Influenza widespread across 25 states

ATLANTA — The Centers for Disease Control and Prevention on Friday updated the nation’s influenza status. Nine states are reporting high influenza-like activity (a metric that captures the severity of a flu outbreak) and 25 states are reporting widespread activity (a metric that captures the estimated level of spread of influenza activity through state and territorial epidemiologists reports.)

Indiana, Maryland, Mississippi, North Carolina, Texas and Virginia joined Alabama, Louisiana and Oklahoma, while Georgia dropped to moderate ILI activity in the last week. However, ILI activity is widespread across the South and stretching up through the East Coast, according to CDC data.

The CDC noted that the ILI activity level reported within a state captures the severity of a flu outbreak by measuring the number of outpatient visits for ILI. That metric does not measure the extent of geographic spread of ILI within a state, however, which means a high number of ILI reported in a single city could skew the data for the entire state.

The CDC is reporting geographic spread of influenza — a metric that captures the estimated level of spread of influenza activity through state and territorial epidemiologists reports — in addition to its severity report.

Of all influenza A viruses tested since Oct. 30, 2010, 23.9% were identified as the 2009 H1N1 virus, up from 15.8% the week prior. As many as 42% of the specimens were identified as an H3N2 virus, similar to the H3N2 component of the 2010-11 triumvirate influenza vaccine.

The proportion of outpatient visits for ILI was 3.6% — above the national baseline of 2.5%. Last week, the proportion of outpatient visits was 2.9%.