Influenza activity remains fairly low for this time of year, but has increased slightly in recent weeks. Interestingly, a flu season that early on appeared destined to be dominated by H3N2 has - in the past month - switched over to seeing a majority of H1N1 cases.
Today's FluView also carries a report on the 7th novel swine variant flu infection of the year.
First a quick look at the regular flu stats, then a look at the novel flu detection.
2015-2016 Influenza Season Week 52 ending January 2, 2016
All data are preliminary and may change as more reports are received.
Synopsis:During week 52 (December 26, 2015-January 2, 2016), influenza activity increased slightly in the United States.
- Viral Surveillance: The most frequently identified influenza virus type reported by public health laboratories during week 52 was influenza A, with influenza A (H1N1)pdm09 viruses predominating. The percentage of respiratory specimens testing positive for influenza in clinical laboratories was low.
- Novel Influenza A Virus: One human infection with a novel influenza A virus was reported.
- 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: Two influenza-associated pediatric deaths were reported.
- Outpatient Illness Surveillance: The proportion of outpatient visits for influenza-like illness (ILI) was 2.8%, which is above the national baseline of 2.1%. Seven of 10 regions reported ILI at or above region-specific baseline levels. Puerto Rico and two states experienced high ILI activity; New York City and two states experienced moderate ILI activity; seven states experienced low ILI activity; 39 states experienced minimal ILI activity; and the District of Columbia had insufficient data.
- Geographic Spread of Influenza: The geographic spread of influenza in Guam and two states were reported as widespread; six states reported regional activity; 13 states reported local activity; the U.S. Virgin Islands and 27 states reported sporadic activity; the District of Columbia and two states reported no influenza activity; and Puerto Rico did not report.
(Continue . . . )
While only rarely reported – partly due to limited surveillance and testing – swine variant influenza infections are suspected to be more common than we know (see CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012).
Illness due to these strains is usually mild to moderate, and the symptoms look like any other flu.
Up until about six years ago the CDC only received 1 or 2 swine variant infection reports each year. In 2010, that number jumped to 8, and in 2011 to 12. In 2012 we saw more than 300 cases – mostly mild - and nearly all associated with exposure to pigs at state and local agricultural fairs.
In 2015 we've received word of 7 cases (4 - H1N1v & 3 - H3N2v). Today's FluView has the details on this latest detection, which comes from New Jersey.
One human infection with a novel influenza A virus was reported by the state of New Jersey. The person was infected with an influenza A (H3N2) variant (H3N2v) virus. The patient was not hospitalized and has fully recovered from their illness. The patient visited a farm near where swine are frequently housed but no direct contact with swine was reported in the week prior to illness onset. No ongoing human-to-human transmission has been identified.
Early identification and investigation of human infections with novel influenza A viruses are critical so that the risk of infection can be more fully appreciated and appropriate public health measures can be taken. Additional information on influenza in swine, variant influenza infection in humans, and strategies to interact safely with swine can be found at http://www.cdc.gov/flu/swineflu/index.htm.While we’ve not seen sustained or efficient spread of these swine variant viruses in humans - like all flu viruses - swine variant viruses are capable of evolving, reassorting, and adapting to their hosts. Last summer we looked at a study that examine two recently discovered swine variant strains (see J. Virol: Novel Reassortant Human-like H3N2 & H3N1 Influenza A Viruses In Pigs).
They described both of these novel subtypes as “. . . virulent and can sustain onward transmission in pigs, and the naturally occurring mutations in the HA were associated with antigenic divergence from H3 IAV from human and swine’” and goes on to warn that ``. . . the potential risk of these emerging swine IAV to humans should be considered”.
Although avian flu gets most of the headlines – mostly due to their high fatality rate – swine flu viruses are considered more likely to jump to humans, simply because they fall in the same H1, H2, and H3 subtypes as `humanized’ flu strains of the past 130 years.
The 2009 H1N1 pandemic virus evolved in pigs, and so easily could the next pandemic virus.
For some more recent blogs on swine and swine variant influenza, you may wish to revisit:
PNAS: The Pandemic Potential Of Eurasian Avian-like H1N1 (EAH1N1) Swine Influenza
Eurosurveillance: Seroprevalence Of Cross-Reactive Antibodies To Swine H3N2v – Germany
JID: Evolutionary Dynamics Of Influenza A Viruses In US Exhibition Swine