Determining the provincial and national burden of influenza-associated severe acute respiratory illness in South Africa using a rapid assessment methodology

Local disease burden data are necessary to set national influenza vaccination policy. In 2010 the population of South Africa was 50 million and the HIV prevalence was 11%. We used a previously developed methodology to determine severe influenza burden in South Africa. Hospitalized severe acute respiratory illness (SARI) incidence was calculated, stratified by HIV status, for four age groups using data from population-based surveillance in one site situated in Gauteng Province for 2009–2011. These rates were adjusted for each of the remaining 8 provinces based on their prevalence of risk factors for pneumonia and healthcare- seeking behavior. We estimated non-hospitalized influenza-associated SARI from healthcare utilization surveys at two sites and used the percent of SARI cases positive for influenza from sentinel surveillance to derive the influenza-associated SARI rate. We applied rates of hospitalized and non-hospitalized influenza-associated SARI to census data to calculate the national number of cases. The percent of SARI cases that tested positive for influenza ranged from 7–17% depending on age group, year, province and HIV status. In 2010, there were an estimated 21,555 total severe influenza cases in HIV-uninfected individuals and 13,876 in HIV-infected individuals. In 2011, there were an estimated 29,892 total severe influenza cases in HIV-uninfected individuals and 17,289 in HIV-infected individuals. The incidence of influenza-associated SARI was highest in children <5 years and was higher in HIV-infected than HIV-uninfected persons in all age groups. Influenza virus was associated with a substantial amount of severe disease, especially in young children and HIV-infected populations in South Africa.S1 Table. Provincial adjustment factors for severe acute respiratory illness (SARI) healthcare- seeking behavior, 2009–2011.S2 Table. Estimated hospitalized severe acute respiratory illness (SARI) incidence (95% C. I.) stratified by HIV serostatus for South Africa, 2009–2011. Data are rates per 100,000 persons.S3 Table. Influenza-associated hospitalized severe acute respiratory illness (SARI) incidence and number of cases in each province for 2009–2011, stratified by HIV serostatus.S1 Appendix. Equations used in calculation of annual number of cases of influenza-associated severe acute respiratory illness (SARI).The Global Health Research Graduate Student Award, Centre for Global Health, Johns Hopkins Bloomberg School of Public Health: http://www.hopkinsglobalhealth.org/.http://www.plosone.orgam201