Gastroenteritis Outbreak Among Canadian Forces Members: Bosnia-Herzengovina, August 2003

The Canadian Forces (CF) and other NATO militaries have been peacekeeping in Bosnia-Herzegovina for 10 years under the authority of the United Nations Security Council. In August 2003, approximately 1,192 CF members were serving in five Canadian camps (Velika Kladusa, Zgon, Bihac, Glamoc, and Drvar), three multinational locations (Banja Luka, Sipovo, Sarajevo), and two remote communication stations (Gos Peak and Mount Gola). The camp in Zgon had a population of approximately 449 CF members.

Personnel from the CF Unit Medical Station (UMS) provided routine outpatient care, emergency medical care, and short-term inpatient care to deployed CF members and emergency care to contractors with the Department of National Defence at each camp.

On 20 August, 2003, the UMS in Zgon notified the Task Force Surgeon of 38 individuals who had reported with gastroenteritis since 1 August, 2003. Nineteen of the 38 members presented on 19 August, 2003. Additional members were reportedly ill but had not presented to the UMS. Previously, the trend had been one or two gastroenteric illnesses per month. The UMS indicated that its anti-diarrheal medications had been depleted. None of the ill individuals required ospitalization; one patient required overnight observation for intravenous rehydration. On 20 August, 2003, the Task Force Surgeon requested assistance from Force Health protection, Department of National Defence (DND), Canada.

Living conditions

Living quarters for CF members included shared canvas tents called "weather havens", common barracks, and modified sea containers with multiple beds; camps used shared washroom facilities. During field exercises, members slept in shared canvas tents with cots placed inches apart and used outdoor latrines. In camps, meals were taken in a common dining hall (the Mess), where food was served cafeteria-style with several common serving stations (e.g. salad bar, drink dispensers, bread/fruit stations).

All camps had rationed bottled water. Larger camps obtained water from a local municipal well and/or river. Municipal water was chlorinated but because of fluctuating chlorine residuals was considered non-potable. This water was used in the washrooms for toilets, showers and hand washing.

In Zgon, river water contained pollutants from sewage runoff, human bathing, and watering of livestock. A reverse osmosis water purification unit (ROWPU) was used to create potable water. Water, accessed through an intake hose located a metre or so from the shoreline, was strained through a 2000 µm filter. It was pumped to a treatment building for further filtration (ranging from 100 µm to 1.0 µm). Smaller camps without purification systems obtained potable ROWPU water by means of a truck and portable "water buffalo" trailer. The vehicles were monitored and secured.

Methods

The Task Force Surgeon assembled and led a multidisciplinary team to conduct the investigation. Individuals presenting with gastrointestinal symptoms were identified from the outpatient encounter log, and a retrospective chart review was conducted. UMS charts were reviewed for age, sex, date of patient visit, symptom onset and duration, and treatment. A clinical case definition was developed.

Other CF camps (Drvar, Bihac, Gos Peak, Mount Gola, Velika Kladusa, Banja Luka) sharing military duties, vacations/leaves, or common water sources with Zgon were contacted to determine whether they had experienced an increase in gastrointestinal illness. Drvar reported such an increase, and similar data were obtained for these individuals. Zgon shared a secondary water source with the neighbouring town. Therefore, the local civilian hospital was contacted to determine whether there had been an increase in visits for gastrointestinal illness.

Enhanced surveillance, including daily reporting to the Task Force Surgeon, was implemented for all CF camps on 21 August, 2003. In Zgon, active case-finding was conducted. All acutely ill individuals with gastrointestinal illness were requested to report to the UMS for assessment. A standard questionnaire was developed to capture demographic information, symptoms, occupation, sleeping arrangements, water and food consumption, and a travel history. The Mess menu obtained for July and August facilitated food consumption histories. Persons meeting the case definition were interviewed to generate etiologic hypotheses.

Stool samples from several acutely ill individuals were submitted to the Microbiology Laboratory Centre in Zagreb (Croatia) for ova and parasites, culture and sensitivity, and virology testing. The laboratory had virology capabilities to test for adenovirus and rotavirus but not for norovirus.

