National Center for Immunization and Respiratory Diseases (U.S.). Influenza Division.

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

During week 4 (January 22-28, 2017), influenza activity increased in the United States.

• Viral Surveillance: The most frequently identified influenza virus subtype reported by public health laboratories during week 4 was influenza A (H3). The percentage of respiratory specimens testing positive for influenza in clinical laboratories increased.

• Pneumonia and Influenza Mortality: Due to data processing problems, the National Center for Health Statistics (NCHS) mortality surveillance data for the week ending January 14, 2015 (week 2) will not be published this week.

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

• Influenza-associated Hospitalizations: A cumulative rate for the season of 20.3 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 3.9%, which is above the national baseline of 2.2%. All 10 regions reported ILI at or above their region-specific baseline levels. New York City and 15 states experienced high ILI activity; Puerto Rico and 11 states experienced moderate ILI activity; 14 states experienced low ILI activity; 10 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 40 states was reported as widespread; Guam and nine states reported regional activity; the District of Columbia and one state reported local activity; and the U.S. Virgin Islands reported no activity.

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