Exposure to tick-borne encephalitis virus among nature management workers in the Netherlands.

Tick-borne encephalitis virus (TBEV) has only recently been detected in the Netherlands. With still few autochthonous tick-borne encephalitis (TBE) patients, human exposure to TBEV is expected to be very low among the general population. We aimed to assess the exposure to TBEV among persons with an occupationally high risk of tick bites in the Netherlands. In our cross-sectional serological survey, employees and volunteers of nature management organizations provided a single blood sample and completed an online questionnaire in 2017. The sera were screened in the anti-TBEV IgG Enzyme-Linked Immunosorbent Assay (ELISA), after which a TBEV-specific virus neutralization test (VNT) was applied to confirm positive ELISA outcomes. Ten sera tested positive for IgG antibodies in the TBEV ELISA, among 556 participants who did not report vaccination against TBEV. Through confirmation in VNT, TBEV-specific IgG antibodies were detected among 0.5% (3/556, 95%CI 0.1%-1.6%). During the five years prior to the questionnaire, 87% reported tick bites. Half of the participants considered that most of their tick bites (75% to 100%) had been acquired while being at work. A very low seroprevalence of TBEV exposure was observed among these nature management workers, even though they report a six times higher exposure to tick bites, compared to our general population. Nonetheless, the emergence of TBEV in the Netherlands reaffirms the need for education and preventative measures against tick bites and tick-borne diseases.

The application of an enzyme-linked immunosorbent assay or an immunofluorescent assay test leads to different estimates of seroprevalence of Coxiella burnetii in the population.

The diagnosis and epidemiological studies of Q fever depend on serology. Among the main methods employed are the enzyme-linked immunosorbent assay (ELISA) and the immunofluorescent assay test (IFAT). We show that two commercial assays representing the two methods with two different cut-off titres can lead to significant differences in diagnostic and seroprevalence estimates. This in turn emphasizes the need for a standardized gold method to compare the various assays; whether this standard is 'in-house' or commercially obtained.

Low seroprevalence of Q fever in The Netherlands prior to a series of large outbreaks.

The Netherlands has experienced large community outbreaks of Q fever since 2007. Sera and questionnaires containing epidemiological data from 5654 individuals were obtained in a nationwide seroprevalence survey used to evaluate the National Immunization Programme in 2006-2007. We tested these sera for IgG phase-2 antibodies against Coxiella burnetii with an ELISA to estimate the seroprevalence and to identify determinants for seropositivity before the Q fever outbreaks occurred. Overall seroprevalence was 1·5% [95% confidence interval (CI) 1·3-1·7]. Corrected for confirmation with immunofluorescence results in a subset, the estimated seroprevalence was 2·4%. Seropositivity ranged from 0·48% (95% CI 0·00-0·96) in the 0-4 years age group to 2·30% (95% CI 1·46-3·15) in the 60-79 years age group. Keeping ruminants, increasing age and being born in Turkey were independent risk factors for seropositivity. The low seroprevalence before the start of the outbreaks supports the hypothesis that The Netherlands has been confronted with a newly emerging Q fever problem since spring 2007.