Research Institute of The Hospital for Sick Children, and the Dalla Lana School of Public Health, Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario.
CMAJ. 2010 Feb 9;182(2):131-6. doi: 10.1503/cmaj.091807. Epub 2009 Dec 3.
In the face of an influenza pandemic, accurate estimates of epidemiologic parameters are required to help guide decision-making. We sought to estimate epidemiologic parameters for pandemic H1N1 influenza using data from initial reports of laboratory-confirmed cases.
We obtained data on laboratory-confirmed cases of pandemic H1N1 influenza reported in the province of Ontario, Canada, with dates of symptom onset between Apr. 13 and June 20, 2009. Incubation periods and duration of symptoms were estimated and fit to parametric distributions. We used competing-risk models to estimate risk of hospital admission and case-fatality rates. We used a Markov Chain Monte Carlo model to simulate disease transmission.
The median incubation period was 4 days and the duration of symptoms was 7 days. Recovery was faster among patients less than 18 years old than among older patients (hazard ratio 1.23, 95% confidence interval 1.06-1.44). The risk of hospital admission was 4.5% (95% CI 3.8%-5.2%) and the case-fatality rate was 0.3% (95% CI 0.1%-0.5%). The risk of hospital admission was highest among patients less than 1 year old and those 65 years or older. Adults more than 50 years old comprised 7% of cases but accounted for 7 of 10 initial deaths (odds ratio 28.6, 95% confidence interval 7.3-111.2). From the simulation models, we estimated the following values (and 95% credible intervals): a mean basic reproductive number (R0, the number of new cases created by a single primary case in a susceptible population) of 1.31 (1.25-1.38), a mean latent period of 2.62 (2.28-3.12) days and a mean duration of infectiousness of 3.38 (2.06-4.69) days. From these values we estimated a serial interval (the average time from onset of infectiousness in a case to the onset of infectiousness in a person infected by that case) of 4-5 days.
The low estimates for R0 indicate that effective mitigation strategies may reduce the final epidemic impact of pandemic H1N1 influenza.
面对流感大流行，需要准确估计流行病学参数，以帮助指导决策。我们试图使用确诊病例的初始报告中的数据来估计大流行 H1N1 流感的流行病学参数。
我们获得了加拿大安大略省报告的实验室确诊大流行 H1N1 流感病例的数据，其症状发作日期在 2009 年 4 月 13 日至 6 月 20 日之间。潜伏期和症状持续时间估计并拟合为参数分布。我们使用竞争风险模型估计住院风险和病死率。我们使用马尔可夫链蒙特卡罗模型来模拟疾病传播。
潜伏期中位数为 4 天，症状持续时间为 7 天。年龄小于 18 岁的患者比年龄较大的患者恢复更快（危险比 1.23，95%置信区间 1.06-1.44）。住院风险为 4.5%（95%CI 3.8%-5.2%），病死率为 0.3%（95%CI 0.1%-0.5%）。住院风险最高的是年龄小于 1 岁和 65 岁或以上的患者。年龄大于 50 岁的成年人占病例的 7%，但占 10 例初始死亡中的 7 例（比值比 28.6，95%置信区间 7.3-111.2）。从模拟模型中，我们估计了以下值（和 95%可信区间）：平均基本繁殖数（R0，易感人群中由单个原始病例产生的新病例数）为 1.31（1.25-1.38），平均潜伏期为 2.62（2.28-3.12）天，平均传染性持续时间为 3.38（2.06-4.69）天。根据这些值，我们估计了一个序列间隔（从病例的传染性开始到该病例感染的人开始出现传染性的平均时间）为 4-5 天。
R0 的低估计表明，有效的缓解策略可能会降低大流行 H1N1 流感的最终流行影响。
