Unusual Influenza Virus Discovered in US Kids, CDC Reports

September 02, 2011

September 2, 2011 — The US Centers for Disease Control and Prevention (CDC) today reported that a form of swine-origin influenza containing a genetic segment of the 2009 influenza A (H1N1) virus infected 2 children in Indiana and Pennsylvania this summer, a development that has prompted vigilance about possible ongoing transmission.

"Non-human influenza virus infections rarely result in human-to-human transmission, but the implications of sustained ongoing transmission between humans is potentially severe," the CDC stated in the Morbidity and Mortality Weekly Report published online September 2.

Aaron Glatt, MD, a fellow with the Infectious Diseases Society of America, told Medscape Medical News that the CDC report justifies ongoing surveillance of the situation, but not a sense of alarm.

"There's no reason to think this is an urgent news flash," said Dr. Glatt, president and chief executive officer of St. Joseph Hospital in Bethpage, New York. "It's of more interest to scientists than to the public."

The children, both younger than 5 years, recovered from their infections, according to the CDC. One of the children, a boy in Indiana with multiple chronic health conditions, had no known direct exposure to pigs, although a caretaker reported having direct contact with asymptomatic pigs in the weeks before the onset of the boy's illness in July. The other child, a girl in Pennsylvania, reportedly had visited an agricultural fair on August 16, where she was exposed to pigs.

Both children had received influenza vaccine in September 2010. Neither was treated with antiviral medications.

The CDC states that both children were infected with a swine-origin influenza A (H3N2) virus. Similar swine-origin viruses have caused a scattering of human infections in recent years, but the viruses detected this summer are unique because in both cases, they possessed the matrix (M) gene, which is 1 of the 8 gene segments found in the 2009 influenza A (H1N1) virus.

Because the Indiana boy did not have known direct exposure to swine, the CDC is not ruling out "the possibility that limited human-to-human transmission of this influenza virus occurred." Such transmissions of swine-origin viruses have occurred in the past, but not on a sustained basis.

Preliminary evidence in the Indiana case indicates there is no ongoing transmission there, the CDC stated, but the agency warned that "if additional chains of transmission are identified rapid intervention is warranted [to] try to prevent further spread of the virus."

The agency is advising clinicians to consider swine-origin influenza A virus infection in addition to the seasonal influenza in any patients with febrile respiratory illness who have been near pigs. If they suspect influenza infection in such individuals, they should obtain a nasopharyngeal swab and arrange to have it shipped to a local or state public health department for testing. They also should consider treating these patients with either oseltamivir or zanamivir.

Morb Mortal Wkly Rep. Published online September 2, 2011. Full text

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