title: Smooth incidence maps give valuable insight into Q fever outbreaks in The Netherlands.
abstract: From 2007 through 2009, The Netherlands 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.
authors.affiliation: Centre for Infectious Disease Control, National Institute for Public Health and the Environment, PO Box 1, 3720 BA Bilthoven, The Netherlands. wim.van.der.hoek@rivm.nl
authors.forename: Wim
authors.initials: W
authors.lastname: van der Hoek
authors.forename: Jan
authors.initials: J
authors.lastname: van de Kassteele
authors.forename: Ben
authors.initials: B
authors.lastname: Bom
authors.forename: Arnout
authors.initials: A
authors.lastname: de Bruin
authors.forename: Frederika
authors.initials: F
authors.lastname: Dijkstra
authors.forename: Barbara
authors.initials: B
authors.lastname: Schimmer
authors.forename: Piet
authors.initials: P
authors.lastname: Vellema
authors.forename: Ronald
authors.initials: R
authors.lastname: ter Schegget
authors.forename: Peter M
authors.initials: PM
authors.lastname: Schneeberger
mesh_terms: D000034:Abortion, Veterinary / Q000453:epidemiology / Q000209:etiology / Q000382:microbiology; D000383:Agriculture / Q000706:statistics & numerical data; D000818:Animals; D016000:Cluster Analysis; D016997:Coxiella burnetii / Q000472:pathogenicity; D003612:Dairying / Q000706:statistics & numerical data*; D004196:Disease Outbreaks / Q000706:statistics & numerical data / Q000662:veterinary*; D004781:Environmental Exposure / Q000009:adverse effects / Q000706:statistics & numerical data; D005260:Female; D062305:Geographic Mapping; D006041:Goats / Q000382:microbiology; D006801:Humans; D015994:Incidence; D009426:Netherlands / Q000453:epidemiology; D016012:Poisson Distribution; D011247:Pregnancy; D016016:Proportional Hazards Models; D011778:Q Fever / Q000453:epidemiology* / Q000635:transmission / Q000662:veterinary; D012756:Sheep / Q000382:microbiology; D015047:Zoonoses / Q000453:epidemiology* / Q000209:etiology / Q000382:microbiology