A 52-year-old abbatoir employee from northern New South Wales, Australia, injured his right thigh while attempting to stop bovine intestines falling with his foot in November 2011. He had sudden onset of pain in the adductor insertion, radiating down the medial thigh. Over the next week, pain developed in the buttock and lateral thigh to the knee. Pain and swelling continued over the next few months.
Ultrasound 10 days post-injury demonstrated a tear of the adductor magnus, and plain X-ray was normal. Magnetic resonance imaging 2 months later showed extensive marrow oedema in the femoral head and neck, acetabulum and adjacent hemi-pelvis, with partial collapse of the femoral head, oedema of the gluteal and adductor muscles, and a tear in obturator externus. There was hip synovitis and fluid. C-reactive protein was 98.9 mg l-1.
Subsequent X-rays demonstrated a progressive, destructive process in the femur and acetabulum. Bone scan demonstrated avid focal tracer uptake in the right femoral head and neck. Thirteen months post-injury, the Q fever phase I IgG and total antibody titre was >3200 by immunofluorescence (normal <25), consistent with chronic Q fever. At age 40 at pre-immunization screening, the patient's Q fever skin test had been positive, with an induration diameter of 15 mm, while the Q fever IgG enzyme immunoassay index was 1.4 (<1.0) and the phase 2 complement fixation titre was 2.5 (8-32). After that time, he had not taken antibiotics that are active against Q fever.
Seventeen months post-injury, he attended the Infectious Diseases service. The hip was mildly tender, in fixed flexion, with severely limited passive movements, and active movements limited by pain, with non-pitting oedema of the leg. There was quadriceps wasting with no muscle tenderness. He commenced doxycycline and hydroxychloroquine. Histopathology from synovial core biopsy demonstrated non-granulomatous chronic inflammation. Bacterial, fungal, mycobacterial and   C. burnetii   culture and PCR were negative after two doses of doxycycline. Cell culture and PCR were processed at the Australian Rickettsial Reference Laboratory (Geelong, Australia). QuantiFERON-TB Gold and brucellosis serology were negative. Echocardiography was normal.
Pain and mobility were much improved 7 weeks later, at 19 months post-injury. The fixed flexion deformity resolved, with nearly normal range of hip motion. C-reactive protein levels had returned to normal and phase I Q fever antibody titres were much reduced (Fig. 1).
The patient underwent a successful two-stage total hip arthroplasty in February 2014 at 27 months post-injury, taking doxycycline throughout. Standard and   C. burnetii   joint tissue culture and PCR were negative.
The patient received 36 months of doxycycline and hydroxychloroquine, with no relapse in symptoms or radiological change 18 months post-treatment cessation, despite transient elevations in Q fever antibody titres during treatment.