Percentage of Visits for Influenza-like Illness (ILI) Reported by the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet), National Summary 2008-2009 and Previous Two Seasons

After rising precipitously earlier this year, the percentage of doctor visits nationwide that were related to flu-like symptoms dropped for a second week this week, according to data collected by the Outpatient Influenza-like Illness Surveillance Network (ILINet).

According to the CDC 2009 H1N1 Situation Update:

This is the second week of national decreases in ILI after four consecutive weeks of sharp increases. (All regions but one showed declines in ILI. Region I (CT, ME, MA, NH, RI and VT) continues to show sharp increases in ILI activity. While ILI declined overall nationally, visits to doctors for influenza-like illness remain higher than what is seen during the peak of many regular flu seasons.

Also from the CDC report:

• Total influenza hospitalization rates for laboratory-confirmed flu continue to climb and remain higher than expected for this time of year. Hospitalization rates continue to be highest in younger populations with the highest hospitalization rate reported in children 0-4 years old.
• The proportion of deaths attributed to pneumonia and influenza (P&I) based on the 122 Cities Report continues to increase and has been higher than what is expected for six weeks now. In addition, 35 flu-related pediatric deaths were reported this week: 26 of these deaths were associated with laboratory confirmed 2009 H1N1; eight were influenza A viruses, but were not subtyped; and one was an influenza B virus. Since April 2009, CDC has received reports of 156 laboratory-confirmed pediatric 2009 H1N1 deaths, one influenza B death, and another 23 pediatric deaths that were laboratory confirmed as influenza, but the flu virus subtype was not determined.
• Forty-six states are reporting widespread influenza activity at this time; a decline of two states over last week. They are: Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Montana, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, and Wyoming. This many reports of widespread activity at this time of year are unprecedented during seasonal flu.
• Almost all of the influenza viruses identified so far continue to be 2009 H1N1 influenza A viruses. These viruses remain similar to the virus chosen for the 2009 H1N1 vaccine, and remain susceptible to the antiviral drugs oseltamivir and zanamivir with rare exception

*All data are preliminary and may change as more reports are received.

Source: Center for Disease Control 2009 H1N1 Situation Update