CDC sees mixed flu picture, remaining threat for seniors

Jan 25, 2013 (CIDRAP News) – Deaths from pneumonia and flu in the United States rose sharply last week, with a rise in hospitalizations that continues to hit older people the hardest, though other disease indicators showed declines, the US Centers for Disease Control and Prevention (CDC) reported today.

The severity levels aren't unexpected for a season in which the H3N2 virus dominates, and the later rise in deaths and hospitalizations is a fairly typical pattern, the CDC added.

Two markers that rose early are beginning to drop off. The proportion of clinic visits for flu fell to 4.3% from 4.6% over the previous week, though the level is still above the national baseline of 2.2%. Likewise, the percentage of respiratory swabs testing positive for flu dropped from an adjusted level of 32.5% to 26.1%.

The CDC said though flu seems to be leveling off in some areas such as the South, the Southeast, New England, and the Midwest, activity increased in other parts of the country, including the Southwest and the Northwest.

Last week 47 states reported widespread geographic flu activity, down from 48 the week before.

The CDC called the rise in pneumonia and flu deaths from 8.4% to 9.8% considerable and pointed out that the level was above the epidemic threshold for the third week in a row.

Lyn Finelli, DrPH, who leads surveillance and outbreak response team in the CDC's influenza division, said in a flu news update that last week's percentage of pneumonia and flu deaths is the highest the CDC has seen in nearly a decade, but it's comparable to past severe flu seasons. For example, she said the level reached 10% during the 2003-04 season and 11.2% during the 1999-2000 season.

She said the CDC is closely watching the hospitalization rate, especially for seniors, because over the first half of January the level for that age-group has risen steeply, from 50 hospitalizations per 100,000 people to almost 98 hospitalizations, surpassing the previously highest rate for seniors of 73.7, which occurred during the 2007-08 flu season.

However, Finelli cautioned that the CDC has been collecting the hospitalization rates for seniors only since 2007. "So it's difficult to make the same kind of historical comparisons that we can for mortality," she said.

"The overall picture is clear. This season is severe for seniors, who are being hit hardest in terms of serious illnesses and deaths. It's really important that these people seek care and get treated promptly," Finelli said.

The CDC alluded to its concerns about hospitalizations and deaths this year among seniors in an influenza update for geriatricians and other clinicians. It reminded health providers that older people are at greater risk of flu complications in general, especially when H3N2 is the predominant strain.

Although this season's developments haven't changed the CDC's recommendations, it urged clinicians to continue offering flu vaccine and to consider empiric antiviral treatment for all patients older than 65 with suspected flu, regardless of severity.

Meanwhile, 8 more pediatric flu deaths were reported to the CDC last week, raising the season's total to 37. Two were from unsubtyped influenza A infections that occurred in early January, and the other 6 deaths were linked to influenza B, of which 5 occurred earlier in the flu season.

Testing of seasonal flu strains for resistance to neuraminidase inhibitors identified the flu season's first oseltamivir-resistant sample, which was a 2009 H1N1 virus.

Canada and Mexico
Elsewhere in North America, flu activity in Canada increased for the week ending Jan 13, with the percentage of doctors' visits for flulike illness running above the expected baseline for this time of year, according to a regional flu update yesterday from the Pan American Health Organization (PAHO). The agency said that 15 regions among the provinces of British Columbia, Alberta, Ontario, Quebec, and Newfoundland reported widespread flu activity.

H3N2 is the dominant strain in Canada, but influenza B accounts for a smaller portion of cases than in the United States, according to PAHO.

Mexican flu indicators showed declining activity with no recent 2009 H1N1 detections and influenza B as the dominant strain, followed by H3N2, the group said.

Mixed indicators in Europe
The flu picture for Europe showed mixed signals, according to an influenza update today from the European Centre for Disease Prevention and Control (ECDC). Seventeen countries reported increasing transmission, while Denmark, Ireland, the Netherlands, Norway, and the United Kingdom reported decreasing trends.

Though the H3N2 virus is circulating in Europe, the 2009 H1N1 strain has been detected in increasing proportions, according to the ECDC. In contrast, the former pandemic virus has been responsible for only a small percentage of flu infections in the United States.

The ECDC's analysis of all-cause mortality found no overall increase this season so far, but three countries—Denmark, Scotland, and England—reported mortality increases in seniors. The agency noted that the increase was especially clear in Denmark, where the H3N2 dominates and flu activity peaked around Christmas.

See also:

Jan 25 CDC weekly flu surveillance report

Jan 25 CDC flu news and spotlight report

Jan 23 CDC influenza update for geriatricians and other clinicians

Jan 24 PAHO regional flu update

Jan 25 ECDC weekly flu surveillance update

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