Q Fever among Culling Workers, the Netherlands, 2009–2010

In 2009, dairy goat farms in the Netherlands were implicated in >2,300 cases of Q fever; in response, 51,820 small ruminants were culled. Among 517 culling workers, despite use of personal protective equipment, 17.5% seroconverted for antibodies to Coxiella burnetii. Vaccination of culling workers could be considered.

or IgG positive. Positive results were confi rmed by immunofl uorescence assay (Focus Diagnostics, Cypress, CA, USA) titers >32. Symptomatic infection was defi ned as fever or rigors and >1 of the following after December 1, 2009: malaise, headache, cough, nausea, diarrhea, shortness of breath, pleuritic chest pain, or myalgia. Intensity of occupational exposure was summarized as follows: hours worked, weighted mean farm size (animal number), whether animal abortions were reported, and whether work was performed on average inside or outside the stable (proxy for direct/indirect animal contact). Months worked were dichotomized as cold (December 2009-March 2010) (5) and warm (April-June 2010) (6). Use of PPE was classifi ed as compliant or noncompliant.
To calculate distance of workers' residence to the nearest infected farm, we used ArcGIS software (www.esri.com/software/arcgis/index.html). We used Stata version 11 (StataCorp LP, College Station, TX, USA) to examine univariable associations (Pearson χ 2 or Fisher exact test). Variables with probability p<0.2 and known risk factors for Q fever were selected for binomial regression analyses. Interactions between signifi cant variables in the multivariable model were investigated. Missing values were excluded.
Of 517 participants, 453 gave pre-cull blood samples, 246 of these gave post-cull samples, and 351 completed the questionnaire. Age, gender, and residential distance from the nearest infected farm were available from occupational records. Participant median age was 47 years (range 19-67 years); 97% were male. Before culling, 14 (3.1%) were IgM II and IgG II positive, 8 (1.8%) were IgM II positive only, 36 (8%) were IgG II positive only, and 395 (87%) were IgG II and IgM II negative; i.e., any seropositivity was found for 13.0%. Pre-cull blood samples indicated more seropositivity among workers who lived within 5 km of an infected farm and had regular work contact with sheep and goats (excluding culling). Prior culling experience was more common among seronegative than seropositive workers (Table 1). Among those who were IgG seropositive before culling, none became IgM seropositive after culling.

Conclusions
Seroconversion for C. burnetii among 17.5% of culling workers who were seronegative before culling provides evidence of high-risk work. Before culling, seroprevalence was 13%, similar to that among blood donors in a highincidence area in the Netherlands in 2009 (H.L. Zaaijer, pers. comm.) and in similar high-risk occupational groups (7). Laboratory testing by using ELISA is an accepted method in an acute setting (8), and positive results (including positive IgM only) were confi rmed by immunofl uorescence assay. Nonparticipants were in the youngest and oldest age groups; their effect on the proportion of seroconversion is uncertain. Eighteen workers (excluded for not providing a follow-up blood sample) completed the questionnaire in June. Symptom incidence for these 18 workers was the same as that for included participants.
Symptomatic infection (31% of seroconverters) was probably underestimated. A diagnosis of Q fever was selfreported (unconfi rmed) to the occupational health service by 8 workers who did not participate in the study. During December-July 2010, the national infectious disease surveillance system reported 11 culling-related cases of acute Q fever; 2 of these patients were hospitalized.
A strong association was shown between risk for seroconversion and total hours worked on the farms and working inside the stable. In other settings internationally, a risk gradient has also been shown for close direct and indirect animal contact over time (9,10). In our study, half the participants had experience with previous animal epidemics (avian infl uenza, foot-and-mouth disease, classical swine fever) and using PPE. Their compliance with PPE was reportedly high; however, a key problem was not wearing PPE while taking work breaks but remaining on the farm.
Given the high risk for infection despite extensive personal protective measures during culling, additional preventive measures are needed. The Health Council of the Netherlands issued guidelines for persons in risk groups who would benefi t from vaccination against Q fever (11). Culling workers were not included in these guidelines. The effi cacy of human Q fever vaccine has been shown to be high for young and healthy persons in similar occupational groups (12)(13)(14). Vaccination of culling workers could be considered if further animal culling is advised. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 17, No. 9, September 2011