Objectives

Excess population mortality during winter is most often associated with influenza A(H3N2), though susceptibility differs by age. We examined differences between influenza types/subtypes in their association with severe laboratory-confirmed cases, overall and by age group, to determine which type is the most virulent.

Methods

We used nine seasons of comprehensive nationwide surveillance data from Greece (2010–2011 to 2018–2019) to examine the association, separately for influenza A(H1N1)pdm09, A(H3N2) and B, between the number of laboratory-confirmed severe cases (intensive care hospitalizations or deaths) per type/subtype and the overall type-specific circulation during the season (expressed as a cumulative incidence proxy). Quasi-Poisson models with identity link were used, and multiple imputation to handle missing influenza A subtype.

Results

For the same level of viral circulation and across all ages, influenza A(H1N1)pdm09 was associated with twice as many intensive care hospitalizations as A(H3N2) (rate ratio (RR) 1.89, 95% CI 1.38–2.74) and three times more than influenza B (RR 3.27, 95%CI 2.54–4.20). Similar associations were observed for laboratory-confirmed deaths. A(H1N1)pdm09 affected adults over 40 years at similar rates, whereas A(H3N2) affected elderly people at a much higher rate than younger persons (≥65 vs. 40–64 years, RR for intensive care 5.42, 95% CI 3.45–8.65, and RR for death 6.19, 95%CI 4.05–9.38). Within the 40–64 years age group, A(H1N1)pdm09 was associated with an approximately five times higher rate of severe disease than both A(H3N2) and B.

Discussion

Influenza A(H1N1)pdm09 is associated with many more severe laboratory-confirmed cases, likely due to a more typical clinical presentation and younger patient age, leading to more testing. A(H3N2) affects older people more, with cases less often recognized and confirmed.

中文翻译：

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特定类型的流感传播与严重的实验室确诊病例的发生率之间的关联；哪种亚型最强？

目标

尽管易感性因年龄而异，但冬季过高的人口死亡率通常与甲型H3N2流感有关。我们检查了流感类型/亚型之间的差异，以及在总体上和按年龄组划分的严重实验室确诊病例的相关性，以确定哪种类型是最致命的。

方法

我们使用了从希腊（2010-2011年至2018-2019年）的九个季度的全国范围全面监视数据，分别检查了实验室确诊的严重病例数与甲型（H1N1）pdm09，甲型（H3N2）和乙型流感的相关性（每个类型/亚型的重症监护住院或死亡人数）和整个季节中特定类型的总体流通量（表示为累积发病率指标）。使用具有身份链接的准Poisson模型，并多次插补处理缺失的A型流感亚型。

结果

对于相同水平且在所有年龄段的病毒循环，A（H1N1）pdm09流感的重症监护住院率是A（H3N2）的两倍（比率（RR）1.89、95％CI 1.38–2.74）和三倍。高于乙型流感（RR 3.27，95％CI 2.54–4.20）。在实验室确认的死亡中也观察到类似的关联。A（H1N1）pdm09影响40岁以上成年人的发生率相似，而A（H3N2）影响老年人的发生率远高于年轻人（≥65vs. 40-64岁，重症监护室的相对危险度5.42，95％CI 3.45 –8.65，死亡的RR为6.19，95％CI 4.05–9.38）。在40-64岁年龄组中，A（H1N1）pdm09与A（H3N2）和B的严重疾病发生率相比大约高五倍。

讨论

甲型（H1N1）pdm09流感与许多更严重的实验室确诊病例有关，可能是由于临床表现更为典型，患者年龄更年轻，导致需要进行更多的检测。A（H3N2）对老年人的影响更大，病例很少被识别和确认。