Flu is now widespread in five states, while activity continues to increase across the nation as a whole, said the US Centers for Disease Control and Prevention (CDC) in a weekly flu update on Thursday, when they also reported that the proportion of deaths attributed to pneumonia and influenza was now “at the epidemic threshold”.

In their update for week 51 of the United States 2010-2011 Influenza Season (covering week ending 25 December), the CDC said that 18 of the 54 jurisdictions under surveillance are now reporting regional or widespread activity.

For the week ending 25 December the CDC says:

  • Five states reported widespread flu activity (Alabama, Georgia, Mississippi, New York, and Virginia).
  • Puerto Rico and 13 states reported regional flu activity. The 13 states are: Arizona, Connecticut, Florida, Kentucky, Louisiana, Maine, Massachusetts, Nevada, New Jersey, Oklahoma, Pennsylvania, South Carolina, and Texas.
  • Nine states reported local flu activity (Illinois, Kansas, Minnesota, Montana, New Hampshire, New Mexico, North Carolina, Tennessee, and Washington).
  • Flu activity was reported by 23 other states, the District of Columbia, and the US Virgin Islands.
  • The only region not reporting any flu activity was Guam.

The federal agency said that 7.5% of all deaths reported through the 122-Cities Mortality Reporting System were due to pneumonia and influenza, which puts the nation at the “epidemic threshold of 7.5% for week 51”.

The CDC also said they received a report that one child in New York City died from an infection linked to flu type A (H3) in the week leading up to 11 December.

Overall in the 2010-2011 flu season, three influenza-associated pediatric deaths have been reported, two linked to type A (H3) and one linked to type A with no subtype determined.

In 50 states and Washington DC there are collaborating labs run by the World Health Organization (WHO) and the CDC’s own National Respiratory and Enteric Virus Surveillance System (NREVSS) that every week report the number of respiratory specimens tested for influenza and the number found positive by influenza type and subtype.

During week 51, these labs collected and tested 3,284 respiratory specimens, of which 689 (21 per cent) tested positive for flu virus.

Of the specimens that tested positive for flu virus, 69.5% (479 specimens) were type A and 30.5% (210 specimens) were type B.

Within the type A specimens, at least 3.1% (15 specimens) were positive for subtype 2009 H1N1, the so-called “swine flu” virus, 39% (187 specimens) were subtype H3, and 57.8% (277 specimens) were not tested for subtype.

The CDC said the proportion of outpatient visits for flu-like illnesses was 2.7% in the week leading up to 25 December: this figure is above the 2.5% national baseline.

Three states and New York City reported high levels of outpatient visits for flu-like illnesses, while six states reported moderate activity in this area. The rest of the country reported either low or minimal or insufficient data to show what the activity might be.

The CDC suggests that the increase in the percentage of outpatient visit may be partly due to reduction in routine healthcare visits during the holiday season. This has happened in previous years.

The agency stressed that their weekly update is based on preliminary data and the picture may change as more reports come in.

Source: CDC FluView (http://www.cdc.gov/flu/weekly/).

Written by: Catharine Paddock, PhD