A nested case control study demonstrating increased chronic fatigue six years after a Q fever outbreak

Abstract

The frequency and range of long-term sequelae following acute Q fever infection remains controversial. This study aimed to assess a range of potential psychological and physical sequelae in a follow up study of a large outbreak of Q fever that occurred in Newport, Wales, in 2002. A nested case control study was undertaken six years after a point source outbreak of Q fever. We invited a cohort of 211 factory workers exposed to a point source of Q fever in 2002 to attend a follow up clinic in 2008. Cases, defined as those who had clinical symptoms and serological evidence of acute Q fever in 2002, were compared to controls, who worked in the same factory but were serologically negative at the time of the outbreak. At the follow up clinic blood was taken for Coxiella burnetii microimmunofluorescence and questionnaires were completed including the PHQ-9, Chalder Fatigue scale, and General Health Questionnaire. Results were obtained for 32 cases and 13 controls. Chalder Fatigue scores were significantly raised in the cases (independent samples t-test: P=0.047). PHQ-9 and GHQ scores were not significantly raised in cases. However, post hoc cross sectional analysis indicated a relationship between Phase 2 IgG at follow up in 2008 and Chalder Fatigue scores (P=0.004) and PHQ-9 scores (0.049). A longitudinal association was demonstrated between acute Q fever infection and chronic fatigue six years later. In crosssectional analysis a previously unreported relationship between depression scores (PHQ- 9) and positive Q fever serology was also identified.

Keywords

• Q fever, Coxiella burnettii, chronic fatigue syndrome, chalder fatigue scale, PHQ-9