Influenza A (H1N1) 2009 pandemic: was there a difference in the two waves in patients requiring admission to the intensive-care unit?

Influenza virus is prone to mutations that may alter the intensity of subsequent waves of infection. In this study, we evaluated whether outcomes were different in the two waves of the influenza A (H1N1) 2009 pandemic in patients admitted to the intensive-care unit. Age, gender, lag-time to presentation and APACHE-II scores were similar in both waves. Although ventilatory requirements were similar (36/37 vs. 36/39), non-significant reductions in the durations (days) of ventilation (10.3 ± 8.0 vs. 7.8 ± 9.4, p 0.11) and hospitalization (14.9 ± 10.5 vs. 12.3 ± 14.1, p 0.20) were observed in the second wave. The clinical profile and outcomes were not significantly different between the two waves among severely ill patients.