Flu activity remains below epidemic threshold

CDC. MMWR. 2012;61(7):123-128.a>

Issue: March 2012

Influenza activity has remained low for the 2011-2012 influenza season, with a slight increase in the first week of February, according to Lisa Grohskopf, MD, MPH, who presented data during this week’s Advisory Committee on Immunization Practices meeting.

Grohskopf, associate chief for policy and liaison activities for the CDC’s Epidemiology and Prevention Branch, Influenza Division, told committee members that influenza A has predominated this season, accounting for 90% of the more than 78,000 respiratory specimens tested. Of the influenza A viruses that were subtyped, 84% were influenza A (H3N2), but influenza A (H1N1)pdm09 and influenza B viruses have been detected.

For the week ending Feb. 11, the geographic spread of influenza was considered sporadic, with the exception of California, which had widespread influenza activity. The CDC received the first report of widespread US activity the week of Feb. 4.

“These numbers differ significantly from last year’s numbers for the same time, because last year many states reported widespread activity,” Grohskopf said. “This season has gotten off to a slow start because influenza typically peaks in February.”

Influenza-like illness remains below epidemic threshold, and since Oct. 2, the weekly percentage of deaths attributed to pneumonia and influenza has not exceeded the epidemic threshold for more than 1 week of this season, according to Grohskopf.

She also said just three pediatric deaths have been reported to the CDC during this influenza season. This number differs significantly from the 122 pediatric deaths reported during the 2010-2011 influenza season.

“It is stunning to me the lack of childhood deaths this year,” said ACIP member Jonathan Temte, MD, PhD, professor of family medicine at the University of Wisconsin School of Medicine and Public Health.

Despite the good news, CDC officials warned that influenza morbidity and mortality could still peak.

“We could still have a virulent influenza season, but it may be getting a late start,” said Melinda Wharton, MD, MPH, deputy director, National Center for Immunization and Respiratory Diseases.

“We hope we will continue to have little flu activity, but we should continue to vaccinate, just in case,” said Joseph Bresee, MD, chief of the Epidemiology and Prevention Branch of the CDC’s Influenza Division.

Moving from prevention to treatment, Tim Uyeki, MD, MPH, of the CDC’s Influenza Division, said 100% of the viral specimens tested since October have been sensitive to both oseltamivir (Tamiflu, Roche) and zanamivir (Relenza, GlaxoSmithKline), and patients should be treated as early as possible if influenza is suspected.

“Start treatment immediately,” Uyeki said. “Don’t wait for results of testing to begin treatment with these antivirals.”

Because of continued high levels of resistance to adamantanes among the circulating influenza viruses, amantadine and rimantadine should not be used, according to the CDC. – by Cassandra A. Richards

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