Chronic Q fever is a life threatening condition, and is accompanied by high morbidity and mortality, especially for specific subgroups of patients. Long-term quality of life (QOL) is often impaired in patients that were treated for and survive chronic Q fever. Treatment of chronic Q fever should consist of a combination of doxycycline plus hydroxychloroquine, with doxycycline plus quinolones as a potential alternative. Treatment with either doxycycline or quinolones as monotherapy is not advised. Serum doxycyline concentrations (SDC) can be useful to verify if treatment dosage is adequate or to monitor compliance. Measuring SDC was associated with a lower hazard for complications or chronic Q fever-related mortality. There is a need for controlled studies, since all current available studies are observational and thus subject to confounding by indication. Based on the findings from this thesis, we conclude that there is insufficient evidence for an association between C. burnetii and NHL or a causal relationship between Q fever and NHL. Due to methodological drawbacks, the association cannot be excluded definitively. Additional research is needed to provide definite answers with regard to this potential association and its underlying mechanism. Finally, we conclude that the proportion of newly detected chronic Q fever patients through screening among Dutch donors of tissues and cells is very low, and seroprevalence of C. burnetii antibodies is back to pre-outbreak levels. Therefore, it is questionable if screening of Dutch donors of tissues and cells should be continued.