Epidemiologic Notes and Reports Viral Gastroenteritis -- South Dakota and New Mexico

The following reports describe two outbreaks of viral gastroenteritis associated with contaminated water.

South Dakota. An outbreak of diarrhea occurred among the 331 participants in an outing held at a South Dakota campground on August 30 and 31, 1986. During the event, in which participants hiked 10 or 20 km, water and a reconstituted soft drink were available at rest stands. The State Department of Health conducted a survey of 181 participants: 135 (75%) of these persons reported a gastrointestinal illness. Symptoms most frequently reported were diarrhea (69%), explosive vomiting (55%), nausea (49%), headache (47%), abdominal cramping (46%), and fever (36%). None of the participants required hospitalization. Attack rates by sex and age of patients were virtually equal. Onset of illness occurred 35 hours (mean) after arrival at the campground, and duration of illness was about 33 hours.

A biotin-avidin immunoassay performed at CDC yielded a fourfold rise in antibody titer to Norwalk virus in seven of 11 paired human serum specimens. No pathogenic bacterial or parasitic agents were identified from stool samples. Illness was strongly associated with the consumption of water or the reconstituted powdered soft drink made with water. No other foodstuffs were implicated. The implicated water came from a well at the campground. A yard hydrant was located next to a septic dump station, where sewage from self-contained septic tanks and portable toilets in the park was collected. Water from this hydrant had been used to fill water coolers and to prepare the powdered soft drink. Laboratory analyses of remaining water and reconstituted soft drink samples showed bacterial contamination (fecal coliforms greater than 1,600 cfu/100 mL). Chlorine was stored in a tank and then drawn directly into the water system by a pump without a monitoring system. Water samples obtained from various locations in the campground had excess coliforms when the chlorination system was not operating. Fluorescent dye injected into a 5,000-gallon septic tank situated uphill from the well confirmed that the well was contaminated with sewage.

This campground was closed immediately and voluntarily by the owner. Corrective measures included relocating the well, installing an alarm system to detect malfunctions in the chlorination system, reconstructing the chlorination system to ensure that chlorine remains in contact with water in a storage tank for 30 minutes before the water is distributed, maintaining a daily log on chlorine residuals and sample collection points, and posting the yard hydrant as a nonpotable source of water.

New Mexico. An outbreak of gastroenteritis occurred among the 92 guests and staff at a cabin lodge in northern New Mexico over the Labor Day weekend in 1986. The guests arrived Friday, August 29, and provided their own food for the weekend. The first persons to become ill developed diarrhea on Saturday morning, within 24 hours after arrival. By Wednesday, 36 of the guests and staff members reported symptoms: 34 had diarrhea; 9, vomiting; 14, fever; 22, abdominal cramps; and 1, bloody stools. There were no deaths or hospitalizations.

A questionnaire was administered to all 92 guests and staff to ascertain risk factors for gastroenteritis. Guests consisted of unrelated groups, and they stayed in 18 separate cabins. All 36 of the patients and 37 of the 56 unaffected attendees had drunk water at their cabin. A dose-response relationship was demonstrated between the amount of water consumed and the attack rate. No illness occurred among the persons who did not drink water; 33% of those drinking 1-2 cups and 59% of those drinking greater than or equal to3 cups became ill. Five of the 18 cabins were unaffected; three of these belonged to families who were residents or frequent visitors at the lodge.

Assuming guests were exposed upon arrival or when they first drank water, the median incubation period was 41 hours (range = 7-110 hours). Symptoms lasted from 2-17 days, with a median of 5 days.

The cabins were supplied with water taken from a stream and processed through a small chlorinator and a storage tank that was periodically iodized. A filter had been removed recently from the pipe because it repeatedly became plugged with debris. A severe rainstorm occurred the evening the guests arrived, resulting in increased water turbidity.

Water samples taken at the cabins and the surface stream that supplied the cabins were positive for total coliforms and fecal coliforms. Stool samples from ill patrons were negative for pathogenic bacteria and parasites, except for one sample, from which Giardia was isolated. Convalescent-phase sera were submitted to CDC for 13 cases and 26 controls (2 per case), matched for age within 5 years, gender, and city of residence. Controls were selected from health department personnel who had not visited the lodge. No difference in Norwalk titers was found between five cases and five controls.

