Estimating the Incubation Period Distribution of Psittacosis: A Retrospective Observational Study.

Background and Aims: Human psittacosis is a zoonotic disease mainly transmitted by contact with birds. However, the recently identified potential human-to-human transmission indicated an emerging threat of this disease. This study aimed to estimate the incubation period of confirmed psittacosis cases. Methods: We retrospectively collected epidemiological information on confirmed psittacosis cases in Hangzhou City, Zhejiang Province, China, during 2022-2024. Incubation period distributions were estimated from interval-censored exposure and illness onset data using Bayesian parametric models and the Turnbull nonparametric maximum likelihood method. Results: The median incubation period of confirmed psittacosis cases was 11.3 (95% CrI: 8.5-14.2) days with a 95th percentile of 21.8 (95% CrI: 17.8-28.3) days. Conclusion: These estimates could inform clinical diagnosis and would be an important input into mathematical models.