Data from: Association between the severity of influenza A(H7N9) virus infections and length of the incubation period

Background: In early 2013, a novel avian-origin influenza A(H7N9) virus emerged in China, and has caused sporadic human infections. The incubation period is the delay from infection until onset of symptoms, and varies from person to person. Few previous studies have examined whether the duration of the incubation period correlates with subsequent disease severity. Methods and Findings: We analyzed data of period of exposure on 395 human cases of laboratory-confirmed influenza A(H7N9) virus infection in China in a Bayesian framework using a Weibull distribution. We found a longer incubation period for the 173 fatal cases with a mean of 3.7 days (95% credibility interval, CrI: 3.4–4.1), compared to a mean of 3.3 days (95% CrI: 2.9–3.6) for the 222 non-fatal cases, and the difference in means was marginally significant at 0.47 days (95% CrI: -0.04, 0.99). There was a statistically significant correlation between a longer incubation period and an increased risk of death after adjustment for age, sex, geographical location and underlying medical conditions (adjusted odds ratio 1.70 per day increase in incubation period; 95% credibility interval 1.47–1.97). Conclusions: We found a significant association between a longer incubation period and a greater risk of death among human H7N9 cases. The underlying biological mechanisms leading to this association deserve further exploration.

背景：2013年初，中国首次出现新型禽源甲型H7N9流感病毒（novel avian-origin influenza A(H7N9) virus），并引发散发性人感染病例。潜伏期（incubation period）指从病毒感染至症状发作的间隔时长，个体间存在差异。既往鲜有研究探讨潜伏期时长与后续疾病严重程度的相关性。
方法与结果：本研究采用贝叶斯框架（Bayesian framework）结合威布尔分布（Weibull distribution），对中国境内395例经实验室确诊的甲型H7N9流感病毒感染人病例的暴露时段数据进行分析。结果显示，173例死亡病例的潜伏期更长，平均时长为3.7天（95%可信区间（credibility interval）：3.4~4.1）；而222例非死亡病例的平均潜伏期为3.3天（95%可信区间：2.9~3.6），两组均值差异为0.47天（95%可信区间：-0.04~0.99），仅存在边际显著性。在校正年龄、性别、地理位置及基础疾病状况后，潜伏期延长与死亡风险升高呈显著统计学相关（每增加1天潜伏期，校正比值比（adjusted odds ratio）为1.70；95%可信区间：1.47~1.97）。
结论：本研究发现，人感染H7N9流感病例中，潜伏期更长与死亡风险升高存在显著关联。介导该关联的潜在生物学机制有待进一步探究。