# Case Report: A rare case of ANCA-positive Q fever endocarditis-associated glomerulonephritis

## TL;DR

A 12-year-old boy with a heart condition was diagnosed with a rare case of Q fever endocarditis that caused kidney inflammation and positive ANCA antibodies.

## Contribution

This is a rare pediatric case report of Q fever endocarditis-associated glomerulonephritis with ANCA positivity.

## Key findings

- Q fever endocarditis was diagnosed in a child with Tetralogy of Fallot using mNGS and IFA.
- The patient exhibited glomerulonephritis and positive PR3-ANCA, but negative for other autoimmune markers.
- Treatment with doxycycline resolved fever and hematuria over 16 months.

## Abstract

Q fever is a zoonotic disease caused by Coxiella burnetii and is endemic worldwide. Q fever endocarditis is commonly found in adults and is rarely seen in children. Infectious endocarditis can also lead to renal damage. Here, we present a case of Q fever endocarditis-associated glomerulonephritis in a Chinese boy with positive Antiproteinase 3 antibody (PR3)-antineutrophil cytoplasmic antibody (ANCA).

A 12-year-old Chinese boy presented with intermittent fever and hematuria for 2 months. He was diagnosed with Tetralogy of Fallot at birth and underwent multiple cardiac surgeries between 1 and 4 years of age. The examinations showed positive serum mycoplasma antibody and increased serum Epstein–Barr virus (EBV) DNA. However, antibiotic and antiviral treatment was not effective. PR3-ANCA antibody was positive (109.8–158.8CU), while anti-myeloperoxidase (MPO) antibody, anti-glomerular basement membrane (GBM) antibody, antinuclear antibodies (ANA), and double-stranded DNA (dsDNA) were negative. Chest CT showed bronchitis. Ophthalmic examination and ENT examinations revealed no abnormalities. Coxiella burnetii was found positive by metagenomics next generation sequencing (mNGS) and immunofluorescence assay (IFA) in the detection of pathogenic microorganisms causing bloodstream infections. Prominent vegetation was present on the pulmonary valve, as demonstrated by cardiac ultrasound. Secondary hyperplastic glomerulonephritis was considered by renal biopsy. Therefore, the final diagnosis was Q fever endocarditis-associated glomerulonephritis. Doxycycline was given to the boy orally and daily, and no fever occurred again. Sixteen months later, hematuria disappeared and PR3-ANCA remainded positive.

Q fever endocarditis should be considered for children presenting with chronic fever, hematuria and positive ANCAs, especially those with a history of congenital heart disease or cardiac operation. It is very helpful for the diagnosis to undergo these examinations, including mNGS, cardiac ultrasound and renal biopsy.