|
I.A. van
Asperen 1, T. Mank 2, G.J. Medema 1,
C. Stijnen 3, A.S. de Boer 1, J.F. Groot 4,
P. Ten Ham 5, J.F. Sluiters 6, M.W. Borgdorff 1
1 National Institute of Public
Health and the Environment, The Netherlands
2
General Practitioners Laboratory, Haarlem, The Netherlands
3 Ruwaard van Putten Hospital,
Spijkenisse, The Netherlands
4
Regional Health Department, Spijkenisse, The Netherlands
5 Regional Health Department,
Haarlem, The Netherlands
6
University Hospital, Rotterdam, The Netherlands
The outbreak
A hospital microbiologist in Spijkenisse, in the
south west of the Netherlands - who had recently attended a parasitology
course - identified cryptosporidial oocysts in stools from a patient with
diarrhoea on 16 August 1995. Re-examination of 89 stool specimens received
since 10 August in which no bacterial pathogen had been identified revealed
15 cases of cryptosporidiosis, which were confirmed at the parasitology
laboratory of the University of Leiden (Dr A.M. Polderman). Most cases
were children aged £5
years and women aged 25-35 years, none of whom had evidence of impaired
immunity.
Only parasitology departments in the Netherlands
routinely examine stools for cryptosporidial oocysts and baseline data
on the prevalence of cryptosporidiosis are sparse. Two surveys of patients
with gastroenteritis suggest that 1% to 2% have cryptosporidiosis, with
a peak of 3% to 4% in June and August (1, and personal communication L.M.
Kortbeek, National Institute), much smaller proportions than the 17% in
Spijkenisse in August 1995. On 31 August, the Dutch Medical Inspectorate
commissioned the National Institute to investigate the source of the outbreak.
Investigation of the water supply
The public water supply of Spijkenisse was a potential
source of the outbreak so the water supply was sampled and analysed (2)
at two sites on 29 August (1500 litres at each site). Data on the water
treatment processes and maintenance or repair procedures in the water
distribution system were investigated for any disruptions/failures. A
3 mm filter of the
demineralised water installation of the Spijkenisse hospital laboratory,
which had been in place since June 1995, was also examined for
cryptosporidial oocysts on 11 September. Data from the treatment plant
provided no evidence of treatment failures or contamination after treatment,
and samples from tap water and the filter were negative for cryptosporidium.
No preventive or corrective measures were taken either at the treatment
plant or to the consumer supply. The public was informed that the public
water supply was safe.
Cryptosporidiosis incidence study
A study of the incidence of cryptosporidiosis was
carried out in five laboratories in the south west and north west parts
of the country. Cryptosporidial oocysts were detected in 147 of 1495 successive
stool specimens from patients with gastroenteritis examined in September
and October 1995 (10%, range 5-14%). The incidence declined by the end
of September. The survey showed that the proportion of stool specimens
from patients with gastroenteritis in which cryptosporidial oocysts were
found had risen in all five regions of the country. The areas investigated
received their water from different public water supplies.
Case control study
A case control study was carried out in the catchment
areas of the Spijkenisse and Haarlem laboratories. Data from laboratory
surveillance was used to find cases. A case of cryptosporidiosis was defined
as a person who became ill with diarrhoea after 15 July 1995 and in whose
stools cryptosporidial oocysts were detected between 4 and 26 September.
