Last week, in the wake of two Ohio County Fairs reporting outbreaks of Swine H3N2, the CDC reported 11 mild cases of swine variant H3N2v influenza out of Ohio. This week the CDC's week 30 FluView adds one more case, but with the twist that this week's case is H1N2v.
Reports of human infection with novel swine variant influenza (H1N1v, H1N2v & H3N2v) are fairly rare, due to their (often) unremarkable presentation and limited laboratory testing, but they likely occur more often than we know.
The H3N2v strain is by far the most common, making up 94% of all reported cases (n=384) in the United States over the past 11 years. H1N1v comes in 2nd, with 20 cases (4%).
H1N2v has beenthe least common, with just 9 cases reported up until today (the last reported was last November CDC FluView Week 46: 1 Novel H1N2v Infection In Iowa). Today's report - the third in a little over a year - brings that total to 10.
First the FluView report, then I'll return with a bit more.
Since the influenza subtypes that commonly circulate in swine (H1, H2, and H3) are also the same that have caused all of the human pandemics going back 130 years (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?), they are generally regarded as having less far to `jump’ to humans than do many avian viruses.
Novel Influenza A Virus:One additional human infection with a novel influenza A virus was detected in Ohio during week 30. The person was infected with an influenza A (H1N2) variant (H1N2v) virus and reported direct exposure to swine in a fair setting during the week preceding illness onset.
This patient was younger than 18 years of age, was not hospitalized, and has fully recovered from their illness. No human-to-human transmission of this virus has been identified. Public health and agriculture officials are investigating the extent of disease among humans and swine, but no increases in influenza-like illness in the community have been reported. This is the first human infection with an H1N2v virus identified in 2017.
Early identification and investigation of human infections with novel influenza A viruses are critical to ensure timely risk assessment and so that 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.
The 2009 H1N1 pandemic was caused by a swine variant H1N1 virus that had kicked around swine herds for a decade or more before it adapted well enough to humans to transmit easily in the community.
The CDC maintains a comprehensive Swine/Variant Influenza page where you'll find the latest case counts, safety and prevention information, and guidance for health care providers.
And for a more thorough review of studies on swine variant viruses, you may wish to revisit my blog from early last month: