Abstract
BackgroundFrom 2007 to 2010, (the southern part of) the Netherlands experienced a large Q fever epidemic, with more than 4,000 reported symptomatic cases. Approximately 1 - 5% of the acute Q fever patients develop chronic Q fever. A high IgG antibody titre against phase I of Coxiella burnetii during follow-up is considered a marker of chronic Q fever. However, there is uncertainty about the significance and cause of persistence of high IgG phase I antibody titres in patients that do not have any additional manifestations of chronic Q fever. We studied whether continued or repeated exposure to the source of infection could explain elevated IgG phase I antibody levels.MethodsA case-control study was performed to analyze predictors for possible chronic Q fever. Possible chronic Q fever cases (n = 53) are patients with phase I IgG antibody titre ≥1:1,024 at any point in the 9 - 18 months after acute Q fever diagnosis, with a negative PCR test result for C. burnetii DNA and without other disease manifestations. Controls (n = 110) are acute Q fever patients that did not develop chronic Q fever, and who consistently had phase I IgG antibody titre <1:1,024 during the 9 - 18 months follow-up. Binary logistic regression was performed to analyze the effect of living close to an infected farm on the high antibody titres. A longitudinal analysis described the serological profiles of cases and controls.ResultsProximity to infected farms and contact with animal placental material were not associated with an increased risk for possible chronic Q fever. Possible chronic Q fever patients have high IgG phase II as well as IgG phase I antibody titres, even after 48 months of follow-up.ConclusionWe were unable to explain the cause of persistent high IgG phase I titres among possible chronic Q fever patients by being continuously exposed to the source of infection.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-014-0629-6) contains supplementary material, which is available to authorized users.
Highlights
From 2007 to 2010, the Netherlands experienced a large Q fever epidemic, with more than 4,000 reported symptomatic cases
Study design A case–control study was performed to evaluate whether continued exposure to the source of infection is associated with persistent high phase I IgG antibody titres among possible chronic Q fever patients, and to study the effect of living close to an infected farm on the high levels of IgG phase I and phase II antibody titres
Population data Study population The study population consisted of Q fever patients, that were recruited from the Jeroen Bosch Hospital (JBH) in ’s-Hertogenbosch, Bernhoven Hospital (BH) in Uden, and from the Laboratory for Pathology and Medical Microbiology (PAMM) in Veldhoven
Summary
From 2007 to 2010, (the southern part of) the Netherlands experienced a large Q fever epidemic, with more than 4,000 reported symptomatic cases. A high IgG antibody titre against phase I of Coxiella burnetii during follow-up is considered a marker of chronic Q fever. There is uncertainty about the significance and cause of persistence of high IgG phase I antibody titres in patients that do not have any additional manifestations of chronic Q fever. We studied whether continued or repeated exposure to the source of infection could explain elevated IgG phase I antibody levels. Pregnancy, and immunosuppression are at higher risk for developing chronic Q fever [3,4,8]. Being present when animals give birth increases the risk of infection, since high concentrations of bacteria are found in placental material [11,20]. Environmental conditions in the surrounding of an infected farm might play a role in the spread of the infection: dry soil conditions with little vegetation and high particulate matter concentrations in the air are possible risk factors [24,25,26]
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