# 6354
Normally by the end of May influenza activity in the Northern Hemisphere has returned to summer background levels, and our focus turns to the Southern Hemisphere’s flu season.
Last week the May 24th edition of Hong Kong’s Flu Express indicated that influenza activity continues at unusually high levels for this time of year.
According to a Hong Kong Centre For Health Protection press release today, influenza activity continues to rise in their city, and a general caution has been issued.
29 May 2012
Influenza activity reaches highest level this year
The Centre for Health Protection (CHP) of the Department of Health today (May 29) called on the public to maintain vigilance against seasonal influenza as the latest surveillance data shows that local influenza activity is at its highest level this year.
The Public Health Laboratory Centre (PHLC) of the CHP has detected a further increase in the number of influenza detections. The weekly number of influenza detections at the PHLC increased from 329 in the week ending May 5 to 1,113 in the week ending May 26, the highest number recorded so far this year. The number of institutional influenza-like illness (ILI) outbreaks increased from 16 to 64 during the same period. The current circulating influenza virus strain is influenza A(H3N2) virus, accounting for more than 95 per cent of all the influenza detections in the past four weeks.
From January 13 to noon on May 28, there were 214 cases (including 128 deaths), with ICU admissions or deaths with laboratory-confirmed influenza recorded by the enhanced surveillance system set up by CHP with the Hospital Authority and private hospitals to monitor the severity of influenza activity during influenza peak seasons. Fourteen paediatric cases (including two deaths) with severe influenza-associated complications or deaths have been recorded this year (as of May 28). Compared with the winter flu season in the first quarter of 2011, the 2012 flu season has caused a higher proportion of serious/fatal cases among elderly people aged 65 years or above, and a lower proportion of serious/fatal cases among children aged below 5 years.
A spokesperson for the CHP said, "Influenza activity is expected to stay high for some weeks to come, and we will continue to see some serious/fatal cases among all age groups, especially the elderly."
According to last week’s Flu Express, the predominant flu strain (by far) was H3:
In week 20, the number of influenza viruses
detected in the Public Health Laboratory Centre was 852, including 827 influenza A (H3) viruses, 22
influenza B viruses, 2 influenza A(H1N1)2009
viruses and 1 influenza A virus (Figure 3).
Although the flu season across Europe and the Americas was late in starting, and short in duration, there were signs that the seasonal H3N2 virus circulating had drifted antigenically – prompting a change in the formulation of this fall’s flu vaccine.
It will be interesting to see if further analysis reveals any antigenic changes in the H3 virus circulating in Hong Kong, and how closely they match with the new vaccine strain (A/Victoria/361/2011 (H3N2)-like virus).
