Flu-like symptoms? Inquire about swine exposure

December 1, 2011

With 10 cases this year of swine-origin influenza reported, mostly in children, the CDC is urging pediatricians to screen patients presenting with fever and respiratory symptoms for contact with swine. It also said you shouldn’t rely on commercially available diagnostic tests to tell the difference between swine flu and seasonal influenza A viruses. Here’s why.

With the discovery of 3 cases in Iowa of swine-origin triple reassortant influenza A (H3N2)
(S-OtrH3N2) in children, the National Centers for Disease Control and Prevention (CDC) is urging pediatricians to question whether patients presenting with fever and respiratory symptoms have had any contact with swine.

If the response leads you to suspect swine flu, CDC recommends that you treat with oseltamivir when indicated and also get a nasopharyngeal swab to a state public health laboratory for testing.

Even though swine exposure was not associated with the 3 most recent cases, CDC is advising that course of action because most previous cases of human infection with
S-OtrH3N2 viruses have been associated with swine exposure. The agency cautions that commercially available diagnostic tests, including point-of-care rapid tests, can detect infection with the S-OtrH3N2 virus but not differentiate it from seasonal influenza A viruses.

In the Iowa cases, all the children recovered without hospitalization. While the 3 children had been in contact with each other, none reported exposure to pigs or hogs. Viruses from the 3 patients were found to be resistant to amantadine and rimantadine but are expected to be susceptible to the neuraminidase inhibitor drugs oseltamivir and zanamivir based on their genetic sequence.

Since 2009, CDC has identified 18 human infections with swine-origin influenza A (H3N2) viruses. The most recent 10 cases, all occurring this year, were identified as infections with
S-OtrH3N2 viruses containing the matrix (M) gene from the pandemic 2009 influenza A (H1N1) virus (pH1N1). Those were reported in 4 states-Pennsylvania, Maine, Indiana, and Iowa.

CDC reported in a recent Morbidity and Mortality Weekly Report (MMWR) dispatch that these viruses are considered reassortant viruses between a swine-origin influenza A (H3N2) virus circulating in North American swine and a pH1N1 virus. It cautioned that while the 2011-2012 seasonal influenza vaccine should provide limited protection from this virus for adults, it provides no protection for young children.

It is not yet clear if these cases are just anomalies or the first signs of a serious trend, according to the MMWR dispatch, which stated, “Because these viruses carry a unique combination of genes, no information currently is available regarding the capacity of this virus to transmit efficiently in swine, humans, or between swine and humans.”

Go back to the current issue of the eConsult.