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

During week 9 (February 26-March 4, 2017), influenza activity decreased, but remained elevated in the United States.

• Viral Surveillance: The most frequently identified influenza virus subtype reported by public health laboratories during week 9 was influenza A (H3). The percentage of respiratory specimens testing positive for influenza in clinical laboratories decreased.

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

• Influenza-associated Pediatric Deaths: Eight influenza-associated pediatric deaths were reported.

• Influenza-associated Hospitalizations: A cumulative rate for the season of 43.5 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported.

• Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 3.6%, which is above the national baseline of 2.2%. Eight of ten regions reported ILI at or above their region-specific baseline levels. 14 states experienced high ILI activity; 12 states experienced moderate ILI activity; eight states experienced low ILI activity; New York City, Puerto Rico, and 16 states experienced minimal ILI activity; and the District of Columbia had insufficient data.

• Geographic Spread of Influenza: The geographic spread of influenza in Puerto Rico and 39 states was reported as widespread; Guam and eight states reported regional activity; the District of Columbia and two states reported local activity; one state reported sporadic activity; and the U.S. Virgin Islands reported no activity.

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Stephen B. Thacker CDC Library collection

United States