Comparative analysis of clinical features and risk factors of severe pneumonia development in pediatric patients hospitalized with seasonal influenza or swine-origin influenza infection.

BACKGROUND The influenza A virus is the most important human pathogen affecting respiratory tract in children and has been prevalent for more than a century. OBJECTIVES To describe epidemiological and clinical features in hospitalized children with acute respiratory infection caused by a novel swine-origin influenza virus (S-OIV) and seasonal influenza virus A (IVA). MATERIAL AND METHODS A total of 1,074 nasopharyngeal aspirate (NPA) samples were collected from children hospitalized with acute respiratory tract infections. The RNAs of S-OIV and seasonal IVA in the samples were examined using real-time polymerase chain reaction (RT-PCR). RESULTS The presence of IVA was detected in 105 samples (9.8%), including S-OIV in 15 samples (1.4%) and seasonal IVA in the remaining samples (8.4%). The incidence of both viral infections was lower in autumn and winter. The rates of severe pneumonia in patients with S-OIV and seasonal IVA were 6.7% and 15.6%, respectively. In total, 14 out of 90 seasonal IVA-positive cases were categorized as severe pneumonia and 1 out of 15 S-OIV-positive cases as severe bronchiolitis. Five samples were found to have single S-OIV infection among 15 S-OIV-positive cases, while other respiratory viruses were detected in the other 9 samples. Twenty-one samples were found to be single seasonal-IVA-positive among the 90 seasonal-IVA-positive cases. Underlying heart conditions (odds ratio (OR) = 13.60), wheezing (OR = 6.82) and co-infection with adenovirus (OR = 6.21) were risk factors for developing severe pneumonia in seasonal IVA patients. CONCLUSIONS Children younger than 2 years appeared to be susceptible to both kinds of viral infection. Diagnoses of non-severe respiratory tract infection were mainly made for patients with S-OIV and IVA infection. Underlying heart conditions, wheezing and co-infection with adenovirus increase the risk of developing severe pneumonia in seasonal IVA patients.