Influenza activity continues to increase in the United States and most of the country is now experiencing high levels of influenza-like-illness (ILI), according to the Centers for Disease Control and Prevention (CDC)'s latest FluView report.
• Viral Surveillance: 31.6 percent were positive for influenza. (up from 29.6 reported last week)
• Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and
influenza (P&I) was below the epidemic threshold.
• Influenza-Associated Pediatric Deaths: Two influenza-associated pediatric deaths were
reported and were associated with influenza B viruses. (Total of 18)
• Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 5.6 percent; above the national baseline of 2.2 percent and up again from last week. New York City and 29 states experienced high ILI activity (up from 16 states last week)
• Geographic Spread of Influenza: Forty-one states reported widespread geographic
influenza activity (up from 31 last week)
According to the CDC, the proportion of people seeing their healthcare provider with ILI in the United States has been elevated for four consecutive weeks, climbing sharply from 2.8 percent to 5.6 percent during that time. Last season, which was relatively mild, ILI peaked at 2.2 percent. Comparatively, during 1998-1999 and 2003-2004, which were moderately severe seasons, ILI peaked at 7.6 percent. During 2007-2008, another moderately severe season, ILI peaked at 6.0 percent. During the 2009 H1N1 pandemic, ILI peaked at 7.7 percent.
During the past 10 influenza seasons, ILI remained at or above baseline for an average of 12 consecutive weeks, with a range of one week (2011-2012 season) to 16 weeks (2005-2006 season). During the pandemic, the proportion of visits to doctors for ILI remained above the national baseline for 19 consecutive weeks.
“Reports of influenza-like-illness (ILI) are nearing what have been peak levels during moderately severe seasons,” according to Dr. Joe Bresee, chief of the Epidemiology and Prevention Branch in CDC’s Influenza Division. CDC continues to recommend influenza vaccination and antiviral treatment when appropriate at this time.
“While we can’t say for certain how severe this season will be, we can say that a lot of people are getting sick with influenza and we are getting reports of severe illness and hospitalizations,” says Bresee.
“Anyone who has not already been vaccinated should do so now,” Bresee adds. “And it’s important to remember that people who have severe influenza illness, or who are at high risk of serious influenza-related complications, should get treated with influenza antiviral medications if they get flu symptoms regardless of whether or not they got vaccinated. Also, you don’t need to wait for a positive laboratory test to start taking antivirals.”
Information about flu-related hospitalizations is collected from 15 states to calculate a rate of laboratory-confirmed influenza-associated hospitalizations. Right now, cumulative influenza hospitalization rates are 8.1 per 100,000 people. According to Bresee, “This is high for this time of year.”
Influenza-associated pediatric deaths have been reportable to CDC since the 2004-2005 season. To date, CDC has received reports of 18 pediatric deaths this season.
One factor that may indicate increased severity this season is that the predominant circulating type of influenza virus is influenza A (H3N2) viruses, which account for about 76 percent of the viruses reported. Bresee explains “typically ‘H3N2 seasons’ have been more severe, with higher numbers of hospitalizations and deaths, but we will have to see how the season plays out.”
So far this season, most (91 percent) of the influenza viruses that have been analyzed at CDC are like the viruses included in the 2012-2013 influenza vaccine. The match between the vaccine virus and circulating viruses is one factor that impacts how well the vaccine works. But Bresee cautions that other factors are involved.
“While influenza vaccination offers the best protection we have against influenza, it's still possible that some people may become ill despite being vaccinated,” says Bresee. “Healthcare providers and the public should remember that influenza antiviral medications are a second line of defense against influenza.”
CDC continues to recommend influenza vaccination and antiviral treatment when appropriate at this time.
CDC has recommendations on the use of antiviral medications (sold commercially as “Tamiflu®” and “Relenza®”) to treat influenza illness. Antiviral treatment, started as early as possible after becoming ill, is recommended for any patients with confirmed or suspected influenza who are hospitalized, seriously ill, or ill and at high risk of serious influenza-related complications, including young children, people 65 and older, people with certain underlying medical conditions and pregnant women. Treatment should begin as soon as influenza is suspected, regardless of vaccination status or rapid test results and should not be delayed for confirmatory testing.