Older Hospitalized Flu Patients Less Likely to Enter ICU

Older age was a risk factor for death for patients who were hospitalized with seasonal influenza, according to a new report. However, older age was also associated with a lower risk of admission to the intensive care unit.

Investigators from the University of Barcelona conducted an observational study of adult patients in 12 hospitals in Spain between 2010 and 2016. They aimed to identify the factors linked to ICU admission or death in hospitalized patients based on the influenza viral type and subtype. Seasonal influenza is a common cause of hospitalizations in patients with underlying disease or older age, and they wanted to further understand the differences in severity based on the types and subtypes of the viruses, they wrote.

The researchers identified a total of 1726 patients and collected data based on age, sex, comorbid disorders, date of symptom onset, hospital stay, flu vaccine status, date of antiviral treatment, ICU admission, death, and type of virus (either influenza A or B) as well as subtype (either H1N1pdm09 or H3N2).

The patients were classified as vaccinated if they had received a dose more than 14 days prior to symptom onset, the investigators added.

During the study, 595 patients—about a third—were admitted to the ICU, while 224 patients (13%) died. The majority of the cases were influenza A, which infected 85.9% of patients. Of those patients, about half had the H1N1 subtype, a quarter had the H3N2 subtype, and the other quarter were not subtyped.

Of the influenza A patients, about a third required ICU admission and 13% died. Those aged between 65-74 years and those over 75 years were associated with a lower ICU admission risk. Higher age was associated with an increased risk of death, and so was having underlying conditions such as chronic cardiovascular disease and chronic liver disease. Vaccination was also associated with lower ICU admission and antiviral treatment was associated with a lower risk of death. The investigators also observed that male sex and obesity were linked to ICU admission.

Among influenza A patients with the H1N1 and H3N2 subtypes, age ≥75 years was associated with lower ICU admission. Additionally, among both subtypes, age between 65-74 and patients ≥75 years were associated with an increased risk of death, the study authors wrote.

Influenza B infected 243 patients. Of those, 75 required ICU admission and 31 died. In this group, the investigators found, age ≥75 years was associated with a lower risk of ICU admission again. Comorbidities such as COPD were linked to ICU admission, though cardiovascular disease was associated with lower ICU admission, they said.

Other factors that led to increased risk of death in patients with influenza type B included age between 65-74 years or older than 75 years, as well as chronic renal disease or immune deficiency.

“Our results suggest that predictors of poor outcomes of influenza may vary by type/subtypes,” the investigators concluded. “Older age was a differential factor in patients hospitalized due to severe influenza with respect to ICU admission and death. While age ≥65 years was a risk factor for death in all influenza types and subtypes, and especially for type B, age >75 years was associated with lower ICU admission for all influenza types and subtypes. The comorbidity with the closest association with death was immune deficiency, mainly in type B patients.”

The paper, “Risk factors associated with severe outcomes in adult hospitalized patients according to influenza type and subtype,” was published in PLOS ONE.