The relationship between the cumulative numbers of cases and deaths reveals the confirmed case fatality ratio of a novel influenza A (H1N1) virus.

摘要

When a novel influenza virus emerges, it is crucial to gain an understanding of the virulence at the very early stage of a pandemic. If a high mortality is predicted, then corresponding countermeasures can be chosen and implemented, and the extent of the pandemic in the presence and absence of interventions is subsequently estimated. In the ongoing pandemic involving the influenza A (H IN 1) virus 2009, such an early assessment was initially made based on confirmed cases whose risk of death was estimated at up to 0.5% (1-3). Although it later appeared that the risk of death among all symptomatic cases with medical attendance (i.e., symptomatic case fatality ratio [sCFR]) ranged from approximately 0.02-0.05% (4,5), a ratio which is more useful for the assessment of virulence and prediction of the mortality impact, epidemiologi-cal interpretation of minimally available data during the very early stages of the pandemic in the present study involves confirmed cases alone.