During week 16 (April 15-21, 2012), influenza activity was elevated in some areas of the United States, but declined nationally and in most regions.
U.S. Virologic Surveillance: Of the 2,987 specimens tested by U.S. World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories and reported to CDC/Influenza Division, 662 (22.2%) were positive for influenza.
Pneumonia and Influenza (P&I) Mortality Surveillance: The proportion of deaths attributed to P&I was below the epidemic threshold.
Influenza-associated Pediatric Mortality: Three influenza-associated pediatric deaths were reported. One was associated with a 2009 H1N1 virus, one was associated with a seasonal influenza A (H3) virus, and one was associated with an influenza A virus for which the subtype was not determined.
Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 1.3%, which is below the national baseline of 2.4%. Region 10 reported ILI above its region-specific baseline level. Four states experienced low ILI activity; New York City and 46 states experienced minimal ILI activity, and the District of Columbia had insufficient data to calculate ILI activity.
Geographic Spread of Influenza: Four states reported widespread geographic activity; 10 states reported regional influenza activity; 14 states reported local activity; the District of Columbia and 21 states reported sporadic activity; Guam, the U.S. Virgin Islands, and one state reported no influenza activity, and Puerto Rico did not report.