Dec 21, 2012 (CIDRAP News) – Flu activity in the Northern Hemisphere continued to climb last week, led by a vigorous pace of infections in the United States and Canada in the lead-up to the Christmas holiday season, the World Health Organization (WHO) said today.
In its biweekly update, the WHO said flu activity in North America increased sharply compared with previous weeks, and while H3N2 is the dominant flu strain in both the United States and Canada, influenza B is playing a larger role in the US flu season so far than in Canada.
In Mexico the percentage of respiratory specimens testing positive for flu remained high at 25%, though the most common virus detected was influenza B, followed by H3N2, the WHO said.
In Europe, flu activity was low overall, but the pace of detections increased in a growing number of countries, the WHO said.
The Centers for Disease Control and Prevention (CDC) said today that most flu indicators continue to rise, with the highest activity levels in south central and southeastern states, though other parts of the country are also reporting increases. The number of states reporting widespread geographic spread rose to 29, compared with 18 the week before.
The proportion of doctor visits for flu-like illness was 3.2% last week, an increase from 2.8% the week before. The percentage of respiratory specimens testing positive for flu dropped slightly, to 28.3%.
CDC Director Tom Frieden, MD, MPH, said in a statement, "Today's report confirms that the U.S. flu season is off to an early start though it's too early to tell how severe our season might be." He said vaccination is the most important step for protecting against infection and that it's not too late to be immunized.
Deaths from pneumonia and flu were below the epidemic threshold. Two more pediatric flu deaths were reported, pushing the season's total to eight; one was linked to an unknown influenza A subtype and the other involved H3N2.
The WHO said the most recent report it received from Canada gave Ontario as the only region reporting widespread activity. Media reports yesterday and today noted that increased flu activity in Montreal and Alberta was pushing capacity at local emergency departments.
In Europe, the number of respiratory specimens testing positive for flu rose for the third straight week, reaching 17.2%, the European Centre for Disease Prevention and Control (ECDC) said in its weekly flu season update. Though many countries are still reporting stable flu trends, increasing activity was reported by nine countries: France, Germany, Hungary, Ireland, Luxembourg, Poland, Slovakia, Spain, and Wales.
Among viral isolates from both sentinel and nonsentinel sources in Europe last week, nearly 58% were influenza A, with about two-thirds of those the 2009 H1N1 virus.
Elsewhere, flu activity in northern Africa and the Eastern Mediterranean regions was low but increasing. In temperate areas of China flu activity remained low, with declining activity in tropical areas.
Flu activity also declined in Central America, the Caribbean, and tropical parts of South America, the WHO reported. Most of the activity was from the H3N2 virus, except in Cuba and Peru, where the 2009 H1N1 virus dominated.
Dec 21 CDC flu situation update
Dec 21 CDC weekly influenza update
Dec 21 statement from Tom Frieden
Dec 21 WHO global flu update
Dec 20 CTV Montreal report
Dec 21 Calgary Herald story
Dec 21 ECDC weekly influenza update