Abstract
An analysis of 3,264 notifications for acute Q fever show that the patients were mostly men, smokers and persons aged 40–60 years. Pneumonia was the most common clinical presentation in >60% of patients. Fewer than 5% of the notified patients were working in the agriculture sector or meat-processing industry, including
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abattoirs. The outbreaks in the Netherlands can therefore not be explained by occupational exposure. To estimate the number of infections, including those that remain asymptomatic, notification rates were compared with seroconversion rates in blood donors from whom serial samples were available. This resulted in a ratio of one Q fever notification to 12.6 incident infections of Coxiella burnetii. Control measures during the epidemic in the Netherlands primarily focused on dairy goat farms. However, in many other countries, outbreaks have been associated with non-dairy sheep and the Netherlands has many more sheep than goats. 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 but not around infected meat sheep farms. An analysis of datasets on vegetation, land use, soil characteristics, and weather conditions in 5 km areas around infected farms suggest that intensive goat and sheep husbandry should be avoided in areas that are characterized by a combination of arable land with deep groundwater and little vegetation. Awareness of Q fever among patients and doctors can influence health seeking behaviour, laboratory testing practices, and the number of notifications. However, analysis of unbiased serological data from pregnant women in the high incidence area confirmed that presence of antibodies against C. burnetii is related to proximity to infected dairy goat farms. In a retrospective analysis the presence of antibodies against C. burnetii was not significantly associated with preterm delivery, low birth weight, or several other adverse outcome measures. This is in contrast to previous reports from the international literature. In a follow-up study of 686 patients with acute Q fever, 11 cases of chronic Q fever were identified based on serological profile, PCR results, and clinical presentation. In a comparison of various serological algorithms, IgG phase I titre ≥1:1,024 at 6 months had the most favourable sensitivity and positive predictive value for the detection of chronic Q fever. However, the diagnosis of chronic Q fever must be based primarily on clinical grounds. In the aftermath of the epidemic, with a seroprevalence >12% in the most affected area in the south of the country, questions remain about the follow-up of acute Q fever patients, screening of groups at risk for chronic Q fever, screening of donors of blood and tissue, and human vaccination.
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