Customize your JAMA Network experience by selecting one or more topics from the list below.
1 figure omitted
Aseptic meningitis is an inflammation of the tissues covering the brain
and spinal cord and caused by a virus, most frequently an enterovirus.1 In August 2003, the Connecticut Department of Public
Health (CDPH) received a report of three viral meningitis cases among recreational
vehicle (RV) campers staying at a campground in northeastern Connecticut.
CDPH, assisted by CDC, conducted an investigation, which (1) identified a
total of 12 cases of aseptic meningitis and 24 cases of enterovirus-like illness
among 201 campers interviewed, (2) demonstrated how transmission of enterovirus
from persons with mild illness contributed to the aseptic meningitis outbreak,
and (3) determined that crowded conditions inside RVs and in the campground
swimming pool likely facilitated spread of enterovirus. Pool operators should
check chlorine and pH levels frequently, particularly during peak pool occupancy;
adults should take precautions against passing enterovirus to children, who
are at greater risk for severe illness.
A retrospective cohort study was conducted of seasonal campers (i.e.,
campers who rented RV sites for the entire summer) via personal interview.
Any person who stayed at least one night at a seasonal campsite during the
study period was considered a cohort member. Response rate was estimated by
using the mean number of campers per campsite to estimate the number at campsites
where campers could not be contacted. A meningitis patient was defined as
a seasonal camper with headache and either neck stiffness or photophobia,
with illness onset during July 16–August 17, 2003. Laboratory-confirmed
cases additionally had ≥10 white blood cells/μL identified by CSF analysis.
Other acute, self-limited illnesses consistent with enteroviral infections
also were identified during the outbreak period. A case of enterovirus-like
illness was defined clinically as an acute illness with any one of the following
symptoms: headache, neck stiffness, photophobia, sore throat, chills, or exanthem
(i.e., acute generalized skin rash) in a seasonal camper with illness onset
during July 16–August 17. Primary campsite illnesses were defined as
the first acute illness of either case type at a campsite. Univariate and
multivariate logistic regression analyses were used to identify predictors
for primary illness. Enterovirus polymerase chain reaction (PCR) and amplicon
sequencing2 were performed at CDC.
Of an estimated 239 seasonal campers, 201 (84%) completed the study
questionnaire. Among the 201 campers, 12 cases of meningitis and 24 other
cases of enterovirus-like illness were identified (attack rates: 6% for meningitis
and 18% for all illness). Four meningitis patients were hospitalized and had
CSF analysis that confirmed aseptic meningitis. At CDC, PCR tests on CSF from
three of these patients detected enterovirus serotype echovirus 9 in two samples.
The CSF sample for the fourth patient was positive for enterovirus by PCR
at a clinical laboratory.
The median age was lower for meningitis patients (14 years; range: 3-42
years) and enterovirus-like illness patients (15 years; range: 3-64 years)
than for well campers (38 years; range: 8 months–80 years). Patients
were more likely to be female among both patient groups (67%) than among well
campers (40%). Illness duration was longer for meningitis patients (median:
7 days; range: 2-28 days) than for enterovirus-like illness patients (median:
3 days; range: 1-21 days). Among the 12 meningitis patients, the most common
symptoms were headache (12), stiff neck (10), nausea (10), and photophobia
(eight). Among the 24 patients with enterovirus-like illness, the most common
symptoms were sore throat (15), headache (12), cough (seven), and diarrhea
Dates of illness onset for meningitis and other enterovirus-like illness
cases were similar and clustered in four peaks, 6-8 days apart (Figure). Two
enterovirus-like illness cases from a single campsite preceded the first illness
peak by 8 days. Four children hospitalized with laboratory-confirmed aseptic
meningitis came from four different campsites. Mothers of three of these children
had an enterovirus-like illness with onset 6-8 days before their child’s
illness onset. The secondary campsite attack rate (29%) was greater than the
primary rate (9%), and attack rates were higher at campsites with more campers
per site: one to two campers per site, 6% (two of 36); three to four campers,
16% (12 of 74); five to six campers, 17% (eight of 47); seven to eight campers,
21% (six of 28); nine to 10 campers, 50% (eight of 16) (age-adjusted trend
analysis; p<0.05). Primary illness was associated with younger age (odds
ratio [OR] for each additional decade of age=0.77; 95% confidence interval=0.59-0.99).
Increasing frequency of submerging one’s head in the campground
pool during the outbreak period was associated with increased risk for primary
illness of either case type (age-adjusted OR=3.3 for one–five times,
5.9 for six–15 times, 6.1 for ≥16 times; p<0.05). Campers reported
that the pool often was crowded at midday (e.g., “wall-to-wall”
swimmers), particularly during weekends. An automated chlorine feeder with
stabilized cyanurated chlorine was in use at the pool throughout the day.
