March 28, 2017
2 min read

CDC: Incidence of influenza-like illnesses, deaths remain elevated in US

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Despite a decrease in influenza activity in the United States, the number of outpatient visits and deaths attributed to pneumonia and influenza remain high, according to a recent report prepared by CDC’s Influenza Division.

The report included data on influenza activity in the United States from Oct. 1 to March 18. According to the data, 92,505 of the 647,455 respiratory specimens tested in clinical laboratories and 31,673 of 65,061 respiratory specimens tested in public health laboratories were positive for influenza. Among them, 79.6% in clinical laboratories and 86.9% in public health laboratories were influenza A viruses. The most common influenza virus subtype reported by public health laboratories was influenza A(H3).

Researchers antigenically characterized 547 influenza A(H3N2) viruses, 176 influenza A(H1N1)pdm09 viruses and 346 influenza B viruses collected since Oct. 1. They found that 97.8% of influenza A(H3N2) viruses, 92.2% of influenza B/Victoria-lineage viruses, and all the influenza A(H1N1)pdm09 and influenza B/Yamagata-lineage viruses were similar to components of this season’s Northern Hemisphere vaccine recommendations. Susceptibility testing for antiviral medications, including Tamiflu (oseltamivir, Roche), Relenza (zanamivir, GlaxoSmithKline) and Rapivab (peramivir, BioCryst Pharmaceuticals) showed that all viruses tested were sensitive to all three antivirals.

The CDC reported that 3.2% of outpatient visits from March 12 to March 18 were due to influenza-like illnesses (ILI), which is above the national baseline of 2.2%. Regions experiencing the most ILI activity included Alabama, Georgia, Indiana, Kansas, Kentucky, Louisiana, Maryland, Minnesota, Mississippi, Oklahoma, South Carolina and Virginia.

The Influenza Hospitalization Surveillance Network, which collects data from 13 states, detected 14,103 laboratory-confirmed influenza-associated hospitalizations since Oct. 1. The overall hospitalization rate was 50.4 per 100,000 population, and was highest among adults aged 65 years and older (228.6 per 100,000 population). Based on available information, most hospitalizations were associated with influenza A viruses (88.3%). Among viruses with subtype information, 98% were A(H3N2).

Credit: CDC
Source: CDC

Additional data from the National Center for Health Statistics showed that 7.8% of deaths occurring the week ending March 4, 2017 were attributed to pneumonia and influenza, which is above the epidemic threshold of 7.5% for this week. Overall this season, 55 influenza-associated deaths have occurred in children.

Also in the report, the CDC listed WHO’s recommendations for the 2017-2018 Northern Hemisphere influenza vaccine composition. The organization recommends that trivalent vaccines contain an A/Michigan/45/2015 (H1N1)pdm09-like virus, an A/Hong Kong/4801/2014 (H3N2)-like virus, and a B/Brisbane/60/2008-like (B/Victoria lineage) virus. For quadrivalent vaccines, which have two influenza B viruses, WHO recommends including viruses in the trivalent vaccines as well as a B/Phuket/3073/2013-like (B/Yamagata lineage) virus.

“This is the same recommendation made for the 2017 Southern Hemisphere vaccines, but it does represent an update to the influenza A(H1N1) component recommended for 2016-2017 Northern Hemisphere influenza vaccines,” the report said. “These vaccine recommendations were based on several factors, including global influenza virologic and epidemiologic surveillance, genetic characterization, antigenic characterization, antiviral resistance, and the candidate vaccine viruses that are available for production.” – by Stephanie Viguers


CDC. Weekly U.S. Influenza Surveillance Report. 2017. Accessed March 28, 2017.