Dec 30, 2010 (CIDRAP News) – The winter flu season is now officially under way in the Northern Hemisphere, the World Health Organization (WHO) reported today in releasing its most recent influenza data.
Meanwhile, US data also released today show influenza activity again rising, and a third report says flu activity is increasing dramatically in the United Kingdom.
The WHO update says cases of influenza-like illness (ILI) are now above baseline in parts of Canada and the United States and are primarily associated with influenza A (H3N2) and influenza B.
The United Kingdom is seeing a surge in mild and severe cases for the last 3 weeks, according to the WHO, primarily associated with pandemic 2009 H1N1 and, to a lesser extent, influenza B. The illness pattern among those with H1N1 is similar to that seen during the pandemic last year, primarily affecting young adults, especially those with underlying conditions.
Elsewhere in Europe, the Middle East, and north Asia, ILI rates are low, but recent increases have been reported in some regions, the WHO report added.
Tropical regions are seeing little activity, but Sri Lanka has reported a "marked increase" of pandemic 2009 H1N1 cases, including 22 deaths.
CDC surveillance data
The US Centers for Disease Control and Prevention (CDC) said that for the week ending Dec 25 influenza activity continues to increase, with the proportion of deaths attributed to pneumonia and influenza reaching the epidemic threshold.
Most recent surveillance data show that flu is widespread in five states: Alabama, Georgia, Mississippi, New York, and Virginia. Puerto Rico and 13 states reported regional activity; 9 states are experiencing local activity; 23 states, the District of Columbia, and the US Virgin Islands reported sporadic activity; and Guam has seen no flu activity.
The proportion of outpatient visits for ILI was 2.7%, which is above the national baseline of 2.5%.
Of the 3,284 US respiratory specimens tested, 689 (21.0%) were positive for influenza; specimens from the southeast had the highest rate, with 23.4% testing positive for flu.
Of the 689 specimens that were found positive for flu, 479 (69.5%) were influenza A, and 210 (30.5%) were influenza B. Of the 202 influenza A samples that were subtyped, only 15 (7.4%) were pandemic 2009 H1N1, while 187 (92.6%) were H3 subtypes, presumably H3N2, which can cause more severe disease.
One influenza-related death in a child was reported and was associated with the H3 strain. There were no reports of antiviral-resistant strains, and the subtypes identified to be circulating in the community matched the three strains in the vaccine well.
UK weekly report
In the United Kingdom, ILI consultation rates in general practitioners' (GPs') offices are now above baseline levels in all four countries (England, Northern Ireland, Scotland, and Wales), according to data released today by the country's Health Protection Agency (HPA).
However, pandemic 2009 H1N1 and influenza B are the predominant strains, with only a few cases of H3N2 reported. UK strains are also well matched to the vaccine.
In the past week, England's ILI consultation rate to GP offices for England rose 43%, from 87.1 to 124.4 per 100,000. The rates per 100,000 for Scotland, Wales, and Northern Ireland were 58.4, 92.1, and 99.4, respectively.
One hundred and twenty-six of 189 (66.7%) specimens from patients with ILI presenting to sentinel GPs in England for the week ending Dec 26 tested positive for influenza. Over the last 4 months 39 flu-related UK deaths have been confirmed, the majority in people who were not vaccinated.
As of 2 weeks ago, 68.5% of those in England over 65 years old had received the flu vaccine. For those in a high-risk group and age 65 or under, it was 43.0%.
Dec 30 WHO report
CDC weekly flu update
CDC flu activity map
Dec 30 HPA update