title: Estimating the Distribution of the Incubation Periods of Human Avian Influenza A(H7N9) Virus Infections.
abstract: A novel avian influenza virus, influenza A(H7N9), emerged in China in early 2013 and caused severe disease in humans, with infections occurring most frequently after recent exposure to live poultry. The distribution of A(H7N9) incubation periods is of interest to epidemiologists and public health officials, but estimation of the distribution is complicated by interval censoring of exposures. Imputation of the midpoint of intervals was used in some early studies, resulting in estimated mean incubation times of approximately 5 days. In this study, we estimated the incubation period distribution of human influenza A(H7N9) infections using exposure data available for 229 patients with laboratory-confirmed A(H7N9) infection from mainland China. A nonparametric model (Turnbull) and several parametric models accounting for the interval censoring in some exposures were fitted to the data. For the best-fitting parametric model (Weibull), the mean incubation period was 3.4 days (95% confidence interval: 3.0, 3.7) and the variance was 2.9 days; results were very similar for the nonparametric Turnbull estimate. Under the Weibull model, the 95th percentile of the incubation period distribution was 6.5 days (95% confidence interval: 5.9, 7.1). The midpoint approximation for interval-censored exposures led to overestimation of the mean incubation period. Public health observation of potentially exposed persons for 7 days after exposure would be appropriate.
authors.forename: Victor
authors.initials: V
authors.lastname: Virlogeux
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.forename: Tim K
authors.initials: TK
authors.lastname: Tsang
authors.forename: Luzhao
authors.initials: L
authors.lastname: Feng
authors.forename: Vicky J
authors.initials: VJ
authors.lastname: Fang
authors.forename: Hui
authors.initials: H
authors.lastname: Jiang
authors.forename: Peng
authors.initials: P
authors.lastname: Wu
authors.forename: Jiandong
authors.initials: J
authors.lastname: Zheng
authors.forename: Eric H Y
authors.initials: EH
authors.lastname: Lau
authors.forename: Yu
authors.initials: Y
authors.lastname: Cao
authors.forename: Ying
authors.initials: Y
authors.lastname: Qin
authors.forename: Qiaohong
authors.initials: Q
authors.lastname: Liao
authors.forename: Hongjie
authors.initials: H
authors.lastname: Yu
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Cowling
mesh_terms: D002681:China / Q000453:epidemiology; D004196:Disease Outbreaks / Q000517:prevention & control; D005260:Female; D006801:Humans; D055256:Infectious Disease Incubation Period; D064766:Influenza A Virus, H7N9 Subtype / Q000302:isolation & purification / Q000472:pathogenicity*; D007251:Influenza, Human / Q000453:epidemiology* / Q000401:mortality / Q000517:prevention & control; D053208:Kaplan-Meier Estimate; D008297:Male; D008432:Mathematical Computing; D008875:Middle Aged; D015233:Models, Statistical
keywords: incubation period; influenza; influenza A virus; influenza A(H7N9)