CDC says flu is widespread in 49 states

[Guest Lisa Schnirring and Robert Roos]

Influenza activity was widespread in 49 US states by the end of last week, up from 44 states a week earlier, but the epidemic's growth was not as dramatic as it was the previous week, the Centers for Disease Control and Prevention (CDC) said today.

 

Nancy Cox, MD, chief of the CDC's influenza division, told reporters at a media teleconference today that Florida is the only state reporting only regional activity. "Flu activity has continued to increase, but not quite as dramatically as the increases we've seen over the previous 2 weeks," she said.

 

"From a 10-year perspective, we are within the normal parameters of what we'd expect for an influenza season," she said.

 

Cox said the predominant influenza subtype in the United States is still A/H3N2, though H1N1 subtypes were more common at the beginning of the season. Most of the H3N2 isolates the CDC has analyzed so far involve the A/Brisbane/10/2007-like variant, which does not match this season's vaccine. According to the most recent surveillance information, for the week ending Feb 16, 79% (55) of the H3N2 samples the CDC analyzed were the Brisbane variant.

 

Among the 69 influenza B samples the CDC has analyzed, 94% (64) were in the Yamagata lineage, which also is not included in this year's vaccine. In contrast, 88% (124 of 141) of H1N1 isolates analyzed so far matched the Solomon Islands strain used in the vaccine.

 

The number of pediatric deaths related to the flu rose to 22 last week, up 12 from the previous week's total, Cox reported.

 

Although only one of the three flu subtypes circulating this year is well matched by the vaccine, CDC officials say they haven't noted any unusual patterns of clinical consequences. Cox said the CDC often receives anecdotal reports of influenza in patients who have received the vaccine, even in years when the circulating viruses and the vaccine are well matched.

 

She said the CDC is conducting studies of the effectiveness of this year's vaccine and will publish the results in an upcoming issue of Morbidity and Mortality Weekly Report.

 

Physicians' impressions of flu season

Some physicians contacted by CIDRAP News this week stopped short of describing the flu season as worse than usual, despite the irregularities that have been reported with the vaccine and circulating strains.

 

William Schaffner, MD, chair of the Department of Preventive Medicine at the Vanderbilt University School of Medicine in Nashville, said flu has been increasing in Tennessee recently, but he expects the season to be no worse than average. Schaffner also is vice president of the National Foundation for Infectious Diseases.

 

"In the middle Tennessee area we're certainly seeing a lot of flu-like illness, and my sense is when the more specific diagnostic tests are being used, they're coming up positive," he said. "My sense is that we're going to have a moderate influenza season, not one that'll fill every bed in every hospital. But it's brisk—doctors and emergency rooms are getting lots of calls."

 

Noting that one flu strain in the vaccine (H1N1) matches well with viruses circulating in the United States, Schaffner said he was not worried about the imperfect match between the vaccine and viruses. "I'm not at all distressed that we have one bull's eye, one a little off the bull's eye, and one that misses the target completely. That's pretty good," he said.

 

"The major reason we give influenza vaccine is to prevent the complications of flu," Schaffner added. The vaccine may provide complete protection for young people with robust immune systems, he explained. In frail people, the vaccine often yields incomplete protection, but it may still prevent pneumonia, hospitalization, or worse, he said.

 

He added that mismatches between the vaccine and the viruses happen "with some frequency." Most of the time, "The issue is not whether there's a mismatch, but by how much. Analyses almost always indicate you have some protection."

 

Henry "Hank" Bernstein, DO, chief of general pediatrics at the Children's Hospital at Dartmouth, in Lebanon, N.H., said the flu season was quiet in his area until a few weeks ago. However, Bernstein, a member of the American Academy of Pediatrics' Committee on Infectious Diseases, said he has heard anecdotal reports from across the nation of vaccinated patients who were sick with flu.

 

"I emphasize that there are still vaccine doses available and that people should continue to get their immunizations until the spring," he said. "There are different peaks at different times throughout the season."

 

Priya Sampathkumar, MD, an infectious disease specialist at the Mayo Clinic in Rochester, Minn., said in an e-mail that she has seen influenza infections in vaccinated patients, but that the disease seems less severe in such instances.