North America's late arriving and unusually mild flu season is essentially over, but in the southern hemisphere influenza activity continues to ramp up - particularly in parts of Central and South America.
In the tropics flu is pretty much a year-round low-level threat, although it often surges during the rainy season.
While we've seen reports (see An Early Start To South America's Flu Season?) of increased flu activity in parts of South America, so far we've seen no indication of anything other than that an early, and active, H1N1 season has arrived.
Today's report from the WHO - current as of the end of May - seems to bear that out.
13 June 2016, - Update number 265, based on data up to 29 May, 2016
Influenza activity in the temperate zone of the northern hemisphere continued to decrease to inter-seasonal levels. In temperate countries in the southern hemisphere, influenza activity started to increase in South America and South Africa, but remained low overall in most of Oceania.
- In North America, influenza activity continued to decrease with influenza B virus accounting for the majority of influenza detections. Influenza-like illness (ILI) levels were below seasonal thresholds.
- Influenza activity continued to decrease in Europe and temperate Asia with a predominance of influenza B virus activity.
- In the northern temperate and central tropical regions of Africa, influenza activity was generally low with influenza A virus detections reported in Western Africa and influenza A and B virus detections reported in Eastern Africa.
- In Central America and the Caribbean countries, influenza and other respiratory virus activities remained generally low. El Salvador and Panama however reported increased influenza activity with influenza A(H1N1)pdm09 virus.
- In tropical South America, influenza activity generally decreased or remained low except in Bolivia where influenza A(H1N1)pdm09 activity increased. Colombia and Peru reported increased respiratory syncytial virus (RSV) detections. Acute respiratory infections (ARI) and severe acute respiratory infections (SARI) remained elevated in Colombia and ARI and pneumonia levels increased in children in Peru.
- In tropical countries of South Asia, influenza activity was generally low with increased influenza B virus in some countries.
- The influenza season began in temperate South America, with ILI and SARI activities increased above seasonal thresholds in Argentina, Chile and Paraguay. Respiratory virus detections were still low but increasing, with influenza A(H1N1)pdm09 predominant among influenza detections.
- In the temperate countries of Southern Africa, the influenza season began with increasing influenza activity due to predominantly influenza B viruses.
- In Oceania, influenza virus activity remained low. Some islands in the Pacific reported increased ILI activity.
- National Influenza Centres (NICs) and other national influenza laboratories from 84 countries, areas or territories reported data to FluNet for the time period from 16 May 2016 to 29 May 2016 (data as of 2016-06-10 03:53:24 UTC). The WHO GISRS laboratories tested more than 61285 specimens during that time period. 4320 were positive for influenza viruses, of which 1276 (29.5%) were typed as influenza A and 3044 (70.5%) as influenza B. Of the sub-typed influenza A viruses, 540 (71%) were influenza A(H1N1)pdm09 and 221 (29%) were influenza A(H3N2). Of the characterized B viruses, 221 (30.4%) belonged to the B-Yamagata lineage and 505 (69.6%) to the B-Victoria lineage.