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Another Visit from H1N1

By Amesh A. Adalja, FACP, FACEP, February 21, 2014

The current influenza season has been characterized anecdotally by a high number of young adults presenting with severe disease and requiring ICU admission, which is reminiscent of the 2009 pandemic experience. Though, to date, there is no confirming evidence that the culprit H1N1 virus has undergone a major genetic change, the severity of the illness has nonetheless strained many hospitals and altered policies on patient visitation and use of masks.

Pandemic Similarities in Duke Study

A new study conducted at Duke University, published in the American Journal of Respiratory and Critical Care Medicine, aimed to uncover the characteristics of the seemingly high proportion of influenza patients admitted to ICUs.

This single center study included 55 patients hospitalized with positive PCR results for influenza between November 2013 and January 8, 2014. Several important patient characteristics included:

  • Median age of 28.5 years, (which is similar to the age distribution during the pandemic);

  • 87% infected with H1N1;

  • 60% male;

  • 40% obese by BMI criteria;

  • 42% had pre-existing pulmonary disease;

  • 82% received oseltamivir, though a third received it more than 24 hours after influenza was suspected.

Low Vaccination Rates

Alarmingly, the rate of vaccination among those hospitalized was only 23.6%. Among those admitted to the ICU, as opposed to lower acuity beds, the rate was even lower at 9.1%―a finding that almost reached statistical significance.

ICU Interventions

Of patients admitted to the ICU, approximately 30% required mechanical ventilation, and 73% developed ARDS. ECMO was employed in 31.3% of those who developed ARDS. Rapid influenza tests were negative in 4 of the ICU-admitted patients.

Key Points Highlighted

The study highlights several important points regarding influenza: 1) the importance of vaccination in preventing severe disease; 2) the danger of relying on poorly sensitive rapid influenza tests; and 3) the crucial role of antiviral therapy. As more data from this influenza season become available, it will be important to determine whether Duke's experience is reflective of a general trend.


Catania J, Que LG, Govert JA, et al. High intensive care unit admission rate for 2013-2014 influenza is associated with a low rate of vaccination. Am J Resp Crit Care Med. 2014. 189:485-487.