Proceedings of the 2013 annual meeting of the Netherlands Epidemiology Society
Volume 1 Issue S1 Abstract 23
R.J. Brooke, Julius Center, UMCU, Utrecht, the Netherlands
M.E.E. Kretzschmar, Julius Center, UMC Utrecht; RIVM, Bilthoven, the Netherlands
N.T. Mutters, Heidelberg University Hospital, Heidelberg, Germany
P.F.M. Teunis, RIVM, Bilthoven, the Netherlands; Emory University, Atlanta, USA
The recent outbreak of Q fever in the Netherlands between 2007 and 2009 is the largest recorded outbreak. Exposure to Coxiella burnetii may cause Q fever but the size of the population exposed during the outbreak remained uncertain as little is known of the infectivity of this relatively unknown disease. The quantification of infectious dose and the corresponding response is necessary for assessing the risk to the population.
A human challenge study was published in the 1950s but this study quantified the dose of C. burnetii in relative units. Data from a concurrent guinea pig challenge study were combined with a recent study in which guinea pigs were challenged by the same aerosol route to titrate the inoculum used in the human challenge study to quantify exposure. Concentration estimates for C. burnetii are made jointly with estimates of the dose response parameters in a hierarchical Bayesian framework.
The dose for 50% infection (InfD50%) in human subjects is 1.18 bacteria (95% credible interval (CI) 0.76-40.2). The dose for 50% illness (IllD50) in challenged humans is 5.58 (95%CI 0.89-89.0) bacteria. The probability of a single viable C. burnetii causing infection in humans is 0.44 (95%CI 0.044-0.59) and for illness 0.12 (95%CI 0.0006-0.55).
To our knowledge this is the first human dose-response model for C. burnetii. The estimated dose response relation demonstrates high infectivity in humans. This implies that presence of these bacteria in the environment, even in small numbers, poses a serious health risk to the population.
Published: 06 Jun, 2013