Peer-reviewed literature

02 December 2011

The Centers for Disease Control and Prevention (CDC) of the United States of America (USA) reported (Prescott et. al. 2011) on 23 November 2011 on three cases of a novel influenza virus in children in the USA. The virus is a swine-origin triple reassortant influenza A(H3N2) (S-OtrH3N2) virus containing the matrix (M) gene from the A(H1N1)pdm09 virus; this is a reassortment of a swine-origin A (H3N2) virus circulating in North American swine with the pandemic virus. These three are the 8th, 9th, and 10th cases of human infection with S-OtrH3N2 viruses with the M gene from the A(H1N1)pmd09 virus, all of which have occurred in 2011 in the USA; however, in the previous seven cases, either the patient or a close contact of the patient had recent exposure to swine. The current three cases, which are epidemiologically linked, but have no known exposure to swine, suggest that limited human-to-human transmission of this novel influenza virus may have occurred. The virus isolated from all three patients is resistant to amantadine and rimantadine but susceptible to the neuraminidase antiviral medications oseltamivir and zanamivir. Of the 10 cases of this novel virus identified thus far in 2011, seven cases resulted in mild illness, three were hospitalized for influenza (none of the three children described in the current report were hospitalized), and all have recovered. Based on preliminary evidence from the case investigations, there is no evidence of ongoing sustained transmission among humans, and there is no evidence that the swine influenza viruses which spread amongst pigs are spread through human contact with pork or pork products. Due to the unique combination of genes in the virus, their potential to transmit efficiently in swine, humans, or between swine and humans is currently unknown. The communities where the current patients reside have intensified surveillance and respiratory specimens from all patients presenting to health care providers with influenza-like illness are being collected and sent for diagnostic testing.


At the time of writing, no further cases of this novel virus have been reported, though investigations are ongoing. This report highlights the value of an effective influenza surveillance system with both epidemiological and virological components. In addition, WHO recommends that unusual clusters of influenza-like illness or severe acute respiratory infection should be reported and investigated. All influenza specimens that are unsubtypeable as well as specimens with inconclusive or unexpected subtyping results should be forwarded to a WHO Collaborating Center for Influenza or WHO Essential Reference Laboratory as soon as possible for additional testing.


Prescott K, et. al. "Limited human-to-human transmission of novel influenza A (H3N2) virus - Iowa, November 2011". CDC Morbidity and Mortality Weekly Report (MMWR), December 2, 2011 / 60(47);1615-1617.

WHO Regional Office for the Americas, Epidemiological Alerts and Reports, 25 November 2011 Influenza like Illness.

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