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 17 (April 22-28, 2018), influenza activity decreased in the United States. • Viral Surveillance: Overall, influenza A(H3) viruses have predominated this season. Since early March, influenza B viruses have been more frequently reported than influenza A viruses. 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 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. • Influenza-associated Hospitalizations: A cumulative rate of 106.0 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 1.5%, which is below the national baseline of 2.2%. One of 10 regions reported ILI at or above their region-specific baseline level. Two states experienced low ILI activity; and New York City, the District of Columbia, Puerto Rico, and 48 states experienced minimal ILI activity. • Geographic Spread of Influenza: The geographic spread of influenza in three states was reported as widespread; Guam, Puerto Rico and seven states reported regional activity; 24 states reported local activity; the District of Columbia, and 14 states reported sporadic activity; and the U.S. Virgin Islands and two states reported no influenza activity.

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