CDC reports two more novel flu infections

Dec 23, 2011 (CIDRAP News) – The US Centers for Disease Control and Prevention (CDC) today confirmed two more novel flu infections, one an H3N2 variant that has been identified in 11 other patients this year and one an H1N1 variant that has never been reported in humans before.

The CDC described the latest novel H3N2 case in an early-release article in Morbidity and Mortality Weekly Report (MMWR). The case, in a West Virginia child, involves a swine-origin H3N2 reassortant strain that includes the M gene from the 2009 H1N1 pandemic virus.

The CDC detailed the detection of the novel H1N1 virus in a "Have You Heard?" statement. The virus, also a triple-reassortant that has acquired the M gene of the 2009 H1N1 virus, sickened an adult in Wisconsin who had occupational contact with swine and has recovered.

The West Virginia child is a daycare contact of another child from West Virginia whose novel H3N2 infection was reported on Dec 9, the CDC said. The latest case turned up during an investigation to find out if any other children in the daycare were sick with the same virus. The second child, who is younger than age 5, got sick on Nov 29 with symptoms that included fever, cough, diarrhea, and rhinorrhea.

Like the first case-patient, the second child had no history of recent travel or swine exposure. The child did not seek medical care and has recovered fully, the CDC said.

A respiratory specimen obtained from the child on Dec 7 underwent rRT-PCR testing at the West Virginia Office of Laboratory Services, but the results were inconclusive. Genome sequencing at the CDC confirmed the virus as a novel H3N2 strain containing the M gene from the 2009 H1N1 virus.

The CDC said no other cases have been detected at the daycare or among the two children's contacts. West Virginia health officials and adjacent counties in Maryland are increasing their surveillance for flu-like illnesses, it added.

Though the two infections in West Virginia occurred in children who attended the same daycare, the CDC said the first child probably didn't transmit the virus to the second child, because their symptom onset dates were more than 10 days apart. However, it said the situation suggests limited human-to-human transmission in a daycare setting.

In late November, Iowa health officials reported two infections with the same H3N2 variant in two children who attended the same daycare.

The daycare setting is one of two scenarios that have been involved in the recent novel H3N2 cases, the CDC said. Though 11 of the 12 cases have occurred in children, one of the sick patients was an adult who had occupational exposure to swine.

The CDC said surveillance suggests the novel H3N2 virus is also circulating in swine herds. Of 150 swine influenza viruses that have been sequenced so far, 30 were H3N2 viruses, including 8 that had the M gene from the 2009 H1N1 virus. Further analysis is ongoing and new submissions to GenBank are being added as diagnostic work is completed, the agency said.

Regarding the novel H1N1 virus, the CDC said triple-reassortant viruses—ones that contain genes from avian, swine, and human flu viruses—have been circulating in US swine since the 1990s, and a review of genome sequencing databases suggests the variant that contains the M gene from the 2009 H1N1 virus has been found in US swine since 2010. But this case marks the first detection of such a strain in humans.

Testing shows that the virus is susceptible to the antiviral drugs oseltamivir (Tamiflu) and zanamivir (Relenza), the CDC said.

Given that the 2009 H1N1 virus is commonly circulating in swine and humans, the agency said, it isn't surprising to see viruses that typically transmit among pigs acquire gene segments from the 2009 H1N1 virus. CDC researchers are investigating the implications of the M gene in viruses that normally circulate in swine. So far, experiments suggest it makes flu more transmissible in guinea pigs, but it's not known if the same is true for pigs and humans.

In another development today, a working group from three health groups including the World Health Organization (WHO) recommended standardizing the terminology for the variant influenza viruses to help avoid confusion when referring to seasonal and other flu strains. For the novel H3N2 virus circulating in the United States, the group recommended using influenza A (H3N2)v, with the "v" standing for "variant."

The nomenclature working group also included members from the World Organization for Animal Health (OIE) and the United Nations Food and Agriculture Organization (FAO). The group said the novel H3N2 virus reported in the United States has not been detected anywhere else in the world.

The CDC said that, in line with the naming convention, it is calling the novel H1N1 virus H1N1v and the novel H3N2 virus H3N2v.

In seasonal flu news, the CDC said today that flu activity in the US was still at low levels last week. Doctor's visits for flu-like illness were still below baseline in all regions of the country, and the percentage of respiratory specimens testing positive for flu increased slightly from 1.9% to 2.1%, according to the weekly CDC surveillance report.

Deaths from pneumonia and flu dropped by a small amount and are at a level expected for this time of year, the CDC said, adding that no pediatric flu deaths were reported.

Meanwhile, the flu season in Europe doesn't appear to have started yet, with no sign of sustained transmission in any European Union countries so far, according to an update yesterday from the European Centre for Disease Prevention and Control (ECDC). It said all countries are reporting low flu activity, with 3.6% of respiratory specimens testing positive for flu. Most (88%) of the viruses that have been subtyped so far are seasonal H3N2, the ECDC said.

See also:

Dec 23 CDC weekly flu update

Dec 23 MMWR report

Dec 23 CDC "Have You Heard?" statement

Dec 23 joint statement on nomenclature

Dec 22 ECDC influenza update

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