Vaccine

BackgroundInfluenza is a common cause of severe respiratory illness, but risk factors for hospitalisation in low income settings with a high HIV prevalence are not well described. We aimed to assess risk factors associated with influenza-associated severe acute respiratory illness (SARI) hospitalisation in South Africa.MethodsWe conducted a case-population study using data on risk conditions in patients hospitalised with SARI and the national prevalence of these conditions. Data on hospitalised cases were from the national SARI surveillance program while data on the referent population were from the latest national census or health and demographic surveillance surveys.FindingsFrom 2009 to 2012, we identified 3646 (7.9%) of 46,031 enrolled cases of SARI that were associated with influenza infection. Risk factors associated with hospitalisation included previous history of smoking [case-population ratio (CPR) 3.82, 95% confidence interval (CI) 3.5\u20134.16], HIV infection (CPR 3.61, 95% CI 3.5\u20133.71), asthma (CPR 2.45, 95% CI 2.19\u20132.73), previous history of hospital admission in the past 12 months (CPR 2.07, 95% CI 1.92\u20132.23), and tuberculosis (CPR 1.85, 95% CI 1.68\u20132.02). When stratified by age, there is increased risk of hospitalisation in those 645 years of age (CPR 3.07, 95% CI 2.93\u20133.21) and among those 35 years of age and above (CPR 1.23, 95% CI 1.28\u20131.18). Male sex (CPR 0.85, 95% CI 0.82\u20130.88) and completion of pneumococcal conjugate vaccination schedule in children