Multiple Estimates of Transmissibility for the 2009 Influenza Pandemic Based on Influenza-like-Illness Data from Small US Military Populations

Rapidly characterizing the amplitude and variability in transmissibility of novel human influenza strains as they emerge is a key public health priority. However, comparison of early estimates of the basic reproduction number during the 2009 pandemic were challenging because of inconsistent data sources and methods. Here, we define and analyze influenza-like-illness (ILI) case data from 2009–2010 for the 50 largest spatially distinct US military installations (military population defined by zip code, MPZ). We used publicly available data from non-military sources to show that patterns of ILI incidence in many of these MPZs closely followed the pattern of their enclosing civilian population. After characterizing the broad patterns of incidence (e.g. single-peak, double-peak), we defined a parsimonious SIR-like model with two possible values for intrinsic transmissibility across three epochs. We fitted the parameters of this model to data from all 50 MPZs, finding them to be reasonably well clustered with a median (mean) value of 1.39 (1.57) and standard deviation of 0.41. An increasing temporal trend in transmissibility (, p-value: 0.013) during the period of our study was robust to the removal of high transmissibility outliers and to the removal of the smaller 20 MPZs. Our results demonstrate the utility of rapidly available – and consistent – data from multiple populations.

快速表征新型人类流感毒株出现时的传播能力振幅与变异性，是公共卫生领域的核心优先事项。然而2009年流感大流行期间，由于数据源与研究方法不统一，早期基本再生数（basic reproduction number）的估算结果难以开展对比分析。本研究针对2009至2010年美国50个空间独立的大型军事基地（按邮政编码划定的军事人口，military population defined by zip code, MPZ）的流感样病例（influenza-like-illness, ILI）数据进行定义与分析。我们采用非军方来源的公开数据，证实这些军事基地的ILI发病模式与其所在民用人口的发病模式高度契合。在明确了发病的整体模式（如单峰、双峰分布）后，我们构建了简约类SIR模型（SIR-like model），该模型在三个时间段内设置了两种不同的固有传播能力参数。我们将该模型的参数拟合至全部50个军事基地的数据集，发现参数呈现出较为显著的聚集性，其中位数（均值）为1.39（1.57），标准差为0.41。研究期间内，传播能力呈现随时间上升的趋势（P值：0.013），该结果在移除高传播能力异常值以及移除规模较小的20个军事基地后依然保持稳健。本研究结果证实了快速获取且标准化的多群体数据的应用价值。