Nov 30, 2012 (CIDRAP News) – Flu activity in the United States rose substantially last week, hitting the national baseline at the earliest point in the season since the 2003-04 flu season, and the first case of variant H3N2 (H3N2v) since September has been reported from Iowa, the US Centers for Disease Control and Prevention (CDC) reported today.
The big rise in flu activity comes just days before the CDC and their state and local public health partners launch a week-long event to encourage the public to get vaccinated against the flu. CDC experts have always maintained that flu activity is unpredictable and that patterns can quickly change.
Much of the rise in flu activity is from south central and southeastern states, the CDC said, noting that five of its regions are reporting flulike illness activity above their baselines. However, it is seeing wide variation in the regional percentages of respiratory samples testing positive for flu, ranging from 3.8% to 20.6%.
Nationally, the percentage of respiratory specimens testing positive for flu last week was 15.2%, the CDC reported. The percentage of doctor visits for flulike illness climbed to the national baseline of 2.2%, an increase from the 1.6% reported the previous week.
The percentage of deaths from pneumonia and flu was 6.3% last week, putting it below the epidemic threshold of 6.7%. No new pediatric flu deaths were reported, holding the total so far this season to two.
Four states reported widespread geographic spread of flu: Alaska, Mississippi, New York, and South Carolina. Seven reported regional spread, and 19 states reported local activity, an increase from the eight reported the previous week.
The CDC said all three seasonal flu strains are circulating, with H3N2 responsible for about 35% of the subtyped influenza viruses. Of 140 viruses the CDC has antigenically characterized, both of the two 2009 H1N1 viruses circulating match the component in the 2012-13 vaccine, as do all 90 of the H3N2 viruses circulating. Of 48 influenza B samples tested, 34 (70.8%) matched the Yamagata lineage virus included in this season's vaccine.
Elsewhere, European health officials are seeing little evidence of sustained flu transmission, though the proportion of respiratory samples testing positive for flu increased slightly over the past week, according to an update today from the European Centre for Disease Prevention and Control (ECDC). Malta was the only country that reported local geographic spread, and 12 countries reported only sporadic spread.
In the United States, National Influenza Vaccination Week runs from Dec 2 through 8, and the CDC has posted several resources to help state and local health officials remind the public to get vaccinated against the flu. The CDC will host a media teleconference on Dec 3 to provide an update on the flu season and share the latest vaccination coverage data.
Variant H3N2
The CDC also said it received a new report of H3N2v infection, the first to be reported since the end of September. The patient, from Iowa, had no contact with swine or other livestock the week before becoming sick.
Patricia Quinlisk, MD, MPH, medical director of the Iowa Department of Public Health, told CIDRAP News that the H3N2v infection was detected within the past 2 weeks through routine surveillance. The patient is a child who has since recovered. Iowa reported three H3N2v cases in 2011, but it did not detect any over the summer and fall when several states—especially Indiana and Ohio—were reporting cases linked to fairs and other similar events.
Health officials are investigating the source of the infection. Quinlisk said another member of the child's family had been sick previously but was not tested.
The CDC said the new H3N2v case pushes the number of such infections reported since July to 311. Most cases were related to contact with swine in fair settings. The CDC said though instances of human-to-human transmission have been identified, there is no evidence of ongoing transmission.
See also:
Nov 30 CDC flu situation update
Nov 30 CDC flu surveillance update
Nov 30 ECDC influenza update
CDC National Influenza Vaccination Week materials
