[Q Fever Endocarditis-Associated Immune Complex-Mediated Proliferative Glomerulonephritis: Fourth Case from Türkiye].

Q fever is a zoonosis caused by the intracellular gram-negative bacterium Coxiella burnetii. Infection can be asymptomatic, acute or can cause chronic disease. Chronic disease often presents with infective endocarditis (IE). Diagnosis of IE is difficult because the agent does not grow easily in standard blood cultures and valve vegetations are difficult to detect. Glomerular involvement in patients with Q fever endocarditis is limited to the case reports. In addition, a total of three cases of Q fever endocarditis from Türkiye have been published so far. In this case report, a fourth case of Q fever endocarditis from Türkiye accompanied by immune complex-mediated glomerulonephritis was presented. A 35-year-old male patient with a history of mitral and aortic heart valve replacement was admitted with complaints of fever, night sweats and involuntary weight loss. Cervical lymphadenopathy and hepatosplenomegaly were found during the examination. Laboratory investigations revealed anemia inflammation, acute kidney injury (AKI), hematuria and proteinuria. While no causative agent was detected in blood and urine cultures, no diagnosis could be made as a result of bone marrow and cervical lymph node biopsies.Transesophageal echocardiography was performed for the etiology of fever and revealed 7 mm vegetation on the prosthetic mitral valve. C.burnetii phase 1 IgG tested with indirect immunofluorescent antibody method was reported positive at 1/16384 titer and doxycycline and hydroxychloroquine treatments were initiated. Kidney biopsy for the etiology of AKI revealed focal segmental endocapillary proliferative glomerulonephritis with C3, C1q and IgM immunocomplex deposition. After the addition of methylprednisolone to the treatment, the patient's symptoms improved and creatinine and proteinuria levels decreased dramatically. Although Q fever is endemic in our country, it is detected in fewer numbers than expected. In addition to the difficulties in microbiological and clinical diagnosis, the low awareness of physicians about the disease is one of the important reasons for this situation. When the disease comes to mind, the diagnosis can be easily reached by serological methods. Therefore, Q fever should be investigated in the presence of lymphoproliferative disease-like findings fever of unknown origin and culture-negative endocarditis.