The influenza season, which started about a month earlier than usual, is picking up in intensity, according to the CDC's latest FluView report.
In the week ending Dec. 29, high flu-like illness activity was reported by 29 states and New York City, with moderate activity seen in another nine states. That compares with 16 states with high activity and eight with moderate activity the week before.
Overall, the percentage of outpatient visits for flu-like illness has exceeded the national baseline of 2.2% since the week ending Dec. 8, when it was 2.8%. In the most recent week, that figure was 5.6%, although the CDC noted that the increase could be at least partly attributed to fewer routine health visits during the holiday season.
"Reports of influenza-like-illness are nearing what have been peak levels during moderately severe seasons," Joe Bresee, MD, chief of the epidemiology and prevention branch of the CDC's influenza division, said in a statement.
In two other moderately severe seasons -- 1998-1999 and 2003-2004 -- the percentage of flu-related visits peaked at 7.6%. During the H1N1 pandemic in 2009, it reached as high as 7.7%.
It remains unclear how severe the current season will be, although the predominant circulating strain -- influenza A(H3N2) -- provides a clue. Historically, flu seasons dominated by that strain have resulted in higher numbers of deaths and hospitalizations.
So far this season, the proportion of deaths attributed to pneumonia and influenza (7%) remains just below the epidemic threshold of 7.1%. A total of 18 influenza-related pediatric deaths have been reported since the beginning of the season.
The influenza hospitalization rate is 8.1 per 100,000 people, which is "high for this time of year," according to Bresee. Most of the hospitalizations (85%) have been related to influenza A strains, and nearly of those were tied to A(H3N2).
The CDC continues to recommend annual influenza vaccination for everyone 6 months and older, and 91% of the viruses tested thus far have been similar to the strains found in the 2012-2013 seasonal vaccine.
As another line of defense, the CDC also has recommendations for the use of antivirals, including oseltamivir (Tamiflu) and zanamivir (Relenza).
"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 condition, and pregnant women," according to the agency.
"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."