Coxiella burnetii is the agent of Q fever, or "query fever," a zoonosis first described in Australia in 1937. Since this first description, knowledge about this pathogen and its associated infections has increased dramatically. We review here all the progress made over the last 20 years on this topic. C. burnetii is classically a strict intracellular, Gram-negative bacterium. However, a major step in the characterization of this pathogen was achieved by the establishment of its axenic culture. C. burnetii infects a wide range of animals, from arthropods to humans. The genetic determinants of virulence are now better known, thanks to the achievement of determining the genome sequences of several strains of this species and comparative genomic analyses. Q fever can be found worldwide, but the epidemiological features of this disease vary according to the geographic area considered, including situations where it is endemic or hyperendemic, and the occurrence of large epidemic outbreaks. In recent years, a major breakthrough in the understanding of the natural history of human infection with C. burnetii was the breaking of the old dichotomy between "acute" and "chronic" Q fever. The clinical presentation of C. burnetii infection depends on both the virulence of the infecting C. burnetii strain and specific risks factors in the infected patient. Moreover, no persistent infection can exist without a focus of infection. This paradigm change should allow better diagnosis and management of primary infection and long-term complications in patients with C. burnetii infection.

Introduction: COVID-19 presents benign forms in young patients who frequently present with anosmia. Infants are rarely infected, while severe forms occur in patients over 65 years of age with comorbidities, including hypertension and diabetes. Lymphopenia, eosinopenia, thrombopenia, increased lactate dehydrogenase, troponin, C-reactive protein, D-dimers and low zinc levels are associated with severity.Areas covered: The authors review the literature and provide an overview of the current state of knowledge regarding the natural history of and therapeutic options for COVID-19. Expert opinion: Diagnosis should rely on PCR and not on clinical presumption. Because of discrepancies between clinical symptoms, oxygen saturation or radiological signs on CT scans, pulse oximetry, and radiological investigation should be systematic. The disease evolves in successive phases: an acute virological phase, and, in some patients, a cytokine storm phase; an uncontrolled coagulopathy; and an acute respiratory distress syndrome. Therapeutic options include antivirals, oxygen therapy, immunomodulators, anticoagulants and prolonged mechanical treatment. Early diagnosis, care, and implementation of an antiviral treatment; the use of immunomodulators at a later stage; and the quality of intensive care are critical regarding mortality rates. The higher mortality observed in Western countries remains unexplained. Pulmonary fibrosis may occur in some patients. Its future is unpredictable.