ICU admission and mortality in adult patients with influenza A(H1N1)pdm09-related pneumonia in Vietnam since the 2009 H1N1 pandemic: A 10-year cohort study

Background The A(H1N1)pdm09 virus remains an important cause of severe influenza worldwide. This study examined the burden of ICU admission, mortality, and associated predictors among adults with A(H1N1)pdm09-related pneumonia treated at a leading infectious diseases hospital in Vietnam. Methods Demographic, clinical, laboratory, treatment, and outcome data were retrospectively collected from the medical records of adults hospitalized with laboratory-confirmed A(H1N1)pdm09 infection between 2009 and 2019. Results Among 729 patients with laboratory-confirmed A(H1N1)pdm09 infection, 21.7% (158/729) developed pneumonia. Among patients with pneumonia, 36.7% developed moderate-to-severe acute respiratory distress syndrome, 15.2% required invasive ventilation, 48.7% were admitted to the ICU, and 8.2% died. Independent predictors of ICU admission included age older than 60 years (AOR 18.91, 95% CI 3.60–99.24), the presence of comorbidities (AOR 9.39, 95% CI 2.75–32.06), and laboratory evidence of systemic inflammation, renal dysfunction, and hepatic involvement. Intensified antiviral therapy (AOR = 8.577, 95%CI 1.416–83.341, P = 0.020), and invasive ventilation (AOR 8.426, 95%CI 1.105–141.366, P = 0.039) were independently associated with mortality. Conclusions Mortality associated with A(H1N1)pdm09-related pneumonia remains substantial. Older patients, those with comorbidities, and those presenting with abnormal laboratory findings should be monitored closely for deterioration requiring intensive care. The study did not demonstrate improved outcomes with intensified antiviral regimens. Prospective studies are required before definitive treatment recommendations can be made.