Risk factors for severe influenza A virus infections in post-2009 pandemic period

Literature data concerning risk factors for severe influenza in post-2009 pandemic period, from low- and middle-income Central and Eastern European countries are very limited. The aim of this study was to investigate the risk factors for severe A(H1N1)pdm09 and A(H3N2) influenza during the post-2009 pandemic period. During four consecutive seasons of 2010/2011–2013/2014, nasopharyngeal or nasal and pharyngeal swab samples from 153 patients with mild and 147 patients with severe influenza were tested using real-time reverse transcription polymerase chain reaction (real-time RT PCR) assays. The study indicated three statistically significant risk factors of influenza severity, including presence of chronic underlying illness/condition [odds ratio (OR) of 15.2, 95% confidence interval (CI) of 1.8–125.4, p = 0.001), age ≥15 years (OR 9.2, 95% CI 3.5–24.1, p < 0.001), and delay in medical care of more than two days after the symptoms onset (OR 3.2, 95% CI 1.6–6.4, p = 0.001). Obtained results confirmed that patients with chronic underlying illness/condition and older than 15 years had the highest risk for serious complications from influenza and highlighted the importance of start of antiviral therapy within the first two days of illness in order to reduce the risk for the most severe outcomes of influenza, such as acute respiratory distress syndrome and lethal outcome.