Environmental assessments in the kitchen included inspection for cleanliness, dishwashing, and proper food storage, preparation and serving practices. Kitchen personnel were interviewed about recent gastrointestinal symptoms. Water samples were collected from the Mess kitchen taps (ROWPU), the "water buffalo" tank (ROWPU), and the washroom taps (non-potable city water). The Mess drink dispensers (water and juice) were also sampled because of previously identified problems with the dispensers.

The Preventive Medicine Technician used the Millipore (Billerica, Mass.) paddle/membrane filter technique to test for the presence or absence of total fecal coliforms and to obtain heterotrophic bacterial counts. The ROWPU treatment facility was inspected for potential system failure, and a record audit was conducted for chlorine levels and bacterial counts for the previous 6 months.

Results

Case definition

A case was defined as any CF member or civilian employee in Zgon or Drvar who became ill with vomiting and/or diarrhea (three or more loose watery stools in a 24-hour period) and presented to the UMS after 1 August, 2003.

Descriptive epidemiology

Between 1 August, 2003, and 1 September, 2003, 139 cases of gastrointestinal illness were identified among all CF camps. There were 115 cases, 96 in Zgon and 19 in Drvar; attack rates were 21% (96/449) and 11% (19/170) respectively. The local civilian hospital near Zgon did not report an increase in gastrointestinal illness during this period. The epidemic curve (Figure 1) revealed an irregular pattern with small peaks every 2 to 3 days and a larger peak on 19 August, 2003, midway through the outbreak. The epidemic curve suggested predominantly person-to-person transmission.

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Figure 1. Epidemic curve of gastroenteritis cases:CampZgon andDrvar (Bosnia-Herzegovina) , 1 August to 1 September, 2003 (n = 115)

In Zgon, the sex-specific attack rates were lower among men, at 21% (84/409), than women, 30% (12/40). Drvar had a small female population (n = 9) with no cases; all the cases were male with an attack rate of 12% (19/161). The mean age of the cases in both camps was 28 years (range: 19 to 43 years).

Duration of illness was known for 20 cases, and the mean was 4.5 days (range: 2 to 9 days). The most commonly reported symptoms were diarrhea, abdominal cramping, nausea, headache, chills, and vomiting (Table 1). In Zgon, 16.7% (16/96) of cases experienced vomiting and diarrhea, whereas in Drvar only one case experienced both. One case reported bloody stool, likely attributable to severe prolonged symptoms, and one case required overnight observation in the UMS for intravenous rehydration. There were no hospitalizations and no deaths.

In Zgon, cases were mapped by sleeping location and onset date. Most cases clustered in four "weather havens" housing transport personnel, the armoured vehicle group, and the combat engineer regiment. Seventy-two percent (69/96) of cases indicated that they had had close contact (e.g. worked or roomed) with other ill individuals. In Drvar, 52.6% (10/19) of cases roomed in common barracks.

CF members from Zgon and Drvar frequently worked and travelled together. Leave-related travel during July and August was reported for 53.1% (52/94) of Zgon cases and 56.8% (7/19) of Drvar cases. Common destinations were Split and Maribor (Croatia), Italy, Spain, and Canada.

The main water sources for consumption and brushing of teeth were bottled (96.5%) and ROWPU (47.4%) water among Zgon cases. Three-day food histories taken from Zgon cases did not implicate any food items, and no food samples were obtained.

Table 1. Clinical symptoms of gastroenteritis cases by Canadian Forces camp

Symptoms	Zgon, n=96		Drvar, n=19		Total*
	Yes n (%)	No n (%)	Yes n (%)	No (%)	Rate n (%)
Diarrhea	95 (99.0%)	1 (1.0%)	19 (100%)	0%	114/115 (99.1%)
Cramping	82 (85.4%)	12 (12.5%)	10 (52.6%)	2 (10.5%)	92/106 (86.8%)
Headache	46 (47.9%)	36 (37.5%)	3 (15.8%)	9 (47.4%)	49/94
Nausea	45 (46.9%)	47 (49.0%)	11 (57.9%)	1 (5.3%)	56/104 (53.9%)
Chills	28 (29.0%)	48 (50.0%)	1 (5.3%)	11 (57.9%)	29/88 (33.0%)
Muscle ache	23 (24.0%)	31 (32.3%)	N/A n/d	N/A n/d	23/54 (43.0%)
Vomiting	17 (17.7%)	72 (75.0%)	1 (5.3%)	11 (57.9%)	18/101 (17.8%)
Diarrhea and vomiting**	16 (16.7%)	72 (76.6%)	1 (5.3%)	11 (57.9%)	17/100 (17.0%)
Bloody stool	1 (1.0%)	95 (99.0%)	0 (0.0%)	19 (100%)	1/115 (0.8%)
* Denominators vary because of missing / unknown symptoms data. ** Not mutually exclusive