Positive results were confirmed at the parasitology departments of the
National Institute and the University Hospital of Rotterdam. Ten controls
of the same sex and year of birth as each case were selected at random
from local populations. It was planned that two controls, selected at
random from the ten identified, should be interviewed for each case but
in four cases only one control could be interviewed. Interviews were carried
out by telephone using a standardised questionnaire, to obtain age, sex,
details of illness including onset and duration, predisposing diseases,
and exposure to recognised risk factors in the two to four weeks before
the onset of diarrhoea. Information from matched controls was collected
for the same calendar period as for the cases. Seventy-one cases, aged
0-65 years (median 5 years) included in the study were matched to 138
controls. All cases reported diarrhoea, 51 reported stomach cramps and
weight loss. A common source for the outbreak was not identified. Using
conditional logistic regression, household contact with people with diarrhoea
and swimming in municipal pools (no particular pool implicated) were significantly
associated with illness (odds ratios (OR) 5.4; 95% confidence interval
(CI) 2.0-14.7 and OR 3.9; 95% CI 1.5-10.2, respectively). An apparent
association with visiting day care centres in Haarlem did not reach statistical
significance (OR 2.01; 95% CI 0.01-9.9). The median duration of illness
was 25 days, 40% of cases rested in bed for a median of seven days, and
half of the cases reported having taken a median of four days off work
or school.
Discussion
This is the first outbreak of cryptosporidiosis detected
in the Netherlands. As routine investigation of faecal specimens in the
Netherlands does not include cryptosporidium, previous increases in the
incidence of cryptosporidiosis may not have been recognised. Loose stool
specimens have been examined specifically for cryptosporidium in the Haarlem
laboratory since January 1993, and an increased incidence has been observed
in the Haarlem area every summer. The peak in 1995, however, was higher
than in previous years. Our incidence study suggests that cryptosporidiosis
may have a seasonal distribution nationwide. Bathing in swimming pools
or surface waters may contribute to the observed seasonal distribution.
Cryptosporidial oocysts are highly resistant to most common chemical disinfectants,
including chlorine, and may persist in pool water for some time, if the
pool is not well maintained, increasing the risk of transmission. Several
outbreaks have been linked to swimming pools (3,4). Surface waters have
been identified previously as a cause of cryptosporidiosis (5). Transmission
of cryptosporidiosis through pool or surface water is facilitated by the
low infective dose of cryptosporidium (6). We investigated two fresh water
lakes and sea water in both areas and found cryptosporidial oocysts in
some samples, but the case control study showed no increased risk associated
with bathing in surface waters.
We recommend strengthening cryptosporidium surveillance
through the routine examination of stools of patients with gastroenteritis
in selected laboratories, to investigate seasonality in cryptosporidiosis
and to facilitate prompt recognition of widespread outbreaks. Further
studies on the role of swimming pools and surface waters in the transmission
of cryptosporidiosis are needed (7).
References
1. Bänffer JRJ, Duifhuis JCC. Cryptosporidiose:
prevalentie in de regio Rotterdam en vergelijking van twee kleuringstechnieken.
Ned Tijdschr Geneeskd 1989: 133; 2229-33.
2. Le Chavallier, MW, Norton WD, Siegel JE,
Abbaszadegan M. Evaluation of the immunofluorescence procedure for detection
of Giardia cysts and Cryptosporidium oocysts in water. Appl Environ
Microbiol 1995; 61: 690-7.
3. McAnully JM, Fleming DW, Gonzalez AH. A
community-wide outbreak of cryptosporidiosis associated with swimming
at a wave pool. JAMA 1994; 272: 1597-1600.
4.Sorvillo FJ, Fujioka K, Nahlen B, Tormey
MP, Kebabjian R, Mascola L. Swimming-associated cryptosporidiosis. Am
J Publ Health 1992; 82: 742-4.
5. Gallaher MM, Herndon JL, Nims LJ, Sterling
CR, Grabowski DJ, Hull HF. Cryptosporidiosis and water. Am J Publ Health
1989; 79: 39-42.
6. DuPont HL, Chappell CL, Sterling CR, Okhuysen
PC, Rose JB, Jakubowski W. The infectivity of Cryptosporidium parvum in
healthy volunteers. N Engl J Med 1995; 332: 855-9.
7. Cryptosporidium in water supplies. UK Departments
of Environment and Health. Report of a Group of Experts. Chaired by Sir
John Badenoch. London: HMSO, 1990.
|