Table 1_Epidemiological characteristics and environmental surveillance of human psittacosis in Lishui City, Zhejiang Province, China (2021–2024).docx

IntroductionPsittacosis, caused by Chlamydia psittaci, is an underdiagnosed zoonosis that can lead to severe pneumonia and fatal outcomes. In China, traditional poultry farming poses substantial risks for avian-to-human transmission, yet comprehensive epidemiological evidence is scarce. To address this gap, we aimed to define the local epidemiology, risk factors, and environmental reservoirs of human psittacosis in Lishui City, Zhejiang Province.
MethodsWe conducted a multi-source epidemiological study (2021–2024) integrating surveillance data, clinical records, contact investigations, and environmental sampling. Cases were confirmed by quantitative polymerase chain reaction (qPCR) or metagenomic next-generation sequencing (mNGS).
ResultsWe identified 28 laboratory-confirmed cases, showing annual fluctuations in reported case numbers. Infections, mostly confirmed by mNGS, were predominantly sporadic among elderly agricultural workers (mean age 62.6 years), with 96.4% reporting recent poultry exposure. All patients presented with pneumonia; 64.3% developed severe disease, resulting in three deaths. The median diagnostic delay—from symptom onset to diagnosis—was 12 days. A household cluster of three cases was detected; however, no secondary transmission occurred among 205 close contacts outside the household. C. psittaci DNA was detected in 14.79% (21/142) of environmental samples, with the highest number of cases detected in duck manure samples, with the highest positive rate (26.7%). Phylogenetic analysis of 20 ompA gene sequences revealed a predominantly genotype A and the waterfowl-TW genotype, which are closely related to strains from southern China.
DiscussionPsittacosis in Lishui presents as a sporadic but clinically severe disease in older rural residents. The high frequency of severe pneumonia and prolonged diagnostic delay underscores an urgent need to improve clinical suspicion and access to molecular diagnostics. Detection of C. psittaci nucleic acid in environmental samples suggests possible environmental contamination; however, viability and transmissibility were not assessed.