BACKGROUND : Studies describing the epidemiology of influenza B lineages in South Africa are lacking. METHODS : We conducted a prospective study to describe the circulation of influenza B/Victoria and B/
Yamagata lineages among patients of all ages enrolled in South Africa through three respiratory
illness surveillance systems between 2005 and 2014: (i) the Viral Watch (VW) program
enrolled outpatients with influenza-like illness (ILI) from private healthcare facilities
during 2005±2014; (ii) the influenza-like illnesses program enrolled outpatients in public
healthcare clinics (ILI/PHC) during 2012±2014; and (iii) the severe acute respiratory illnesses
(SARI) program enrolled inpatients from public hospitals during 2009±2014. Influenza
B viruses were detected by virus isolation during 2005 to 2009 and by real-time
reverse transcription polymerase chain reaction from 2009±2014. Clinical and epidemiological
characteristics of patients hospitalized with SARI and infected with different influenza B
lineages were also compared using unconditional logistic regression.
RESULTS : Influenza viruses were detected in 22% (8,706/39,804) of specimens from patients with ILI
or SARI during 2005±2014, of which 24% (2,087) were positive for influenza B. Influenza B
viruses predominated in all three surveillance systems in 2010. B/Victoria predominated prior to 2011 (except 2008) whereas B/Yamagata predominated thereafter (except 2012). B
lineages co-circulated in all seasons, except in 2013 and 2014 for SARI and ILI/PHC surveillance.
Among influenza B-positive SARI cases, the detection of influenza B/Yamagata compared
to influenza B/Victoria was significantly higher in individuals aged 45±64 years
(adjusted odds ratio [aOR]: 4.2; 95% confidence interval [CI]: 1.1±16.5) and 65 years
(aOR: 12.2; 95% CI: 2.3±64.4) compared to children aged 0±4 years, but was significantly
lower in HIV-infected patients (aOR: 0.4; 95% CI: 0.2±0.9).
CONCLUSION : B lineages co-circulated in most seasons except in 2013 and 2014. Hospitalized SARI
cases display differential susceptibility for the two influenza B lineages, with B/Victoria being
more prevalent among children and HIV-infected persons.