Sixteen cases of chronic Q fever are described. In eight there was a history of exposure to infection from farms or farm products. All had valvular heart disease, involving the mitral valve in nine and the aortic valve in seven. Infection occurred on a prosthetic valve in two patients. Arterial embolism was common. Venous thrombosis occurred in three patients, and pulmonary embolism occurred in three other patients.Complement fixing antibodies to phase 1 antigen were found in a titre of 1:200 or greater in all except two patients. In one of these post-mortem examination revealed rickettsial bodies in mitral valve vegetations, and in the otherCoxiella burnetiwas isolated from heart valve tissue.The majority presented with infective endocarditis but two presented primarily with liver disease. All patients had evidence of liver involvement and in one this led to death from cirrhosis. Abnormal tests of liver function, particularly hyperglobulinaemia, raised alkaline phosphatase and abnormal bromsulphthalein retention were found in all patients. Hepatic histology was abnormal in all eight patients in whom it was studied. The commonest features were mononuclear cell infiltration of the portal tracts and prominence of the sinusoidal Kupffer cells. Patchy focal necrosis of parenchymal cells, granulomata, fatty change, and eosinophilia of the sinusoidal walls were also noted in several patients and cirrhosis developed in one.Six patients had a purpuric rash, and in 12 there was thrombocytopenia. It is suggested that the presence of hepatomegaly and liver involvement and thrombocytopenia may help to differentiate Q fever endocarditis from bacterial endocarditis.Raised serum IgM and IgA levels occurred frequently, but with only a moderate dominance of IgM. Sheep cell agglutination and latex fixation tests for rheumatoid factor were occasionally positive. Several features of the disease suggest the possibility that immune-complex mechanisms may play a role in chronic Q fever.Treatment was with prolonged courses of tetracycline usually combined with lincomycin. Seven patients underwent valve replacement surgery for haemodynamic reasons. Five patients died; two from heart failure, one from cirrhosis, one seven days after valve replacement and one from intraperitoneal haemorrhage following percutaneous liver biopsy.Three patients have survived for more than five years, and another six for more than three and a half years after diagnosis. Of these nine patients, three received medical therapy alone and six required valve replacement as well. Antibiotics have been discontinued in four patients who have had valve surgery and three others. Six patients had received antibiotics for continuous periods varying from 29–62 months. In the period after stopping therapy varying from 15–21 months, no relapse has occurred. A seventh patient, who had received antibiotics for four months prior to valve replacement, has survived 43 months after the withdrawal of antibiotics.It is suggested that antibiotic therapy with tetracycline and lincomycin may control the disease, and that valve surgery may not be necessary to achieve this. In view of the known propensity for this organism to persist in a quiescent form for long periods even without treatment, we recommend careful monitoring of these patients after treatment is withdr
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