The US flu season gained more steam last week, with most states reporting widespread activity and three more pediatric flu deaths, the US Centers for Disease Control and Prevention (CDC) said in its weekly update today.

Nationally, the percentage of clinic visits for flulike illness rose to 3.3%, up from 3.1% the week before, and all 10 of the CDC's regions are above their baselines for that indicator. The agency also noted three new flu-related deaths in children.

More states with high, widespread activity

The flulike illness surveillance map, which also tracks clinic visits for flu, shows that activity is high in 18 states, up from 9 in the previous week.

Geographically, flu is now widespread in 36 states, up from 30 the week before.

The percentage of respiratory samples testing positive for flu was up sharply, rising to 16.1% last week compared to 12.7% the previous week. The 2009 H1N1 strain is still dominant in most of the country, except for in the southeast where H3N2 has been more common.

At public health labs, there were few influenza B detections, with influenza A making up 98.4% of flu viruses. Of subtyped influenza A viruses, 81.2% were 2009 H1N1 and 18.8% were H3N2.

Antiviral susceptibility testing on a subset of viruses found two 2009 H1N1 viruses with highly reduced susceptibility to the antiviral drugs oseltamivir and peramivir, with two more with reduced susceptibility to oseltamivir.

Hospitalization, death levels rise

Regarding hospitalizations for flu, the overall rate rose to 14.8 per 100,000 population, up from 12.4 per 100,000 population the week before. The level, however, is still much lower than this time last season when the cumulative rate was 41.9 per 100,000 population.

The CDC said this season's hospitalization rates are highest in people ages 65 and older, followed by children younger than 4.

Of the three pediatric flu deaths reported to the CDC last week, two were related to 2009 H1N1 and one was due to an unsubtyped influenza A virus. The reports lift the season's number of pediatric flu deaths to 22.

Overall deaths from pneumonia and flu, an indicator that typically lags other markers, rose to 7.2% last week and are above the epidemic threshold, and in an accompanying situation report, the CDC said that indicator has now topped the epidemic level for 2 weeks this season.

See also:

Jan 25 CDC weekly FluView report

Jan 25 CDC flu situation report