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 20 (May 13-19, 2018), influenza activity continued to decrease 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: One influenza-associated pediatric death was reported. • Influenza-associated Hospitalizations: A cumulative rate of 106.6 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 1.2%, which is below the national baseline of 2.2%. All 10 regions reported ILI below region-specific baseline levels. New York City, the District of Columbia, Puerto Rico and all 50 states experienced minimal ILI activity. • Geographic Spread of Influenza: The geographic spread of influenza in one state was reported as widespread; Guam, Puerto Rico and one state reported regional activity; seven states reported local activity; the District of Columbia, the U.S. Virgin Islands and 37 states reported sporadic activity; and four states reported no influenza activity.

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