventy percent of the outbreaks involved 100 cases. More than one-half of the outbreaks occurred in field units, but these outbreaks were smaller than those in other units. The most commonly identified cause of the outbreaks was a lapse in maintaining standards of food preparation. Improvements in infrastructure and enhanced attention to surveillance, education, and infection control have resulted in a marked decline in the number of outbreaks in recent years.

Introduction

Infectious diarrhea remains a significant health problem. In the United States, the annual incidence of food-borne illness is estimated at 76 million cases, accounting for 325,000 hospitalizations and 5,000 deaths each year.1 Diarrheal outbreaks can lead to considerable morbidity, lost workdays, and significant economic costs.2 In the military, such outbreaks have been known to incapacitate large numbers of soldiers in active duty units such as flight staffs,3 naval crews,4 and soldiers on training bases.5 Risk factors for diarrheal outbreaks in military units are crowded living conditions, substandard personal and unit hygiene practices, mass food processing facilities, lack of adequate refrigeration under field conditions, and frequent movement of personnel among units and throughout various geographic locations.2

During World War II, as well as the Korean and Vietnam Wars, diarrhea was the primary morbidity associated with infectious diseases.2 More recently, large outbreaks have been reported among U.S. forces operating in the Persian Gulf,6 Egypt,7 Somalia,8 and Thailand.9 Diarrheal outbreaks and cases of food poisoning have been described for other armies as well, throughout Europe, Africa, and the Middle and Far East.2,9-11

Within the Israel Defense Forces (IDF), infectious diarrhea, involving sporadic illness and outbreaks, remains a public health problem. The last large-scale description of the epidemiological characteristics of food-borne outbreaks in the IDF was reported by Grotto et al.2 Summarizing data from 1978 to 1995, the authors found that the overall incidence of outbreaks, which was highest in the late 1980s, was lowest in the last 2 years of their study. The number of soldiers involved in any given outbreak declined during the study period. Shigella species were the most common pathogens isolated, followed by Salmonella species. Most outbreaks were small; almost three-quarters involved 100 soldiers. Outbreaks in which a causative agent was identified tended to be larger than those without an isolated pathogen, and those occurring on training bases were larger than those on field bases.

The purpose of the current report was to summarize and characterize diarrheal outbreaks in the Israeli military from 1988 to 2002. We aimed to examine features similar to those explored by Grotto et al.2 and to determine whether the trends they reported as of 1995 have continued. We also aimed to determine risk factors for outbreaks, as well as common causes and implicated pathogens, to arrive at strategies for prevention.

Methods

This study was a retrospective analysis of epidemiological and microbiological data gathered by the IDF Medical Corps Army Health Branch, representing all reported outbreaks of diarrhea in the Israeli military between 1988 and 2002 that had either an identified bacterial cause or no known cause. Military regulations mandate reporting of all suspected outbreaks of gastroenteritis in a military unit. A suspected outbreak is declared when at least five soldiers in a single unit develop diarrhea within one 24-hour period or when eight or more soldiers develop diarrhea within a 48-hour period. Epidemiological investigation is required when an outbreak has been confirmed on the basis of one of the following definitions: (a) ≥10 soldiers in a single unit develop diarrhea in a single day; (b) ≥ 15 soldiers in a single unit develop diarrhea within a 2-day period; or (c) 25% of the personnel in a single unit develop diarrhea within a 7-day period.

Epidemiological investigation of diarrheal outbreaks in the IDF includes collection of the following information: (a) information on the outbreak, including case definition, number of affected soldiers, number of referrals to the unit clinic, and gender, type of service, and date and time of symptom onset for each patient; (b) characteristics of the illness, including clinical features of the illness (e.g., fever, abdominal pain, nausea, and vomiting) and characteristics of stool (e.g., accompanied by blood or mucus); (c) site inspection by hygiene officers, including the kitchen and other areas within the unit, personal hygiene status of food handlers, results of food handlers' periodic stool cultures, and investigation of all food items consumed in the unit during the 48 hours preceding the onset of the outbreak; and (d) laboratory tests, including bacterial cultures of drinking water and food items (samples of all items served in mess halls are routinely retained by the kitchen staff for 48 hours, for this purpose). Stool cultures from affected soldiers and all food handlers are routinely cultured for Shigella, Salmonella, and Campylobacter. Polymerase chain reaction testing for enterotoxigenic Eschenchia colt has been available since 1996 for use in outbreaks characterized by a high degree of clinical and epidemiological suspicion for this pathogen.