All data are preliminary and may change as more reports are received. Synopsis: Influenza activity in the United States increased slightly. 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 since September 30, 2018. Below is a summary of the key influenza indicators for the week ending December 1, 2018: • Viral Surveillance: Influenza A viruses have predominated in the United States since the beginning of October. The percentage of respiratory specimens testing positive for influenza in clinical laboratories remains low, but is increasing. 
 ◦ 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. 
 ◦ Antiviral Resistance: All viruses tested show susceptibility to the neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir). 
 • Influenza-like Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) remained at 2.2%, which is at the national baseline of 2.2%. Four of 10 regions reported ILI at or above their region-specific baseline level. 
 ◦ ILI State Activity Indictor Map: Two states experienced high ILI activity; two states experienced moderate ILI activity; New York City and eight states experienced low ILI activity; and the District of Columbia, Puerto Rico, and 38 states experienced minimal ILI activity. 
 • Geographic Spread of Influenza: The geographic spread of influenza in one state was reported as widespread; nine states reported regional activity; 18 states reported local activity; the District of Columbia, Puerto Rico, the U.S. Virgin Islands and 22 states reported sporadic activity; and Guam did not report. 
 • Influenza-associated Hospitalizations A cumulative rate of 1.3 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported. 
 • 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: No influenza-associated pediatric deaths were reported to CDC for week 48. 


Stephen B. Thacker CDC Library collection