The use of a geographic information system to identify a dairy goat farm as the most likely source of an urban Q-fever outbreak.
BACKGROUND
A Q-fever outbreak occurred in an urban area in the south of the Netherlands in May 2008. The distribution and timing of cases suggested a common source. We studied the spatial relationship between the residence locations of human cases and nearby small ruminant farms, of which one dairy goat farm had experienced abortions due to Q-fever since mid April 2008. A generic geographic information system (GIS) was used to develop a method for source detection in the still evolving major epidemic of Q-fever in the Netherlands.


METHODS
All notified Q-fever cases in the area were interviewed. Postal codes of cases and of small ruminant farms (size >40 animals) located within 5 kilometres of the cluster area were geo-referenced as point locations in a GIS-model. For each farm, attack rates and relative risks were calculated for 5 concentric zones adding 1 kilometre at a time, using the 5-10 kilometres zone as reference. These data were linked to the results of veterinary investigations.


RESULTS
Persons living within 2 kilometres of an affected dairy goat farm (>400 animals) had a much higher risk for Q-fever than those living more than 5 kilometres away (Relative risk 31.1 [95% CI 16.4-59.1]).


CONCLUSIONS
The study supported the hypothesis that a single dairy goat farm was the source of the human outbreak. GIS-based attack rate analysis is a promising tool for source detection in outbreaks of human Q-fever.
Centre for Infectious Disease Control, National Institute for Public Health and the Environment, A van Leeuwenhoeklaan 9, PO Box 1, 3720 BA Bilthoven, the Netherlands.
Barbara
B
Schimmer
Ronald
R
Ter Schegget
Marjolijn
M
Wegdam
Lothar
L
Züchner
Arnout
A
de Bruin
Peter M
PM
Schneeberger
Thijs
T
Veenstra
Piet
P
Vellema
Wim
W
van der Hoek
D000328:Adult; D000818:Animals; D004196:Disease Outbreaks; D005260:Female; D040362:Geographic Information Systems / Q000706:statistics & numerical data*; D015511:Goat Diseases / Q000382:microbiology / Q000635:transmission*; D006041:Goats / Q000382:microbiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D011778:Q Fever / Q000453:epidemiology* / Q000662:veterinary*; D014505:Urban Population; D015047:Zoonoses / Q000453:epidemiology*