title: Risk factors associated with hospitalisation for influenza-associated severe acute respiratory illness in South Africa: A case-population study.
abstract: Influenza 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.
  
  
  
  We 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.
  
  
  
  From 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) 3.5-4.16], HIV infection (CPR 3.61, 95% CI 3.5-3.71), asthma (CPR 2.45, 95% CI 2.19-2.73), previous history of hospital admission in the past 12months (CPR 2.07, 95% CI 1.92-2.23), and tuberculosis (CPR 1.85, 95% CI 1.68-2.02). When stratified by age, there is increased risk of hospitalisation in those ⩽5yearsof age (CPR 3.07, 95% CI 2.93-3.21) and among those 35yearsof age and above (CPR 1.23, 95% CI 1.28-1.18). Male sex (CPR 0.85, 95% CI 0.82-0.88) and completion of pneumococcal conjugate vaccination schedule in children <5yearsof age (CPR 0.74, 95% CI 0.71-0.77) were associated with decreased risk of hospitalisation.
  
  
  
  These results identify groups at high-risk for severe influenza who should be considered potential targets for influenza vaccination in South Africa and similar settings.
authors.affiliation: Nuffield Department of Population Health, University of Oxford, Oxford, England. Electronic address: abadomtochukwu@gmail.com.
authors.forename: Tochukwu Raphael
authors.initials: TR
authors.lastname: Abadom
authors.affiliation: Nuffield Department of Population Health, University of Oxford, Oxford, England. Electronic address: adrian.smith@dph.ox.ac.uk.
authors.forename: Adrian D
authors.initials: AD
authors.lastname: Smith
authors.affiliation: Influenza Program, Centers for Disease Control and Prevention, Pretoria, South Africa; Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, USA. Electronic address: stefanot@nicd.ac.za.
authors.forename: Stefano
authors.initials: S
authors.lastname: Tempia
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa. Electronic address: ShabirM@nicd.ac.za.
authors.forename: Shabir A
authors.initials: SA
authors.lastname: Madhi
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa. Electronic address: cherylc@nicd.ac.za.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Cohen
authors.affiliation: Influenza Program, Centers for Disease Control and Prevention, Pretoria, South Africa; Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, USA; U.S. Public Health Service, Rockville, MD, USA; Expanded Programme on Immunization, Department of Immunization, Vaccines and Biologicals, World Health Organization, Geneva, Switzerland(1). Electronic address: cohena@who.int.
authors.forename: Adam L
authors.initials: AL
authors.lastname: Cohen
mesh_terms: D000208:Acute Disease / Q000453:epidemiology; D000293:Adolescent; D000328:Adult; D000368:Aged; D001249:Asthma / Q000150:complications / Q000453:epidemiology; D002648:Child; D005260:Female; D015658:HIV Infections / Q000150:complications / Q000453:epidemiology; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage; D007251:Influenza, Human / Q000150:complications / Q000453:epidemiology* / Q000517:prevention & control* / Q000821:virology; D008297:Male; D008875:Middle Aged; D022242:Pneumococcal Vaccines / Q000008:administration & dosage; D011159:Population Surveillance; D011203:Poverty / Q000706:statistics & numerical data; D015995:Prevalence; D012141:Respiratory Tract Infections / Q000453:epidemiology* / Q000821:virology; D012307:Risk Factors; D018571:Sentinel Surveillance; D012737:Sex Factors; D013019:South Africa / Q000453:epidemiology; D014376:Tuberculosis / Q000150:complications / Q000453:epidemiology; D014611:Vaccination / Q000706:statistics & numerical data; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines; D022242:Pneumococcal Vaccines
keywords: Hospitalisation; Influenza; Risk factors; Vaccine