Despite an enormous global investment in preparing for the reemergence of 2009 influenza A(H1N1), preparations proceeded largely without empirical data about the nature and severity of disease. This paucity of data is particularly problematic for clinicians in intensive care units (ICUs), who will shoulder a heavy burden for the clinical response to H1N1. In this issue of JAMA, 3 reports provide data that begin to fill this empirical void.
Domínguez-Cherit and colleagues1 conducted an observational study of 58 patients admitted to 6 ICUs in Mexico City with H1N1-related disease during the initial outbreak in spring 2009. Kumar and colleagues2 conducted a similar study of 168 critically ill patients in 38 Canadian ICUs. There were striking similarities in the main findings. Patients tended to be relatively healthy adolescents and young adults who developed a brief prodromal illness followed by rapidly progressive respiratory failure. Shock and multisystem organ failure were common. Hypoxemia was prolonged and severe, requiring on average 12 days of mechanical ventilation and frequent use of rescue therapies such as high-frequency oscillatory ventilation, prone positioning, neuromuscular blockade, and inhaled nitric oxide. The influenza outbreak lasted about 3 months in both countries, but the peak lasted just a few weeks, during which time hospitals struggled to accommodate the increased patient load, with 4 Mexican patients dying while awaiting ICU beds. Notably, the Mexican cohort incurred a mortality rate twice as high as that in Canada. In contrast to the high rates of health care worker infections during severe acute respiratory syndrome (SARS) outbreaks,3 there were no documented cases of nosocomial transmission in either series.