Influenza season takes hold across the nation

Data collected by the Centers for Disease Control and Prevention (CDC) indicate widespread geographic influenza activity in 41 states for the agency's most recent reporting period, Dec. 23-29, 2012. The proportion of outpatient visits for influenza-like illness (ILI) was 5.6 percent, according to CDC, above the national baseline of 2.2 percent.

CDC said the increase in ILI activity for the most recent period "may be attributed in part to a reduced number of routine healthcare visits during the [holidays], which has been observed in previous seasons." The agency defines ILI as fever (temperature of 100°F or greater) and cough and/or sore throat.

Nine of 10 CDC reporting regions said ILI was above region-specific baseline levels. Overall, 29 states and New York City experienced high ILI activity, and another nine states experienced moderate ILI activity. Two influenza-associated pediatric deaths were reported, both associated with influenza B viruses.

Of the 9,363 specimens tested and reported by laboratories collaborating with the U.S. World Health Organization and National Respiratory and Enteric Virus Surveillance System, about 32 percent were positive for influenza.

Pulpit rock

Graphic credit: CDC

Region 5, which encompasses Illinois, Indiana, Michigan, Minnesota, Ohio and Wisconsin, reported about 58 percent of specimens tested positive for influenza over the most recent three weeks, with all six of the area's jurisdictions indicating regional or widespread activity. Region 1 (Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont) reported about 45 percent of specimens positive, followed by Region 3 (Delaware, District of Columbia, Maryland, Pennsylvania, Virginia and West Virginia) at about 43 percent.

Only Region 9 (Arizona, California, Guam, Hawaii and Nevada) reported normal ILI activity.

Since the start of the flu season, according to CDC, influenza A (H3N2) viruses have predominated nationally, followed by influenza B viruses, while 2009 H1N1 viruses have been identified rarely.

No new human infections with novel influenza A viruses were reported to CDC during the week of Dec. 23-29. A total of 312 infections with variant influenza viruses (308 H3N2v viruses, 3 H1N2v viruses, and 1 H1N1v virus) have been reported from 11 states since July 2012.

CDC said that between Oct. 1, 2012 and Dec. 29, 2012, 2,257 laboratory-confirmed influenza-associated hospitalizations were reported, a rate of 8.1 per 100,000 population. Among all hospitalizations, 1,924 (about 85 percent) were associated with influenza A and 312 (about 14 percent) with influenza B. There was no virus type information for 19 hospitalizations (about 1 percent). Among hospitalizations with influenza A subtype information, 475 (about 98 percent) were attributed to H3 and 9 (about 2 percent) were attributed to 2009 H1N1.

CDC-provided information about vaccination, infection control, prevention, treatment and diagnosis of seasonal influenza can be accessed here.