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Community Outbreak of Norwalk Gastroenteritis -- Georgia
An outbreak of gastroenteritis caused by the Norwalk virus
recently occurred in Tate, a rural community in north Georgia. An
investigation implicated the community water system as the source
of
infection.
On January 2-3, 1982, Tate received approximately 4.5 inches of
rainfall. On January 4, residents in homes served by the municipal
water system noted their tap water appeared turbid. That evening,
residents reported the first cases of gastrointestinal illness. A
subsequent investigation by the Office of Epidemiology, Georgia
Department of Human Resources, and the Environmental Protection
Division, Georgia Department of Natural Resources, included
interviews
of affected persons, a community telephone survey, testing of serum
and stool samples from patients, and evaluation of the water
system.
Twenty-seven typically-ill patients identified by local physicians
were interviewed. Illness was generally mild and was characterized
by
abrupt onset of nausea, abdominal cramps, diarrhea and/or vomiting,
headache, myalgias, and low-grade fever. Duration of illness for
most
persons ranged from 1 to 3 days.
Fifty-seven households, systematically selected from a local
directory, were surveyed by telephone. An adult member of each
household provided the following information: age and sex of each
household member and the household's water source, as well as
information on the occurrence of gastrointestinal illness. Cases
of
gastrointestinal illness (defined as vomiting or diarrhea in the
period January 1-9) were reported for 59/193 (30.6%) persons in the
57
households. However, 48/76 (63.2%) persons living in 25 households
served by the municipal water supply were ill, as compared with
11/117
(9.4%) persons living in 32 households served by wells and other
water
sources (p0.001) (Figure 1). Attack rates did not vary among
persons
in different age groups. One or more cases of illness occurred in
20/25 (80.0%) households served by the municipal water supply, as
compared with 5/32 (15.6%) households served by other sources
(p0.001). Based on an estimated 800 persons served by the water
system, approximately 500 people may have been ill during the
outbreak.
Stool cultures obtained from three acutely ill patients were
negative for bacterial pathogens. Paired serum specimens obtained
from 22 patients were tested by radioimmunoassay (RIA) for antibody
to
the Norwalk virus; a greater than or equal to 4-fold rise in
antibody
titer was found for 20 (90.9%) persons. Virus particles were not
detected by electron microscopic examination of the three stool
specimens.
The municipal water system, constructed in 1920, was using
water
from four sources at the time of the outbreak--one well and three
springs. The well casing was below ground level and had been
flooded
during the heavy rains. One of the springs was located inside a
fenced hog lot behind several houses with septic tanks; moreover,
the
spring was unprotected. Testing of a water specimen collected on
January 8 from this spring revealed a fecal coliform count of
16
MPN/100 ml. Tap water from a church, one of five sites sampled on
January 8, had an elevated fecal coliform count (5.1 MPN/100 ml)
and
undetectable residual free chlorine. However, fecal coliforms were
not detected at four sites, where residual free chlorine levels
ranged
from 0.3 to 10.0 mg/L. RIA testing of serum specimens obtained
from
three pigs that had access to the contaminated spring did not
detect
antibody to Norwalk virus.
On January 7, 1982, use of the Tate water sources was
discontinued, and water entering the distribution system was
superchlorinated. Later that day, the system was flushed with
water
from the nearby community, which has since served as Tate's water
source. For a limited time, Tate residents were advised to boil
drinking water. There are no plans to reutilize the Tate water
sources until the observed deficiencies are corrected.
Reported by TC Boswell, MD, DT Darnell, MD, Tate, JL Ledbetter,
Georgia Dept of Natural Resources, J Benson, MD, TW McKinley, MPH,
JD
Smith, BS, RK Sikes, DVM, MPH, State Epidemiologist, Georgia Dept
of
Human Resources; HB Greenberg, MD, NIAID, NIH; Field Svcs Div,
Epidemiology Program Office, CDC. Editorial Note
Editorial Note: The findings of this investigation strongly
implicated the Tate water system as the source for Norwalk virus
infection. Fecal contamination of tap water sampled on Friday,
January 8, was observed at one of five sites tested, a church,
where
weekday water use was infrequent. Although data concerning water
consumption by residents were not obtained, household residents
served
by the Tate system probably became infected after drinking water
contaminated with Norwalk virus. Inspection of the four water
sources
for the system revealed two possible sites of contamination,
including
the spring in which fecal coliforms were detected. That spring was
subject to contamination for several reasons: the cover was
damaged,
and the spring was open to ground-water runoff from nearby homes
with
septic tanks and penned animals and to the excreta of pigs that had
direct access to the spring. In addition, the casing of the single
well was recessed below ground level and had been exposed to
flooding
by surface water during the unusually heavy rainfall. The
possibility
cannot be dismissed that inadequate chlorination of the water
system
contributed to the outbreak.
A variety of etiologic agents have been implicated in
water-related disease outbreaks, including bacterial, viral, and
parasitic pathogens and chemical toxins (1). The clinical and
epidemiologic features of this outbreak were characteristic of
Norwalk
infection and resembled patterns observed in previous waterborne
Norwalk-associated outbreaks involving general population groups
(2-5). This episode illustrates the importance of promptly
reporting
and investigating community outbreaks of gastroenteritis. A prompt
response to this outbreak made possible identification of the
causative agent and implementation of measures designed to prevent
future outbreaks of waterborne illness in this community.
References
CDC. Water-related disease outbreaks surveillance. Annual
summary, 1980. Atlanta:CDC, 1982.
Kaplan JE, Gary GW, Baron RC, et al. Epidemiology of Norwalk
gastroenteritis and the role of Norwalk virus in outbreaks of
acute nonbacterial gastroenteritis. Ann Intern Med
1982;96:756-61.
Gunn RA, Terranova WA, Greenberg HB, et al. Norwalk virus
gastroenteritis aboard a cruise ship: an outbreak on five
consecutive cruises. Am J Epidemiol 1980:112:820-7.
Griffin MR, Surowiec JJ, McCloskey DI, et al. Foodborne
Norwalk
virus. Am J Epidemiol 1982;115:178-84.
Baron RC, Murphy FD, Greenberg HB, et al. Norwalk
gastrointestinal illness: an outbreak associated with swimming
in
a recreational lake and secondary person-to-person
transmission.
Am J Epidemiol 1982;115:163-72.
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