Global & Disaster Medicine

CDC: influenza-like illness (ILI) activity is markedly down across the country this week, a clear sign that this year’s severe flu season continues to wind down.



During week 9 (February 25-March 3, 2018), influenza activity decreased in the United States.

  • Viral Surveillance: Overall, influenza A(H3) viruses have predominated this season. However, in recent weeks the proportion of influenza A viruses has declined, and during week 9, the numbers of influenza A and influenza B viruses reported were similar. 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 above the system-specific epidemic threshold in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
  • Influenza-associated Pediatric Deaths: Five influenza-associated pediatric deaths were reported.
  • Influenza-associated Hospitalizations: A cumulative rate of 86.3 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 3.7%, which is above the national baseline of 2.2%. All 10 regions reported ILI at or above region-specific baseline levels. New York City and 21 states experienced high ILI activity; 15 states experienced moderate ILI activity; the District of Columbia, Puerto Rico, and five states experienced low ILI activity; and nine states experienced minimal ILI activity.
  • Geographic Spread of Influenza:The geographic spread of influenza in Puerto Rico and 34 states was reported as widespread; Guam and 12 states reported regional activity; the District of Columbia and four states reported local activity; and the U.S. Virgin Islands reported no activity.

INFLUENZA Virus Isolated

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national levels of ILI and ARI


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