Abstract:

Objective To investigate the source and transmission dynamics of a varicella zoster virus（VZV） outbreak in a psychiatric hospital in Tianjin，and to identify risk factors contributing to the epidemic. Methods Proactively search for all cases within the hospital that meet the definition of cases and conduct individual case investigations to analyze the distribution characteristics of cases during the epidemic，trace the infection source，and determine transmission routes. Results From February 12th to March 5th，2025，10 varicella cases were identified across two wards. Attack rates were 6.70% in Ward 1 and 2.63% in Ward 3. Gender-specific attack rates were 4.06%（male） and 1.92%（female），while rates by role were 3.00%（patients） and 3.85%（staff）. No statistically significant differences were observed in attack rates by ward，gender，or role（all P>0.05）. Epidemiological tracing identified an index case of herpes zoster（initially misdiagnosed as tinea cruris） in Ward 1 as the outbreak source，a case-control study revealed that using the toilet in the men's restroom in the affected ward was significantly associated with VZV infection（OR=10.261，95%CI：1.088-96.736，P<0.05）. Spread through contact to the three wards，leading to subsequent infections among patients in the same ward. Conclusion This investigation demonstrates that herpes zoster cases can propagate varicella outbreaks，with contact transmission serving as a key mode of spread in this institutional setting. Implementation of strict infection control measures and varicella vaccination programs are critical for outbreak prevention in hospitals.

Key words: Varicella, Psychiatric hospital, Outbreak, Traceability, Herpes zoster