FluView : Influenza Activity Continues To Decrease In Week 11

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While there are still some pockets of high ILI (influenza-like-illness) activity hanging on around the nation, for most of the country this year's flu season appears about over.

Outpatient visits for ILI have dropped rapidly (see below) the past few weeks and are now just above the national baseline level of 2.2%.

After a rough H3N2 season, for the first time this winter Influenza B has taken the lead, making up 57.5% of all influenza positive tests by the CDC in week 11.

While the full impact of this year's flu season won't be tallied for a couple of more months, the record number of hospitalizations (at least, since record keeping methods changed in 2010) will be a big part of it.

A brief summary from a much longer FluView Report follows:

2017-2018 Influenza Season Week 11 ending March 17, 2018

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

Synopsis:

During week 11 (March 11-17, 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 11, influenza B viruses were more frequently reported than influenza A viruses. 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 93.5 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 2.7%, which is above the national baseline of 2.2%. Nine of 10 regions reported ILI at or above region-specific baseline levels. Six states experienced high ILI activity; nine states experienced moderate ILI activity; New York City, Puerto Rico, the District of Columbia, and 17 states experienced low ILI activity; and 18 states experienced minimal ILI activity.
• Geographic Spread of Influenza: The geographic spread of influenza in 17 states was reported as widespread; Guam, Puerto Rico and 26 states reported regional activity; the District of Columbia and five states reported local activity; and the U.S. Virgin Islands and two states reported sporadic activity.

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While a flu-weary Northern Hemisphere is undoubtedly more than ready for a break, influenza never really stops, it just moves to another part of the world.

The odds of seeing a pandemic virus emerge in any given year is historically very low (around 3%), but studies suggest the most likely time for a pandemic to emerge is right after the end of the Northern Hemisphere flu season (PLoS Comp. Bio.: Spring & Early Summer Most Likely Time For A Pandemic).

So while our focus may gradually shift away from this year's flu season - between the upcoming Southern Hemisphere flu season, an array of emerging avian flu viruses, and a recent rise in swine variant flu reports - there should be plenty to keep track of over the summer.