Risk factors for adult death due to 2009 pandemic influenza A (H1N1) virus infection: a 2151 severe and critical cases analysis

Background The 2009 pandemic H1N1 (pH1N1) influenza showed that relatively young adults accounted for the highest rates of hospital admission and death. In preparation for pH1N1, the aim of the study is to identify factors associated with the mortality of patients with 2009 pH1N1 infection, especially for young patients without chronic medical conditions. Methods Retrospective observational study of 2151 severe or critical adult cases (>= 14 years old) admitted to a hospital with pH1N1 influenza from September 1, 2009 to December 31, 2009 from 426 hospitals of 27 Chinese provinces. A confirmed case was a person whose pH1N1 virus infection was verified by real-time reverse-transcriptase polymerase chain reaction (rRT-PCR). Severe and critical cases were defined according to the H1N1 2009 Clinical guidelines (Third Edition, 2009) released by the Ministry of Health of China. Results Among the 2151 patients, the mean age was 34.0 years. Two hundred and ninty-three (13.6%) died during hospital stay. One thousand four hundred and forty-two patients (67.0%) had no comorbidities and 189 (13.1%) of them died. Pregnancy (OR 8.03), pneumonia (OR 8.91), dyspnea (OR 3.95), central nervous system (CNS) symptom (OR 1.55), higher APACHE (Acute Physiology and Chronic Health Evaluation) II score (OR 1.06), Alanine aminotransferase (ALT) (OR 1.002), and the lactate dehydrogenase (LDH) level (OR 1.001) were independent risk factors for death among adults without chronic medical conditions. Higher APACHE II score (OR 1.08) and age (OR 1.06) were independent risk factors for death among adults with respiratory diseases. A multivariate analysis showed an association between mortality and CNS symptoms (OR 2.66), higher APACHE II score (OR 1.03), ALT (OR 1.006), and LDH level (OR 1.002) in patients with cardiovascular diseases. Dyspnea (OR 11.32) was an independent risk factor for patient death in patients with diabetes mellitus. Conclusion Clinical knowledge of identified prognostic factors for mortality may aid in the management of adult influenza infection.