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

Synopsis: During week 11 (March 13-19, 2016), influenza activity decreased slightly, but remained elevated in the United States.

• Viral Surveillance: The most frequently identified influenza virus type reported by public health laboratories during week 11 was influenza A, with influenza A (H1N1)pdm09 viruses predominating. 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 NCHS Mortality Surveillance System and above the system-specific epidemic threshold in the 122 Cities Mortality Reporting System.

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

• Influenza-associated Hospitalizations: A cumulative rate for the season of 18.2 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 3.2%, which is above the national baseline of 2.1%. All 10 regions reported ILI at or above region-specific baseline levels. Puerto Rico and seven states experienced high ILI activity; New York City and eight states experienced moderate ILI activity; 20 states experienced low ILI activity; 15 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 10 states reported regional activity; the District of Columbia and one state reported local activity; and the U.S. Virgin Islands did not report.

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United States

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