Mix and match: A new swine flu virus is lurking among us

The CDC and the Infectious Diseases Society of America released cautionary statements about a new swine influenza virus that has been increasingly detected in a few inland states. The virus is a type A (H3N2) that contains the genetic footprint of a conventional influenza A virus, along with markers for H3 and most notably the M gene from the infamous 2009 influenza A (H1N1) pandemic virus. This happens because influenza virus, an orthomyxovirus, has a single stranded, negative RNA genome split into eight separate segments. Think of it as eight chromosomes. Infect a pig with an avian and human flu, shake it well and voilà: We are talking pandemic now.

Of the 153 infections reported from July 12 to Aug. 9, 93% occurred in children aged younger than 18 years and detected in Indiana, Ohio, Hawaii and Illinois. All had direct or indirect exposure to swine.

As for testing, we learned from the H1N1 pandemic not to trust the rapid antigen detection assays due to sensitivities ranging in the 40% to 60% range. The presence of the so called H3N2v — the v for variant — can only be confirmed by the CDC’s Flu rRT-PCR Dx Panel assay. Interestingly, the CDC tested seven H3N2v viruses with seven different and commonly used FDA-cleared rapid kits. Only four detected all seven H3N2v viruses. If you want to know which ones, take a look at the Table.

Bottom line: If this thing continues to spread, we will have to rely on new and special polymerase chain reactions one more time. If patients present with flu-like symptoms, ask the patients and families about direct or indirect exposure to pigs in the week preceding the symptoms.

As a side note, I vividly remember when I was in med school and intrigued with the pandemic flu tale I came across with a review paper by none other than Dr. Paul Glezen. It was a 1996 article titled “Emerging infections: pandemic influenza” (Epidemiol Rev. 1996;18(1):64-76). The statement that stuck into my mind was that “swine are considered the most likely ‘mixing vessel’” [for gene reassortment]. He then went on about the pitfalls on calculating excess mortality attributed to influenza that I still have to read after a coffee fix to sink it in. Dr. Glezen is so passionate when he talks about influenza. If it wasn’t because it sounds odd, one would say that he “lives and breathes influenza.”

As for what clinicians need to do — the CDC states that a person with a positive result of a molecular assay on respiratory specimens for influenza A, or positive results for influenza A and for H3 (A+, H3+) or influenza A nonsubtypeable (A+, H1-, H3-) in a patient with an epidemiological link to swine exposure should be considered a probable H3N2v case.

Specimens from probable H3N2v cases (with exposure to swine) should be forwarded to the state health department laboratory for additional testing.

A nasopharyngeal swab or aspirate (or a combined nasal swab and throat swab) should be sent into viral transport medium and the state or local health department should be contacted to arrange transport. A timely diagnosis should be requested at a state public health laboratory.

Flu is an old and all-modern disease. Emerging and re-emerging. It carries a promise for change. And, so far, it has delivered.