Histopathologic changes of the placenta in Q fever infection: An Australian case series

Q fever is a zoonotic infectious disease with a particular tropism for the placenta. Some studies have suggested associated adverse outcomes including intrauterine growth restriction (IUGR) and intrauterine fetal demise (IUFD). Despite this, data on corresponding histologic features of the placenta are sparse. The aim of this study was to describe histopathologic findings of the placenta in cases of Q fever infection with their associated pregnancy outcomes.

Patients were identified in a database search of Queensland cases between January 2000 and January 2025. The study was inclusive of all patients with a confirmed diagnosis of Q fever through serological or PCR testing, and placental histopathology performed. Histopathologic features of the placenta were reviewed and described based on slides and reports. Epidemiologic, clinical and microbiologic data was also extracted and described.

Ten patients were identified, including four asymptomatic infections, two partially treated infections, and four treated infections. PCR testing of the placenta was performed in all cases, and was positive in all untreated infections, and one partially treated infection. These PCR positive cases showed distinct findings, with a florid acute villitis and intervillositis, abscess formation and decidual necrosis. One partially treated infection showed atypical features including a chronic villitis and chorionic plate inflammation with giant cells. The treated and placental PCR negative cases did not show any specific abnormalities.

This study finds a specific histologic appearance associated with untreated Q fever infection and poor outcomes in pregnancy. The histologic findings described should prompt reflex Q fever testing.