Though some flu markers are starting to level off, activity is still high and will likely hang on for several more weeks, which would make this flu season last longer than average, the US Centers for Disease Control and Prevention (CDC) said today.
It also said the indicator for flu hospitalizations for seniors is the highest it has ever seen, topping the previous high set just a week earlier. This is in spite of the fact that overall hospitalizations appear to be starting to decline.
A typical flu season lasts about 13 weeks, but so far this season, which saw an early start, levels have been elevated for 12 weeks in a row, a sign that disease activity may persist longer than usual, the CDC said.
Elderly hit hard
Flu levels that fell slightly last week include the percentage of respiratory specimens that tested positive for flu, which dropped from 17.5% to 14.9% last week, and the percentage of clinic visits for influenza-like illness (ILI), which decreased slightly from 4.1% to 3.8%. All 10 of the CDC's regions are reporting that the percentage of clinic visits for flu is running above their seasonal baselines.
For flu hospitalizations, the overall cumulative rate was 44.1 per 100,000 population, up a bit from 43.5 per 100,000 population the week before with the rate of increase starting to slow, the CDC said.
The agency noted, however, that the rate for people age 65 and older climbed to 217.3 per 100,000, the highest hospitalization level the CDC has recorded since it first started collecting data on flu-linked hospitalization in adults during the 2005-06 season.
The previous week the rate in that age-group was 213.8 per 100,000. Prior to that, the previous high was 183.2 per 100,000, set in 2012-13, another year dominated by the H3N2 strain, which tends to cause more severe disease.
H3N2 mismatch continues
The CDC said H3N2 is still the most common strain detected, with few sample testing positive for influenza B and even fewer positive for the 2009 H1N1 virus. Of the H3N2 viruses tested, 68.6% did not match the H3N2 strain included in this year's vaccine.
Deaths from flu and pneumonia decreased slightly last week but are still well above the epidemic threshold. The CDC said it received reports of 11 pediatric flu deaths last week, increasing this season's total to 80. Four involved the H3N2 strain, 5 were related to unsubtyped influenza A, 1 was from influenza B, and 1 involved an influenza A and influenza B co-infection.
Flu was reported as widespread in 32 states and Puerto Rico, and ILI intensity, another marker based on clinic visits, was reported as high in 15 states and Puerto Rico. Those numbers are down from 40 and 29 states the week before, respectively. Areas reporting the highest flu levels last week are located in the south central and northeastern parts of the country.
Feb 13 CDC FluView report
Feb 13 CDC flu situation update