Household cluster of psittacosis caused by Chlamydia psittaci ST388 in China: a case report and genomic analysis.

In March 2025, a married couple in Jiaxing City, Zhejiang Province, China, presented with fever and pneumonia. Metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage fluid confirmed Chlamydia psittaci (C. psittaci) infection. Epidemiological investigation revealed exposure to a pet budgerigar purchased one month prior. Environmental sampling detected C. psittaci in the bird's feces and the patients' living spaces. Phylogenetic analysis of the ompA gene identified the strains as genotype A, and multilocus sequence typing (MLST) determined the sequence type (ST) as ST388. Two cohabiting elderly parents without bird exposure remained asymptomatic and PCR-negative. Phylogenetic analysis showed the avian and environmental isolates formed a distinct clonal cluster. This report highlights the risk of zoonotic transmission from asymptomatic avian carriers and the utility of genomic surveillance in outbreak investigation. Clinicians should consider psittacosis in atypical pneumonia cases with bird exposure.