South Africa’s influenza surveillance report – compiled on the 23rd June 2011
National Health Laboratory Service, National Institute for Communicable Diseases, South Africa
It is usually in June or July each year that the five temperate countries of the Southern Hemisphere (Argentina, Australia, Chile, New Zealand and South Africa) experience the start of their influenza season.
As mentioned in WHO’s recent global summary (June 17th) this year South Africa is the first to report increased influenza activity. The latest report (June 23rd) from the National Health Laboratory Service section of the South African National Institute for Communicable Diseases describes information from its three standard surveillance systems based on Influenza-like Illness (ILI) (the so-called Viral Watch), Severe Acute Respiratory Illness (SARI) surveillance, and private hospital consultations.
The reports from all three are similar in their virology. After around week 16 there was a steady increase in the number of influenza viruses isolated with influenza A(H1N1)2009 almost exclusively the type reported. There have been a few sporadic reports of A(H3N2) but its only in the last 4 weeks that any influenza type B viruses have begun to be reported. Among private hospital consultations, and up to week 19, the reports match the trends observed with SARI and ILI. Outpatient consultations with a pneumonia and influenza (P&I) diagnosis started to be reported above baseline level around week 18 with a trend similar to the SARI reported data with a two-week delay, and the curve steadily increasing up to week 24. The curve for hospitalizations stratified by type of virus isolated as part of inpatient P&I diagnoses shows that Respiratory Syncytial Viruses (RSV) started to be isolated at the beginning of 2011 (week 1), peaking at or around week 13, and still as of week 23 these continue to be reported. However, the number of influenza isolates started to increase at around week 17, and continued to increase steadily coinciding with the nearly baseline levels of RSV currently reported.
ECDC extensively covered last year the evolution of the 2010 influenza season in the Southern Hemisphere – the series of regular reports were published on its website as Global Influenza Epidemiology Overviews for Europe.
ECDC Comment (29th June 2011):
The pattern of influenza infection and disease in the five Southern Hemisphere temperate countries has been of particular interest for Europe since 2009 as what the South has been experiencing then tended to happen in Europe a few months later. This pattern occurred both during the pandemic, and last year when the winter of 2010 in the Southern Hemisphere was more similar to what was then seen in the European Winter of 2010-2011 (1).
However the relationship is not exact and there was considerable diversity across the five countries in their 2010 winter (1). Equally though the experience of North America was different from the South and from Europe with A(H3N2) dominating as the A viruses in Canada and the United States when the pandemic A(H1N1)2009 viruses were the dominant viruses in Europe.
The viral mix in South Africa at the beginning of the 2010 season was different from what is seen now. Then A(H3N2) predominated initially rather than the pandemic A(H1N1) 2009 viruses (2). Last year influenza B was the most common influenza type reported as SARI cases with fewer presence of A(H3N2) viruses, with overall B viruses predominating and an almost absence of 2009 pandemic virus reports until late in the season after the World Cup (June 11th to July 11th) brought visitors to South Africa (3). ECDC will report further on the Southern Hemisphere trends as the season develops.
- ECDC Forward Look Risk Assessment 2010 October 2010
- ECDC Global Epidemiology with special focus on the interest in the Southern Hemisphere Temperate Zone 16 Jul 2010
- National Institute for Communicable Diseases Influenza surveillance report – South Africa Report compiled on 19 October 2010