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- Title
Q Fever: Single-Point Source Outbreak With High Attack Rates and Massive Numbers of Undetected Infections Across an Entire Region.
- Authors
Hackert, Volker H.; van der Hoek, Wim; Dukers-Muijrers, Nicole; de Bruin, Arnout; Al Dahouk, Sascha; Neubauer, Heinrich; Bruggeman, Cathrien A.; Hoebe, Christian J. P. A.
- Abstract
We present an essential prospective case study linking a veterinary outbreak of Q fever on a single dairy-goat farm to a human Q-fever cluster with massive numbers of undetected infections and exceedingly high attack rates across an entire region.Background. In early 2009, a dairy-goat annex care farm in South Limburg, the Netherlands, reported 220 Coxiella burnetii–related abortions in 450 pregnant goats. These preceded human cases and occurred in a region that was Q-fever free before 2009, providing a unique quasi-experimental setting for investigating regional transmission patterns associated with a Q-fever point source.Methods. Index-farm residents/employees, visitors, and their household contacts were traced and screened for C. burnetii. Distribution of community cases was analysed using a geographic information system. True incidence, including undetected infections, was estimated regionwide by seroprevalence in a pre- versus postoutbreak sample, and near-farm by immunoglobulin M seroprevalence in a municipal population sample. Environmental bacterial load was repeatedly measured in surface and aerosol samples.Results. Serological attack rate was 92% (24/26) in index-farm residents/employees, 56% (28/50) in visitors, and 50% (7/14) in household contacts, and the clinical attack rate (ie, the proportion of persons seropositive for acute infection who also had clinical illness) was ≥80%. Notified symptomatic community cases (n = 253) were scattered downwind from the index farm, following a significant exposure-response gradient. Observed incidence ranged from 6.3% (0–1 km) to 0.1% (4–5 km), and remained high beyond. True incidence of infections was estimated at 2.9% regionwide, extrapolating to 8941 infections; estimated near-farm incidence was 12%. Coxiella burnetii load was high on-farm (2009), and lower off-farm (2009–2010).Conclusions. Linking a single dairy-goat farm to a human Q-fever cluster, we show widespread transmission, massive numbers of undetected infections, and high attack rates on- and off-farm, even beyond a 5-km high-risk zone. Our investigation may serve as an essential case study for risk assessment in public health and related fields such as bioterrorism response and preparedness.
- Subjects
Q fever; DISEASE outbreaks; DAIRY farms; BIOTERRORISM; PUBLIC health; CASE studies
- Publication
Clinical Infectious Diseases, 2012, Vol 55, Issue 12, p1591
- ISSN
1058-4838
- Publication type
Article
- DOI
10.1093/cid/cis734