Of the stool samples obtained from 18 acutely ill cases, 94.4% (17/18) tested negative for ova and parasites, and adeno/rotavirus. One case positive for adeno/rotavirus had recurrent gastroenteric symptoms over 2 months. Culture and sensitivity results were negative for all but one sample, which was positive for Salmonella.

Environmental assessment

Kitchen/food: Early in the investigation, a kitchen worker underwent a routine "end of rotation" medical examination and submitted a stool sample that tested positive for Giardia lamblia. Despite acute gastrointestinal symptoms the individual continued to work. On 22 August, 2003, the individual was temporarily restricted from work duties until treatment had been completed and follow-up stools tested negative. No other staff member reported illness.

No violations were found in cleaning, food storage, food preparation or serving practices. Local food was not purchased or consumed except in special circumstances. All food supplied to the kitchen was purchased from a reputable European wholesaler.

Water treatment: The ROWPU process was investigated on 23 August, 2003, to rule out system failure. The filters worked properly and were well maintained. The conductivity meter measuring the removal of particulates from raw to filtered water had recently undergone calibration and was within normal limits.

Routine bacterial testing was conducted weekly from the kitchen taps, washroom taps, transport trucks, and water buffalo. Chlorination levels were taken daily and reported monthly. All residual chlorine levels were within normal limits ( = 0.2 ppm), and no bacteria were cultured during the months of July and August 2003.

Residual chlorine levels for the four trucks supplying ROWPU water to Drvar, Gos Peak, and Mount Gola were routinely verified before leaving Zgon. These logs were reviewed and found to be within normal limits ( = 0.4 ppm).

Laboratory findings: On 22 August, 2003, four drink dispensers (water and juice) in the Mess were sampled for bacterial analysis: coliform growth was found in the orange juice drink dispenser despite repeated cleaning and staff education. The dispenser was taken out of service until it no longer tested positive for total coliform bacteria.

On 24 August, 2003, water samples obtained from the Mess kitchen taps (potable ROWPU water), water buffalo tanks (potable ROWPU water), and the washroom taps (non-potable city water) all tested negative for bacteria (fecal coliform or Escherichia coli).

Prevention and control measures

On 22 August, 2003, a boil water advisory was issued because of uncertainty regarding the water filtration capability, chlorination levels, and the kitchen worker's stool sample positive for Giardia lamblia. Other prevention and control measures included the following:

• temporary restriction of cases from duty until symptom-free for 48 hours;
• case confinement to sleeping quarters;
• provision of meals in quarters;
• segregation of cases to specified washroom facilities;
• enhanced cleaning in common areas (e.g. washrooms, computer areas, pay phones, Mess, gym);
• improved hand washing supplies and signage;
• enforced hand washing for all CF members entering the Mess hall;
• re-education of kitchen personnel about proper food handling;
• reduced self-serve stations and elimination of finger foods. The outbreak ended 2 weeks after prevention and control measures had been implemented.

Discussion

Zgon and Drvar camps experienced a high rate of gastrointestinal illness in August 2003. Epidemiologic and environmental investigations were carried out but were unable to identify either the source of infection or the causative agent. The symptoms, short illness duration, and person-to-person transmission pattern are suggestive of a viral causative agent. The negative results for ova and parasites, and culture and sensitivity further support this hypothesis. The clinical and epidemiologic features of the outbreak were consistent with norovirus, but testing for this organism was not available in Zagreb. While some specimens did test positive for giardia, adeno/rotavirus or salmonella species, these appeared to be sporadic occurrences.

