Update: Influenza Activity - United States, October 1, 2017-February 3, 2018

Abstract

Influenza activity in the United States began to increase in early November 2017 and rose sharply from December through February 3, 2018; elevated influenza activity is expected to continue for several more weeks. Influenza A viruses have been most commonly identified, with influenza A(H3N2) viruses predominating, but influenza A(H1N1)pdm09 and influenza B viruses were also reported. This report summarizes U.S. influenza activity* during October 1, 2017-February 3, 2018,^† and updates the previous summary (1).

FIGURE 1

Number and percentage of respiratory specimens testing positive for influenza reported by clinical laboratories, by influenza virus type and surveillance week — United States, October 1, 2017–February 3, 2018 * A total of 124,316 (18.7%) of 666,493 specimens tested were positive during October 1, 2017–February 3, 2018. ^† As of February 9, 2018.

FIGURE 2

Number of respiratory specimens testing positive for influenza reported by public health laboratories, by influenza virus type, subtype/lineage, and surveillance week — United States, October 1, 2017–February 3, 2018 * N = 27,669. ^† As of February 9, 2018.

FIGURE 3

Genetic characterization of U.S. viruses collected during October 1, 2017–February 3, 2018 Abbreviation: HA = hemagglutinin. * As of February 9, 2018.

FIGURE 4

Percentage of outpatient visits for influenza-like illness (ILI) reported to CDC, by surveillance week — U.S. Outpatient Influenza-Like Illness Surveillance Network (ILINet), 2017–18 influenza season and selected previous influenza seasons * Defined as fever (temperature of ≥100°F [≥37.8°C], oral or equivalent) and cough or sore throat, without a known cause other than influenza. As of February 9, 2018.