ICU Admissions Up During Flu Season Down Under

The number of patients infected with pandemic influenza A(H1N1) who required intensive care this past winter in Australia and New Zealand was 15 times the number admitted to an ICU with viral pneumonitis in recent years.

Admission to the ICU was especially high among H1N1-infected patients who were younger than 1 year, pregnant women, people with a body mass index greater than 35 kg/m

The data came from a review of 722 patients admitted to an ICU from June through August with a confirmed diagnosis of pandemic H1N1 infection. During each winter of the preceding 4 years, an average of 57 patients with viral pneumonitis required ICU admission. The peak of ICU admissions occurred about 4–6 weeks following the first confirmed ICU admission of an H1N1 patient.

The incidence of ICU admissions was more than 70 per million inhabitants among infants younger than 1 year, substantially greater than the 20–40 admissions per million in any other age category.

The highest number of ICU admissions occurred among patients aged 25–49—about 300 patients, or more than 40% of the total.

Pregnant women constitute about 1% of the population in the two countries, but formed 9% of the ICU admissions. People with a BMI over 35 are about 5% of the population but made up 29% of the ICU admissions. The ICU admission rate for people with asthma or another chronic pulmonary disease was roughly threefold higher than expected based on the prevalence of these disorders.

Of patients who needed intensive care, 32% had no predisposing factor, 49% had acute respiratory disease or viral pneumonitis, and 20% were clinically diagnosed with bacterial pneumonia.

The median duration of hospitalization was 12 days, and the median duration of ICU treatment was 7 days. Treatment with a mechanical ventilator occurred in 65% of the ICU patients, for a median of 8 days.

By Sept. 7, 17% of the ICU-treated patients had died. Virtually all deaths occurred while patients were hospitalized. Patients with seasonal influenza who required ICU admission had similar mortality, the authors said.

Three factors were independently associated with an increased risk of death during hospitalization: need for invasive ventilation at ICU admission (5.5-fold increased risk), a coexisting condition (2.5-fold increased risk), and age (2% increase for each year of age).