One limitation of our investigation was the lack of bottled water testing. However, epidemiologic results were suggestive of person-to-person transmission and not a point source or common source outbreak. Another limitation was the descriptive study design. A case control study might have identified specific risk factors associated with transmission, but this was not carried out for the following reasons: the descriptive epidemiology, laboratory, and environmental findings identified norovirus as the likely agent; the investigation encountered logistical challenges; and the prevention and control measures that were implemented had a rapid impact. Logistical challenges also impeded our ability to quantify the duration of illness and the overall impact on troop strength (e.g. work days lost).

Norovirus outbreaks are common in many types of settings (community, hospital, cruise ships) and notoriously difficult to prevent and control^(1-3). This is also particularly true of military environments ⁽⁴⁾. British and US investigations have identified that the lack of sanitation in military training and deployment operations⁽⁴⁾, close living conditions^(4-7), common eating areas/food sources⁽⁸⁾, and contaminated drinking water⁽⁹⁾ have all contributed to sporadic gastrointestinal illness and outbreaks.

Many cases in our investigation reported close contact with other ill individuals. The dynamic nature of the Bosnia-Herzegovina deployment, crowded sleeping conditions, and mixing of camp personnel during work and leave likely contributed to the transmission of the illness within and between the camps. Education regarding good personal hygiene and public health practices should be reinforced before and during deployment.

Although the number of work days lost could not be calculated, like other investigations the attack rates (21% in Zgon and 11% in Drvar) demonstrate the potential impact of gastrointestinal illness on troop strength, routine military operations, and health care resources^(4,7,10). Military health care professionals need to understand and use health surveillance systems to monitor health events within the population served. This should facilitate early detection of gastroenteritis outbreaks, which can aid in identifying and removing the outbreak source and promote prompt prevention and control measures to reduce the number of ill members.

Conclusion

In August 2003, CF members deployed to Bosnia-Herzegovina experienced an outbreak of gastroenteritis. No causative organism was identified, but a viral agent, likely norovirus, was suspected. Prompt implementation of prevention and control measures, with support from the operational chain of command, aided the cessation of the outbreak within 2 weeks. Deployed operations require military personnel to live in close quarters, which creates an ideal environment for the transmission of communicable disease. Enhanced personal hygiene, attention to good public health practices, and close monitoring of disease trends must be emphasized during pre-deployment training and throughout operations to prevent and contain infectious disease outbreaks.

Acknowledgements

The authors would like to thank the following for their assistance with this investigation: Capt D. Scott, MD, CFB Winnipeg, MB; Warrant Officer (WO) D. Hort, Canadian Forces Health Services Centre (A) Halifax, NS; WO S. Cunningham, Canadian Forces Medical Services School Borden, ON; Master Sergeant M. Boucher, CFBWinnipeg, MB; Private G. Turcott, CFB Edmonton, AB; Task Force Bosnia-Herzegovina Roto 12 UMS personnel at Zgon and Drvar; Microbiology Laboratory Centre Zagreb, Croatia; Dr. M. Carew, Directorate of Force Health Protection, DND, Ottawa, ON; and Drs. L. Panaro and L. Lior, Canadian Field Epidemiology Program, Public Health Agency of Canada, Ottawa, ON.

References

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8. Centers for Disease Control and Prevention. Outbreak of acute gastroenteritis associated with Norwalk-like viruses among British military personnel ? Afghanistan, May 2002. JAMA 2002;287(24):3202-4.

9. Warner RD, Carr RW, McCleskey FK et al. A large nontypical outbreak of Norwalk virus: Gastroenteritis associated with exposing celery to nonpotable water and with Citrobacter fereundii. Arch Intern Med 1991;151(2):2419-24.

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Source: J Wilson, BScN, MHSc, Canadian Field Epidemiology Program, Public Health Agency of Canada; B Strauss, RN, MSc, and Commander I Fleming, MD, MHSc, Directorate of Force Health Protection, DND; Sergeant T Schulz, Canadian Forces Base Shilo, MB; and M Tepper, MD, FRCPC, Directorate of Force Health Protection, DND.

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