H1N1 learnings: Risk factors for severe outcomes among patients admitted to hospital with H1N1

A new study in CMAJ (Canadian Medical Association Journal) of all patients in Canada admitted to hospital for H1N1 in the first five months of the outbreak summarizes the risk factors for a severe outcome. The H1N1 pandemic presents important learnings for clinicians and researchers and data on severe outcomes can help inform future treatment and prevention guidelines.

The risk of a severe outcome among patients admitted to hospital with H1N1 was elevated among those who had an underlying medical condition and patients 20 years of age and older. Patients aged 65 years and older were at the greatest risk for death.

"All 13 provinces and territories in Canada participated in an active national surveillance system that captured all cases of laboratory-confirmed 2009 pandemic (H1N1) influenza in patients admitted to hospital or who died and then reported them to the Public Health Agency of Canada," write Dr. Rachel Rodin, Public Health Agency of Canada and coauthors. "The ability to gather detailed, case-based information rapidly and in a relatively uniform manner across Canada reflects an important partnership between provincial, territorial and federal public health authorities."

The study looked at 1479 people admitted to hospital, including the ICU, with confirmed H1N1. It found the risk of death increased by 5.5% with a delay of one day in the time between when the symptoms started and when the patient was admitted to the hospital. The risk of a severe outcome remained constant over a five-month period.

The authors conclude that as the pandemic evolves, continued investigation of risk factors for severe outcomes is needed to provide timely evidence to inform the development and updating of clinical and public health guidelines.