Monday, December 28, 2015

FluView Week 50: Influenza Activity Low But Increasing


Due to the holidays the CDC released their weekly FluView update today instead of last Friday, and while flu activity remains low across the nation, there are signs it is increasing. 

The one constant with seasonal flu, however, is you never know what kind of flu season you are going to get. And that goes for the timing, the dominant strain, and the severity.

Some years flu arrives in the fall, other years it peaks in late winter or early spring.  As shown below for 2011-12 - sometimes it barely arrives at all.  Although that is far from the norm.

Today's FluView indicates - for the second week running - that H1N1 is now the most common flu strain reported, although the number of isolates tested remains low. 

Up until early December, H3N2 was leading the pack.  

H3N2 dominant flu seasons tend to be more severe, particularly among the elderly, while H1N1 tends to hit younger adults harder.  Given the low number of viruses identified, it is too soon to be certain of how this will play out.

Here is a brief summary from today's report:

2015-2016 Influenza Season Week 50 ending December 19, 2015

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


During week 50 (December 13-19, 2015), influenza activity increased slightly in the United States.
  • Viral Surveillance: The most frequently identified influenza virus type reported by public health laboratories during week 50 was influenza A, with influenza A (H1N1)pdm09 viruses predominating. The percentage of respiratory specimens testing positive for influenza in clinical laboratories was low.
  • Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was below their system-specific epidemic threshold in both the NCHS Mortality Surveillance System and the 122 Cities Mortality Reporting System.
  • Influenza-associated Pediatric Deaths: One influenza-associated pediatric death was reported.
  • Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 2.2%, which is above the national baseline of 2.1%. Four of 10 regions reported ILI at or above region-specific baseline levels. One state experienced high ILI activity; Puerto Rico and two states experienced moderate ILI activity; New York City and three states experienced low ILI activity; 44 states experienced minimal ILI activity; and the District of Columbia had insufficient data.
  • Geographic Spread of Influenza: The geographic spread of influenza in Guam, Puerto Rico, and five states was reported as regional; the U.S. Virgin Islands and 14 states reported local activity; the District of Columbia and 27 states reported sporadic activity; and four states reported no influenza activity.