Isolation of a Coxiella burnetii strain that has low virulence for mice from a patient with acute Q fever

Coxiella burnetii was isolated from a patient with Q fever. It could not be determined whether this was an imported case or an indigenous one. Identification of the isolate was made by electron microscopic morphology and the indirect fluorescent antibody test with convalescent-phase serum from a Q fever patient having a known titer of antibody to C. burnetii. The isolated strain, named TK-1, caused no symptoms in ddY and BALB/c mice except when the mice were treated with cyclophosphamide.