Smooth incidence maps give valuable insight into Q fever outbreaks in The Netherlands

Abstract

Abstract. From 2007 through 2009, TheNetherlands faced large outbreaks of human Q fever. Control measures focused primarily on dairy goat farms because these were implicated as the main source of infection for the surrounding population. However, in other countries, outbreaks have mainly been associated with non-dairy sheep and The Netherlands has many more sheep than goats. Therefore, a public discussion arose about the possible role of non-dairy (meat) sheep in the outbreaks. To inform decision makers about the relative importance of different infection sources, we developed accurate and high-resolution incidence maps for detection of Q fever hot spots. In the high incidence area in the south of the country, full postal codes of notified Q fever patients with onset of illness in 2009, were georeferenced. Q fever cases (n = 1,740) were treated as a spatial point process. A 500 x 500 m grid was imposed over the area of interest. The number of cases and the population number were counted in each cell. The number of cases was modelled as an inhomogeneous Poisson process where the underlying incidence was estimated by 2-dimensional P-spline smoothing. Modelling of numbers of Q fever cases based on residential addresses and population size produced smooth incidence maps that clearly showed Q fever hotspots around infected dairy goat farms. No such increased incidence was noted around infected meat sheep farms. We conclude that smooth incidence maps of human notifications give valuable information about the Q fever epidemic and are a promising method to provide decision support for the control of other infectious diseases with an environmental source.

Coxiella burnetii infections in sheep or goats: an opinionated review

“…Subsequently, it was demonstrated that, during the outbreaks in the Netherlands, infected sheep were a source of infection to humans only in case of direct contact with the sheep, but not for the surrounding population (van der Hoek et al, 2012b).…”

Detection of Coxiella burnetii in Aborted Fetuses of Cattle and Sheep Using Polymerase Chain Reaction Assay in Mashhad City, Iran

“…Epidemiological researches have reported that abortion waves on dairy goat flocks could be a source for human infection especially people living near to the flocks (31). Humans are infected through inhalation of aerosols generated from contaminated placentas and body fluids (3).…”

Spatial methods for infectious disease outbreak investigations: systematic literature review

“…Although the simple dot map was the most commonly used method, a wide range of techniques were applied, including more sophisticated data visualisations and analytic tools. Across the range of studies, there were examples of spatial tools being usefully applied throughout the course of an outbreak investigation; from initial confirmation of the outbreak to describing and analysing [11,18-28,30-36,38,40-50,55,56,58-60, 63,67-69,71-76,80,82-85,87-93,96-105] Thematic map 25 [18,19,[21][22][23]28,29,38,41,42,45,46,50,60,68,70,74,80,82,89,91,[93][94][95]103] Rate map 14 [20,30,44,45,49,50,57,63,70,76,79,81,90,101] Smoothed incidence map 13 [11,31,[48][49][50]73,…”

“…Several studies also highlighted the usefulness of maps in reports or Reports by continent presentations to communicate results to health officials [29,47], policymakers [49,50] and the public [38]. Sarkar and colleagues, for example, presented dot maps of cases of acute diarrhoeal disease in a village in southern India to the local community and health authorities [46].…”