All data are preliminary and may change as more reports are received.

Synopsis: Influenza activity in the United States remains low, although small increases in activity were reported. Influenza A(H1N1)pdm09, influenza A(H3N2), and influenza B viruses continue to co-circulate, with influenza A(H1N1)pdm09 viruses reported most commonly by public health laboratories during the most recent three weeks. Below is a summary of the key influenza indicators for the week ending October 27, 2018:

• Viral Surveillance: Influenza A viruses have predominated in the United States since the beginning of July. The percentage of respiratory specimens testing positive for influenza in clinical laboratories was low.

o Virus Characterization: The majority of influenza viruses characterized antigenically and genetically are similar to the cell-grown reference viruses representing the 2018–2019 Northern Hemisphere influenza vaccine viruses.

o Antiviral Resistance: All viruses tested since late May show susceptibility to the antiviral drugs oseltamivir, zanamivir, and peramivir.

• Influenza-like Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) increased slightly to 1.7%, which is below the national baseline of 2.2%. All regions reported ILI below their region-specific baseline level.

• ILI State Activity Indictor Map: New York City and two states experienced low ILI activity; the District of Columbia and 48 states experienced minimal ILI activity; and Puerto Rico had insufficient data.

• Geographic Spread of Influenza: The geographic spread of influenza in five states was reported as local; the District of Columbia, Puerto Rico, the U.S. Virgin Islands and 43 states reported sporadic activity; two states reported no activity; and Guam did not report.

• Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was below the system-specific epidemic threshold in the National Center for Health Statistics (NCHS) Mortality Surveillance System.

• Influenza-associated Pediatric Deaths: Three influenza-associated pediatric deaths were reported to CDC. One occurred during the 2018-2019 season and two occurred during the 2017-2018 season.