US flu activity heating up

Flu activity in the United States showed a modest jump last week, with the percentage of clinic visits for flu-like illness rising above the national baseline for the first time this season, the US Centers for Disease Control and Prevention (CDC) said today.

For clinic visits, three regions of the country were above their baselines last week: those encompassing southeastern, south-central, and west-central states.

Another flu marker, the percentage of respiratory samples that tested positive for flu, also showed a clear increase last week, rising from 10.1% to 13.3%. The CDC said that level has been rising over the last 7 weeks.

The percentage of lab-confirmed flu hospitalizations rose from 1.2 per 100,000 population to 2.0 last week, and 88% were related to influenza A. Of the subtyped samples in those patients, 95.3% were the 2009 H1N1 virus and 4.1% involved the H3N2 strain.

Overall deaths from flu and pneumonia were below the seasonal baseline, and no pediatric flu deaths were reported last week to the CDC, keeping the seasonal total so far at three.

Four states reported high flu-like illness activity, up from just two the week before: Alabama, Louisiana, Mississippi, and Texas. Fourteen states reported regional geographic spread, up from six reported the previous week, according to the CDC>

Canada and Mexico report flu rises

Canada also saw a jump in flu activity last week, according to a report yesterday from the Public Health Agency of Canada (PHAC). The share of respiratory samples that were positive for influenza rose from 3.7% to 6.1%, though the country saw a drop in clinic visits for flu.

Influenza A accounted for 94% of the positive respiratory specimens, and of the subtyped isolates, most were the 2009 H1N1 strain. Lab testing of a subset of flu viruses found one more ostelamivir (Tamiflu)-resistant sample, raising the number of detections to seven so far. The CDC added that all of the samples showed sensitivity to zanamivir (Relenza), the other neuraminidase inhibitor.

As in the United States, the 2009 H1N1 virus is the dominant circulating strain, accounting for 83% of all influenza A specimens.

The PHAC said hospitalization levels from flu are increasing among both children and adults, with a majority of cases in both groups linked to the 2009 H1N1 virus. Two regions in Ontario and one in Quebec reported localized activity, and 23 regions across seven provinces reported sporadic activity.

South of the border, surveillance information from Mexico shows slight increasing trends for flu, according to a Dec 11 update from the Pan American Health Organization (PAHO). Of flu samples tested over the past few weeks, 76.7% were influenza A, of which nearly 61% were the 2009 H1N1 virus.

European flu levels remain low

In Europe, flu activity remained low, with no sign of sustained activity, though the percentage of sentinel specimens testing positive for flu has increased in some countries, the European Centre for Disease Prevention and Control (ECDC) said in an update today.

Unlike the United States and Canada, Europe is seeing a more even mix of influenza A viruses, which accounted for 82% of detections over the past 9 weeks. Of those, 55% were the 2009 H1N1 virus and 45% were the H3N2 strain.

Countries that reported increasing flu trends last week included Bulgaria, Lithuania, Poland, and Romania.

See also:

Dec 13 CDC FluView report

Dec 13 CDC flu situation update

Dec 13 ECDC weekly influenza report

Dec 12 PHAC FluWatch report

Dec 11 PAHO flu update

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