Clusters of resistant H1N1 cases reported in UK, US

Nov 20, 2009 (CIDRAP News) – Health officials in Wales today announced the identification of a cluster of patients in a Cardiff hospital who are infected with oseltamivir-resistant pandemic H1N1 influenza.

Also today, Duke University Medical Center in Durham, N.C., reported that oseltamivir-resistant H1N1 viruses were found in four very sick patients hospitalized there over the past 6 weeks. A Duke press release said all four patients had been in the same hospital unit, but it did not specify how many were there at the same time.

In Wales, the National Public Health Service (NPHS) said five patients in a unit at the University Hospital of Wales that treats people who have severe underlying health conditions have been diagnosed as having oseltamivir-resistant pandemic flu, and three of them appear to have been infected in the hospital.

Up to now, just one probable instance of person-to-person transmission of oseltamivir-resistant H1N1 flu has been reported. In September the US Centers for Disease Control and Prevention (CDC) reported oseltamivir-resistant pandemic H1N1 flu in two girls who stayed in the same cabin at a summer camp in western North Carolina.

Dr Roland Salmon, director of the NPHS's communicable disease surveillance center, said in the statement that the emergence of oseltamivir-resistant flu viruses isn't unexpected in patients who have serious underlying conditions and immune system compromise.

"In this case, the resistant strain of swine flu does not appear to be any more severe than the swine flu virus that has been circulating since April," he said.

All of the patients were treated with another antiviral medication. Two have recovered and have been discharged, and the other three remain hospitalized, one of them in critical care, the NPHS said. All other patients in the hospital unit have been tested for the virus, and health authorities are monitoring the patients' household contacts.

Dr Tony Jewell, NPHS chief medical officer, said in the statement that immunocompromised patients are known to be more susceptible to the pandemic flu virus and that health officials have strict processes for monitoring antiviral resistance and identifying it early.

"Identifying these cases shows that our systems are working, so patients should be reassured," he said, adding that oseltamivir (Tamiflu) is still appropriate treatment for pandemic flu and that patients should continue to take it when their doctors prescribe it.

Duke patients were immunocompromised
At Duke, officials said the four patients who had resistant viruses were in an isolated unit and were very ill, "with underlying severely compromised immune systems and multiple other complex medical conditions."

Daniel Sexton, MD, professor of medicine and director of the Duke Infection Control Outreach Network, said it is believed that all four patients caught the flu while at the hospital, the Associated Press (AP) reported today. He said three of the patients died and one is recovering.

One patient had been given oseltamivir as a preventive measure before experiencing flu symptoms, and the others were given the drug after symptoms developed, Sexton told the AP.

The university release said a team of experts from the CDC, state and county health departments, and the Duke Division of Infectious Diseases is investigating the cases.

"Our extensive investigation thus far has revealed that appropriate infection control procedures have been diligently practiced on this isolated unit, and throughout the hospital, and we have experienced no illness among employees taking care of these patients in the affected unit over this period of time," Sexton said in the release.

The statement noted that all oseltamivir-resistant H1N1 viruses identified so far have been susceptible to zanamivir (Relenza), the other licensed neuraminidase inhibitor.

Oseltamivir-resistant cases have been reported sporadically since the start of the H1N1 pandemic. In late October the World Health Organization said 39 cases had been identified up to that time. In general the cases have been geographically dispersed, and there has been no evidence of ongoing transmission of resistant strains, the European Centre for Disease Prevention and Control (ECDC) said this week.

Vincent Racaniello, PhD, a Columbia University virologist and author of Vriology Blog, said today there have been a few clusters of resistant H1N infections, but no sustained transmission of the strains. "I take this to mean that resistance strains do not transmit well among humans; otherwise, there would be more extensive circulation," he told CIDRAP News after he was asked to comment on the Wales cases.

"It took some time before seasonal H1N1 became widely Tamiflu-resistant [a fact that became clear last winter], and I suspect the same pattern will apply with 2009 H1N1 virus," he added. "At the moment there is no cause for alarm."

See also:

Nov 20 National Public Health Service for Wales press release

Sep 11 MMWR report

Nov 20 Duke University news release

Nov 19 ECDC report on resistant H1N1 strains

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