Under the supervision of state environmentalists, the water system was renovated before the lodge reopened, with particular emphasis on filters, the chlorinator, and the storage tank. Reported by: PA Bonrud, MS, AL Volmer, TL Dosch, W Chalcraft, D Johnson, B Hoon, M Baker, KA Senger, State Epidemiologist, South Dakota State Dept of Health. CF Martinez, TO Madrid, MPA, RM Gallegos, MS, SP Castle, MPH, CM Powers, JA Knott, RM Gurule, MS Blanch, LJ Nims, MS, PW Gray, PA Gutierrez, MS, M Eidson, DVM, MV Tanuz, HF Hull, MD, State Epidemiologist, New Mexico Health and Environment Dept. Respiratory and Enteroviral Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: The two outbreaks of gastroenteritis described above are representative of those frequently reported to CDC. They demonstrate the need for an improved, specific laboratory approach to identify the agents (many of which are presumed to be viral) responsible for these outbreaks (1,2). Transmission of these viruses is often associated with fecal contamination of water sources used for drinking, swimming, or producing ice (3). Additionally, the contamination of coastal water poses a special problem, since the consumption of seafood is a risk factor for acquiring Norwalk agent infection and other enteric viral agents.

The two best-known enteric viral agents, rotavirus (group A) and Norwalk agent, were first seen in the stools of diarrhea patients by means of electron microscopy in the early 1970s. Both agents have proven to be important causes of gastroenteritis in this country, with rotavirus being the most common agent for diarrhea in young children (4) and Norwalk agent being common in adults (5). In recent years, enteric adenoviruses, non-group A rotavirus, and several 27- to 32-nm enteric viruses, including other Norwalk-like agents, caliciviruses, astroviruses, and other enteric viral pathogens, reportedly have been associated with gastroenteritis (1,6). Recent advances in identifying and diagnosing some of these viruses should make it possible to reduce the number of undiagnosed outbreaks in future investigations. Methods for serologic and antigenic tests are available for some agents, but the examination of stool samples by electron microscopy offers the possibility of identifying agents for which no specific tests are available. The probability of detecting viral particles by electron and diagnosing some of these viruses should make it possible to reduce the number of undiagnosed outbreaks in future investigations. Methods for serologic and antigenic tests are available for some agents, but the examination of stool samples by electron microscopy offers the possibility of identifying agents for which no specific tests are available. The probability of detecting viral particles by electron microscopy is greatest if stool specimens are collected during the early stages of illness, preferably within 12 hours and no later than 48 hours after onset. Some viral particles may be more stable if stool samples are stored at 4 |SDC. The following guidelines are currently recommended for specimen collection specifically for diagnosing outbreaks of viral gastroenteritis.

1. Stool specimens should be collected in bulk volume as soon after the time of disease onset as possible and no later than 48 hours after the onset of symptoms.

2. Stool specimens should be refrigerated, not frozen, and shipped to the laboratory on the same day that the specimen is collected.

3. Paired serum specimens that are collected within 1 week of the disease onset (acute phase) and 3 to 4 weeks after the onset of symptoms (convalescent phase) from both ill patients and controls are required to establish the causal association between agents seen in the stools and the illness.

References

1. Dolin R, Treanor JJ, Madore HP. Novel agents of viral enteritis in humans. J Infect Dis 1987;155:365-76.

2. Ciba Foundation. Novel diarrhoea viruses. Chichester, United Kingdom: Wiley, 1987. (Symposium no. 128).

3. Centers for Disease Control. Outbreak of viral gastroenteritis--Pennsylvania and Delaware. MMWR 1987;36:709-11.

4. Brandt CD, Kim HW, Rodriguez WJ, et al. Pediatric viral gastroenteritis during eight years of study. J Clin Microbiol 1983;18:71-8.

5. Kapikian AZ, Chanock RM. Norwalk group of viruses. In: Fields BN, ed. Virology. New York: Raven Press, 1985:1495-517.

6. Cubitt WD, Blacklow NR, Herrmann JE, Nowak NA, Nakata S, Chiba S. Antigenic relationships between human caliciviruses and Norwalk virus. J Infect Dis 1987;156:806-14.

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