Pregnant women, infants and obese at highest risk

RICHMOND – An evaluation of 1088 hospitalisations due to H1N1 swine flu in California suggests that the new pandemic affects predominantly young patients. The surprising results of a newly published study include the finding that a majority of patients seem to have comorbidities not considered as classical risk factors for severe influenza. Hypertension and obesity are prominent among these, report physicians from the California Department of Public Health, writing in the Journal of the American Medical Association ( JAMA ).

Calling attention to this new phenomenon, Dr Janice Louie and colleagues add: “Further investigation is needed to clarify the association between obesity and severe influenza and the pathophysiology underlying any association”.

Pandemic influenza A (H1N1) emerged rapidly in California in April 2009. Preliminary comparison with seasonal influenza suggests that the pandemic strain disproportionately affects younger people.

The new study looked at patients with confirmed H1N1 infection reported to the California Department of Public Health between April 23 and August 11, 2009. The median age was 27 years and 68% had classical risk factors for seasonal influenza complications. One in three patients was less than 18 years old. When infants were infected, they frequently needed hospitalisation.

Not only did 31% of hospitalised patients subsequently have to be admitted to the intensive care unit, often in need of mechanical ventilation, but there was a high overall - fatality rate of 11% (118 cases).

Patients aged 50 or older who were hospitalised with the infection were among those most likely to die. As many as one in five of these patients died from complications such as acute respiratory distress syndrome.

Infants, a group with the highest hospitalisation rates, are too young for currently approved vaccinations. Dr. Louie and colleagues state that people in close contact with young infants must therefore be vaccinated.

The authors also suggest that swine flu can be difficult to diagnose: rapid antigen tests were falsely negative in 34% of the evaluated cases.
“The median age (27 years) was lower than with seasonal influenza,“ comments Dr. Louie. “While most patients had symptoms of an acute respiratory illness, more than one third of patients reported gastrointestinal symptoms such as nausea or vomiting.

Antiviral treatment can reduce mortality even if initiated late, so that according to current US guidelines every hospitalised patient should receive a neuraminidase inhibitor, regardless of when symptoms started”.

Picture credit: NIAID via Wikimedia Commons