Coxiella, the etiologic agent of Q-fever, are gamma-proteobacteria of the family Legionellaceae. The antibody response to infections by Coxiella burnetii is directed against both lipopolysaccharide and outer-membrane protein antigens, and is most often detected using standard MIF methods. The phase variation in this agent is utilized in serology to differentiate between acute, convalescent and chronic infections.