Abstract
In this study, estimates of the growth rate of new infections, based on the growth rate of new laboratory-confirmed cases, were used to provide a statistical basis for in-depth research into the epidemiological patterns of H7N9 epidemics. The incubation period, interval from onset to laboratory confirmation, and confirmation time for all laboratory-confirmed cases of H7N9 avian influenza in Mainland China, occurring between January 2013 and June 2017, were used as the statistical data. Stochastic processes theory and maximum likelihood were used to calculate the growth rate of new infections. Time-series analysis was then performed to assess correlations between the time series of new infections and new laboratory-confirmed cases. The rate of new infections showed significant seasonal fluctuation. Laboratory confirmation was delayed by a period of time longer than that of the infection (average delay, 13 days; standard deviation, 6.8 days). At the lags of −7.5 and −15 days, respectively, the time-series of new infections and new confirmed cases were significantly correlated; the cross correlation coefficients (CCFs) were 0.61 and 0.16, respectively. The temporal distribution characteristics of new infections and new laboratory-confirmed cases were similar and strongly correlated.
Highlights
In March 2013, a new type of avian influenza virus, H7N9, was isolated for the first time in China[1]
Because infection occurs before the diagnosis is made, assessing the epidemic trend using the growth rate of confirmed cases is imprecise; we consider the growth rate of new infections an important indicator of the seriousness of an epidemic
Our goal was to treat all laboratory-confirmed cases between January 2013 and June 2017 as a sample with number N, and to use this sample to estimate the temporal distribution for the growth rate of new infections
Summary
In March 2013, a new type of avian influenza virus, H7N9, was isolated for the first time in China[1]. The fifth epidemic was the most severe; cases were diagnosed in 20 provinces and the total number of cases exceeded the sum of the previous 4 epidemics[3] These 5 epidemics occurred mostly in China’s Yangtze and Pearl River Deltas[3]. Lin et al.[14] modelled chicken-to-chicken transmission and found that environmental transmission via viral shedding by infected chickens contributed to the spread of the virus. These studies help us to understand the prevalence of the virus among poultry and the mechanisms of its transmission from poultry to humans. No studies have yet been published on the evolutionary mechanism of the entire process from infection to symptom onset to diagnosis
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