Synopsis: During week 51 (December 15-21, 2013), influenza activity continued to increase in the United States.

o Viral Surveillance:Of 6,813 specimens tested and reported by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories during week 51, 1,639 (24.1%) were positive for influenza.

o Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was below the epidemic threshold.

o Influenza–associated Pediatric Deaths: One influenza-associated pediatric death that occurred during the 2012-2013 season was reported.

o Influenza–associated Hospitalizations :A cumulative rate for the season of 4.3 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported.

o Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 3.0%, above the national baseline of 2.0%. Eight regions reported ILI at or above region-specific baseline levels. Six states experienced high ILI activity; eight states experienced moderate ILI activity; six states experienced low ILI activity; 28 states experienced minimal ILI activity, and the District of Columbia, New York City, and two states had insufficient data.

o Geographic Spread of Influenza : The geographic spread of influenza in 10 states was reported as widespread; Guam and 23 states reported regional influenza activity; 12 states reported local influenza activity; the District of Columbia, Puerto Rico, and four states reported sporadic influenza activity, and the U.S. Virgin Islands and one state did not report.

Stephen B. Thacker CDC Library collection

United States