xTAG®

2009 Influenza A/H1N1 (“swine flu”, or 2009 H1N1 influenza) is a newly emerging sub-type of the H1N1 influenza A virus. This strain is of particular concern because it can cause severe disease and fatalities, even among young, otherwise healthy people who would not be considered vulnerable to serious infection from seasonal influenza strains.

The symptoms of 2009 Influenza A/H1N1 are usually similar to those of normal flu, although in some cases gastrointestinal symptoms (e.g., vomiting, diarrhea) that are not typical of seasonal influenza have been reported. If a patient has these symptoms, the likelihood of exposure to the 2009 Influenza A/H1N1 strain should be taken into account and further diagnostic tests performed, in order to classify the case as suspected, probable, or confirmed. A suspected case is one in which influenza-like symptoms are confirmed and the patient had suspected exposure within seven days of illness onset. A probable case is a suspected case where rapid or molecular tests show a positive result for influenza A and follow-up with molecular tests indicates that the virus does not carry the seasonal version of the H1 or H3 antigen. A confirmed case is one that is verified by local public health authorities.

The commonly used rapid tests for influenza A cannot distinguish 2009 Influenza A/H1N1 from normal seasonal influenza A strains. In contrast, xTAG RVP can be used as an aid in the detection of 2009 Influenza A/H1N1 (swine flu).  The xTAG panel tests for the influenza A matrix gene shared by all subtypes, including swine flu.  It also includes specific probes for the seasonal strains of H1 and H3.  As a result, there are 3 types of positive Flu A results generated by the test:

1) Flu A positive – unsubtypeable
2) Flu A positive – seasonal H1
3) Flu A positive – seasonal H3

Extensive empirical testing carried out during the spring 2009 swine flu outbreak has shown that 99% of swine flu specimens generate a “Flu A positive – unsubtypeable” result¹.

Prompt and reliable diagnosis of 2009 Influenza A/H1N1 is central to limiting the spread of infection and making treatment decisions. Two antiviral medications – oseltamivir and zanamivir – have been shown to be effective both as treatment for 2009 Influenza A/H1N1 infection and as prophylaxis against infection in individuals at high risk of contracting the virus. Seasonal influenza vaccines do not protect against 2009 Influenza A/H1N1; vaccines against 2009 Influenza A/H1N1 influenza are currently in development.

Reference:
1. Likelihood that an unsubtypeable influenza A virus result obtained with the Luminex xTAG respiratory virus panel is indicative of infection with novel A/H1N1 (swine like) influenza virus. Ginocchio et al., JCM 2009 Jul;47(7):2347-8. Epub 2009 Jun 3.

2. US xTAG RVP Package Insert.