Een legionella -epidemie onder bezoekers van een beurs in Bovenkarspel 1. Beschrijving van de epidemie 2. Patient-controle onderzoek naar de bron
2001
In March 1999 an unexpected high number of patients with atypical
pneumonia was hospitalised in Hoorn. The diagnosis legionellosis was
confirmed by the urine antigen test. An exploratory case control study
suggested that the source should be found at the Westfriesian Flora (WF,
a yearly exhibition organised from February 19 to 28 at Bovenkarspel with
about 80,000 visitors). Subsequently, a national alert was sent out
through the media, a case register was established and the outbreak
investigation was started. This report describes the outbreak using the
data in the case-register, as well as the results of the case-control
study. Separate reports are published on the environmental investigation
and the cohort study.The case-register includes 318 persons among whom
133 confirmed cases and 55 probable cases. The median age was 66 years
(range 20-91 years), the male:female ratio 1.4. The day of onset was
between February 25 and March16; the longest incubation period was 19
days, considerably longer than reported in literature. Except for one
patient with COPD and recurrent pneumonia, all cases -regardless of
earlier visits- visited the Flora on February 23 or later. The
attack-rate per 100,000 visitors according to day of visit increased from
1.1 (February 21) to 53.4 (February 27). The highest number of
hospital admissions was on March 12, the day of the national alert. The
hospitalisation frequency was 86.7%; 19.1% of the patients required
artificial respiration. Twenty-nine persons who were included in the
case-register and had visited the Flora died, among whom 17 confirmed and
four probable cases. The case-fatality rate for confirmed and probable
cases amounted to 0,11.The findings strongly indicate that one or more
sources of infection were contaminated with Legionella spp on or before
February 21; subsequently multiplication of the agent in these sources
led to increasing concentrations of Legionella spp in the exhibition
halls. Three variables were included in the final models of all three
measurements (questionnaire, sketches and floorplan) in the case-control
study: the number of hours visiting the WF (OR 1.6, 2.2 and 1.8
respectively), smoking (OR 3.8, 6.0 and 10.9 respectively) and the
number of hours visiting the consumer products fair with equal duration
of the total visit (OR 0.7, 0.5 and 0.5 respectively). Age was
included in the final model of questionnaire data (OR 1.1) and of
floorplan data (OR 1.2). Halting at the whirlpool in hall 3 was an
explanatory variable in the model of the sketch data (OR 2.6) as well as
the floorplan data (OR 5.8). The variable 'whirlpool' was also
associated with legionellosis in the analysis of questionnaire data.
However, no distinction was made between the two whirlpools and the two
bubblemats.Both from these results and from the results of the
environmental investigation and the cohort study, it was concluded with
reasonable certainty that the whirlpool in hall 3 was the source of the
outbreak.
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