# 5976
For the past several months we’ve been watching an evolving story involving a newly identified swine flu variant (S-OtrH3N2) that has now been detected in 10 people (mostly children) across 4 states.
For more on those earlier cases see:
CDC Update On trH3N2 Swine Infections
Maine Confirms A 2nd trH3N2 Case
CDC Update On trH3N2 Cases
A 5th trH3N2 SOIV Report
CDC Update On Recent Novel Swine Flu Cases
MMWR: Swine-Origin Influenza A (H3N2) Virus Infection in Two Children
Although the majority of these cases have had recent potential contact with swine, the latest three cases out of Iowa appear to be the result of Human-to-Human (H-2-H) transmission.
Late yesterday the CDC released a special MMWR dispatch that provides details on these three new cases, some background on earlier SOIV (swine origin influenza viruses) cases, and some analysis.
A few excerpts follow (underscores & bolding mine), but follow the link to read the entire dispatch.
Limited Human-to-Human Transmission of Novel Influenza A (H3N2) Virus — Iowa, November 2011
Dispatch
November 23, 2011 / 60(Dispatch);1-3On November 20, 2011, CDC confirmed three cases of swine-origin triple reassortant influenza A (H3N2) (S-OtrH3N2) virus infection in children in two counties in Iowa. None of the children were hospitalized, and each has recovered from a mild episode of febrile respiratory illness. All three were in contact with one another, and none had a known recent exposure to swine. No additional human infections with this virus have been detected in Iowa, and no evidence of sustained human-to-human transmission of this S-OtrH3N2 virus exists; surveillance is ongoing.
Eighteen human infections with swine-origin influenza A (H3N2) viruses have been identified since 2009 (1,2). The most recent 10 cases, including the three Iowa cases described in this report, were infections with S-OtrH3N2 viruses containing the matrix (M) gene from the pandemic 2009 influenza A (H1N1) virus (pH1N1). These viruses are considered reassortant viruses between a swine-origin influenza A (H3N2) virus circulating in North American swine and a pH1N1 virus. All cases of human infection with S-OtrH3N2 virus containing the M gene from the pH1N1 virus have occurred in 2011 and have been reported from four states: Pennsylvania (three cases), Maine (two), Indiana (two), and Iowa (three) (3).
Case Reports
Patient A. In the second week of November 2011, patient A, a previously healthy female child, experienced acute onset of influenza-like illness (ILI). Three days after her illness onset (illness day four), she was seen by a health-care provider, who obtained a respiratory specimen and performed a rapid influenza diagnostic test, which was positive.
As part of routine influenza surveillance, the respiratory specimen was forwarded to the University of Iowa State Hygienic Laboratory (SHL) for further evaluation. Patient A's brother experienced onset of ILI 1 day before patient A's date of illness onset. Patient A's brother was not tested for influenza but was treated with oseltamivir by a health-care provider and has recovered. During her illness days two and three, patient A was in contact with her father, who subsequently developed ILI 2 days after his most recent contact with patient A. He was not tested for influenza. No other household member has reported respiratory illness. No family member reported exposure to swine before their illness onset. On her illness day one, patient A attended a small gathering of children.
Patients B and C. Patient B is a previously healthy male child who developed ILI 2 days after patient A's first day of illness. He is the sibling of patient C, a previously healthy male child who developed ILI 1 day after patient B's illness onset. Both children were seen by a health-care provider 2 days after patient B's illness onset; rapid influenza diagnostic testing was positive for both patients. As part of routine influenza surveillance, respiratory specimens were forwarded to SHL for further evaluation. The mother of patients B and C reported that no other household member had a respiratory illness and none had been exposed to swine before patient B became ill. On patient A's illness day one, patients B and C attended the same small gathering of children as patient A.
Epidemiologic and Laboratory Investigations
An investigation by the Iowa Department of Public Health (IDPH) determined that the families of patients A, B, and C reported no recent travel or attendance at community events. To date, the only epidemiologic link among patients A, B, and C that has been identified is attendance at a gathering of children on patient A's illness day one. No illnesses were reported among adults or among the five other children who were present at this gathering on that day. No swine exposures have been identified among adults or children attending this gathering. IDPH has detected no increase in absenteeism or reports of respiratory illness in the community where patients A, B, and C reside or in the schools in the community.
Enhanced surveillance for ILI has been implemented in health-care facilities in the communities where patients A, B, and C reside. IDPH has instructed health-care providers to obtain respiratory specimens from patients with ILI for influenza diagnostic testing at SHL. Thus far, no additional cases of S-OtrH3N2 infection have been identified, and surveillance data from the state have shown low levels of influenza activity currently and at the time of all these patients' illnesses.
Swine are highly susceptible to the influenza virus, and are capable of serving as `mixing vessels’, allowing them to reassort into new hybrid strains.
Reassortment happens when two different influenza viruses co-infect the same host, swap genetic material, and produce a hybrid virus.
That is essentially what happened in 2009, when the H1N1 swine flu virus emerged after bouncing around swine herds for a decade or more, picking up genetic changes along the way.
And not surprisingly, this recently emergent `humanized’ H1N1 virus has re-entered the swine population and is once again mixing and matching with other circulating swine flu viruses.
As a result we now have a Swine H3N2 virus that has reassorted with the 2009 pandemic H1N1 virus, producing a new hybrid that has – in a limited fashion – begun to emerge into the human population.
Whether this virus has `legs’, and can sustain itself in the human population, is something we’ll simply have to wait to see.
Regardless of what this virus does - with our regular flu season nearly upon us - the best advice from the CDC is to maintain good flu hygiene this winter (cover your coughs, wash your hands, stay home if you are sick), and to get the seasonal flu shot.
While the public health threat from this emerging swine virus appears low for now, this is obviously a story we’ll continue to follow with considerable interest.
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