H1N1 causing critical illness mostly in young adults

Kathleen Blanchard's picture
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A review of H1N1 flu shows that the virus is causing critical illness mostly in young adults. H1N1 flu in young adults is associated with low levels of oxygen, multi-system organ failure, and the need for longer prolonged respiratory support with mechanical ventilation. The findings are due for publication November 4 in JAMA, and show that H1N1 flu is especially severe among healthy adolescents and adults between the ages of 10 and 60 years.

The authors write that H1N1 flu follows”… a pattern reminiscent of the W-shaped curve [rise and fall in the population mortality rate for the disease, corresponding to age at death] previously seen only during the 1918 H1N1 Spanish pandemic."

Anand Kumar, M.D., of the Health Sciences Centre and St. Boniface Hospital, Winnipeg, Manitoba, Canada, and colleagues with the Canadian Critical Care Trials Group H1N1 Collaborative conducted observational studies of H1N1 flu between April 16 and August 12, 2009, looking primarily at death rates, admission to ICU’s (pediatric and adult), and frequency of mechanical ventilation in 38 facilities in Canada. They found that H1N1 is causing critical illness in primarily young adults.

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The study investigators found a total of 168 patients who had either confirmed swine flu or were likely to have H1N1 flu and became critically ill. Fifty of the patients investigated were children.

The average age was 32.3. Most were admitted to the hospital after four days of onset of H1N1 flu, and then became rapidly and critically ill within two days, necessitating admission to intensive care – 136 were placed on ventilators. Twenty four patients died within 28 days of becoming seriously ill from multi-system organ failure and shock. Five more patients died within 90 days.

One of the fears expressed in an accompanying editorial from Douglas B. White, M.D., M.A.S., and JAMA Contributing Editor Derek C. Angus, M.D., M.P.H., of the University of Pittsburgh School of Medicine is that hospitals may not be adequately prepared to treat the most critically ill patients admitted with H1N1 flu. "Hospitals must develop explicit policies to equitably determine who will and will not receive life support should absolute scarcity occur. Any deaths from 2009 influenza A (H1N1) will be regrettable, but those that result from insufficient planning and inadequate preparation will be especially tragic,"

The researchers concluded that swine flu primarily affects young adults who are relatively health and free of underlying illnesses. H1N1 flu is “associated with severe hypoxemic respiratory failure, often requiring prolonged mechanical ventilation and rescue therapies," the authors write. H1N1 flu has affected mostly young adults, causing critical illness and ICU admissions.

JAMA. 2009;302(17):doi:10.1001/jama.2009.1496

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