Coxiella burnetii Seroprevalence and Risk for Humans on Dairy Cattle Farms, the Netherlands, 2010–2011

B. Schimmer1

, N. Schotten1, E. van Engelen, J. L. A. Hautvast, P. M. Schneeberger, and Y. T. H. P. van Duijnhoven

Author affiliations: National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands (B. Schimmer, N. Schotten, Y.T.H.P. van Duynhoven); Animal Health Service, Deventer, the Netherlands (E. van Engelen); Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands (J.L.A. Hautvast); Jeroen Bosch Hospital, ‘s-Hertogenbosch, the Netherlands (P.M. Schneeberger)

Abstract

Q fever, caused by Coxiella burnetii, is a recognized occupational infection in persons who have regular contact with ruminants. We determined C. burnetii seroprevalence in residents living or working on dairy cattle farms with >50 adult cows and identified risk factors for seropositivity. Serum samples from farm residents, including employees, were tested for C. burnetii IgG and IgM; seroprevalence was 72.1% overall and 87.2%, 54.5%, and 44.2% among farmers, spouses, and children, respectively. Risk factors included farm location in southern region, larger herd size, farm employment, birds in stable, contact with pigs, and indirect contact with rats or mice. Protective factors included automatic milking of cows and fully compliant use of gloves during and around calving. We recommend strengthening general biosecurity measures, such as consistent use of personal protective equipment (e.g., boots, clothing, gloves) by farm staff and avoidance of birds and vermin in stables.

Q fever is an occupational zoonosis caused by Coxiella burnetii, a gram-negative bacterium (1). Ruminant farmers, laboratory workers, dairy workers, and veterinarians are at particular risk for infection. Humans usually acquire Q fever by inhalation of C. burnetii aerosolized from contaminated materials originating from infected animals. The primary animal reservoirs responsible for human infections are cattle, sheep, and goats, which can shed C. burnetii in urine, feces, milk, and birth products. Before 2007, the seroprevalence of C. burnetii antibodies within the general population of the Netherlands was 2.4%; keeping ruminants and increasing age were risk factors for seropositivity (2). During 2007–2009, Q fever was a major public health problem in the Netherlands; >4,000 human cases were reported (3). Large-scale interventions primarily targeting small ruminants were used to control the epidemic. In 2008, mandatory vaccination was conducted in a defined cluster area and later nationwide. In 2009–2010, a program was implemented to cull pregnant dairy goats and sheep on farms with C. burnetii–positive animals identified through a national bulk tank milk (BTM) screening (4). Since then, the incidence of acute Q fever cases has diminished substantially (5), but chronic cases still occur (6). No epidemiologic associations between Q fever cases in humans and dairy cattle were identified during this epidemic, nor have any been described in other Q fever outbreaks (7). Nevertheless, recent reports indicate that C. burnetii is widespread in Dutch dairy cattle herds (prevalence 78.6% [ELISA] or 56.6% [PCR] among dairy farm herd samples) (8). In 2008, seroprevalence was 16.0% in lactating cows and 1.0% in young animals (8).

C. burnetii seroprevalence estimates for dairy cattle farm residents in the Netherlands are outdated, and risk factors associated with seropositivity are seldom studied. This lack of data inhibits accurate assessment of the public health risk. To inform control measures and provide advice for persons living/working on a dairy cattle farm (DCF), we conducted a cross-sectional study to investigate the seroprevalence of C. burnetii antibodies in DCF residents/workers and identified participant-based and farm-based risk factors for seropositivity. The study was approved by the Medical Ethics Committee of the University Medical Centre Utrecht (no. 09–189/K).