Research article
The use of a geographic information system to identify a dairy goat farm as the most likely source of an urban Q-fever outbreak
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* Corresponding author: Wim van der Hoek wim.van.der.hoek@rivm.nl
1 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
2 Municipal Health Service 'Brabant Zuidoost', Stadhuisplein 2, 5611 EM Eindhoven, the Netherlands
3 Laboratory for Pathology and Medical Microbiology, De Run 6250, 5504 DL Veldhoven, the Netherlands
4 Region East, Food and Consumer Product Safety Authority, De Stoven 22, Postbus 202, 7200 AE Zutphen, the Netherlands
5 Department of Medical Microbiology and Infection Control, Jeroen Bosch Hospital, Tolbrugstraat 11, PO Box 90153, 5200 ME, 's Hertogenbosch, the Netherlands
6 Department of Small Ruminant Health, Animal Health Service, Arnsbergstraat 7, PO Box 9, 7400 AA Deventer, the Netherlands
BMC Infectious Diseases 2010, 10:69 doi:10.1186/1471-2334-10-69
Published: 16 March 2010Abstract
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.