Chlorine levels were checked twice a day (i.e., at approximately 7 a.m. and
8 p.m.) with a handheld test kit. According to written records, chlorine levels
were low (0.5-1.0 mg/L versus the required level of ≥1.5 mg/L) almost every
evening throughout late July and August. The pool operator was not certified
by a national certification group.
At the time of the initial outbreak report, campground staff were advised
to ensure adequate pool chlorination and to clean and disinfect common areas
(e.g., bathrooms, bathhouses, and game room). Through printed bulletins and
informational postings, all campers were directed to (1) wash their hands
frequently, especially after bathroom use, diaper changes, and before eating
or preparing food; (2) avoid sharing eating utensils and drinking containers;
and (3) shower before using the swimming pool. Parents were instructed to
keep children with febrile illness at their campsites until fever and other
D Waite, MD, Day Kimball Hospital, Putnam; P Beckenhaupt, MPH, Northeast
District Dept of Health, Danielson; L LoBianco, MPH, P Mshar, MPH, A Nepaul,
MA, K Marshall, MPH, T Brennan, JL Hadler, MD, Connecticut Dept of Public
Health. WA Nix, M Pallansch, PhD, Div of Viral and Rickettsial Diseases, National
Center for Infectious Dieases; EM Begier, MD, EIS Officer, CDC.
In this aseptic meningitis outbreak, community spread was associated
with swimming in a crowded campground pool. Chlorine levels were low in the
evening; hot sun and high occupancy likely reduced chlorine levels during
the day,3 allowing the pool water to become
intermittently contaminated with enterovirus.
The cohort’s high attack rate was likely facilitated by secondary
intrahousehold enterovirus spread among residents of the same campsite promoted
by crowding; risk for illness was higher in campsites with more campers. Crowding
results in more frequent person-to-person contact and possibly less personal
hygiene (e.g., hand washing). Meningitis illness began in three hospitalized
patients, one incubation period after their mothers’ enterovirus-like
illnesses, suggesting that intrahousehold spread from adults to children was
a source for several more serious infections.
Echovirus 9 was the predominate enterovirus serotype circulating in
the eastern United States during 20034 and
was identified as the likely etiologic agent in this outbreak. Enterovirus
activity typically peaks in temperate climates during the summer and early
fall.5 Based on meningitis data from Connecticut’s
hospital admission syndromic surveillance system, the outbreak occurred in
the weeks preceding widespread community enteroviral transmission in eastern
Connecticut. Enterovirus infections usually are mild illnesses; a small proportion
result in aseptic meningitis.5
The findings in this report are subject to at least two limitations.
First, although the cases of enterovirus-like illness were consistent clinically
with echovirus infection and were linked temporally and epidemically to echovirus
9 aseptic meningitis cases, no laboratory confirmation was attempted. Second,
because the pool was closed for the season by the time interview results were
analyzed, pool water was not tested for enterovirus.
Ongoing contamination of pool water with enterovirus likely facilitated
community transmission. Connecticut’s public health code requires that
water be tested when a pool opens each day and then with sufficient frequency
during bather use to ensure that an adequate disinfection level and pH are
maintained. The free available chlorine residual should be ≥1.5 mg/L for
stabilized cyanurated chlorine, substantially higher than the 0.8 mg/L required
for unstabilized chlorine. Given that an automated chlorine feeder was in
use, the frequent low evening chlorine levels suggest little chlorine was
available earlier in the day during peak bather usage. This outbreak underscores
the importance of testing chlorine and pH during peak pool occupancy, even
if levels are appropriate when a pool is opened.
Swimming has been associated with other enteroviral outbreaks6-8 and other infectious
disease outbreaks.9 To reduce swimming-associated
illness, CDC recommends that (1) staff frequently check pool water chlorine
and pH levels, particularly during periods of heavy bather use, (2) persons
with diarrhea avoid swimming, (3) swimmers shower before pool use and avoid
swallowing pool water, and (4) children be taken to restrooms frequently.3 In addition, CDC recommends improving pool testing,
pool staff training, and public education on appropriate pool use to prevent
recreational water-related illness.10
Children are at greater risk for severe manifestations of enteroviral
infection, including aseptic meningitis1; adults
with enteroviral infection are more likely to experience upper respiratory
or “cold” symptoms only. Hygienic precautions need to be taken
within households as well as among other community members. Enterovirus is
shed in the saliva and feces of infected persons.5 To
minimize viral spread to children in their care, ill caregivers should wash
their hands thoroughly after toilet use and avoid sharing drinks and utensils.
Aseptic Meningitis Outbreak Associated With Echovirus 9 Among Recreational Vehicle Campers—Connecticut, 2003. JAMA. 2004;292(16):1948–1950. doi:10.1001/jama.292.16.1948