Tamiflu-resistant swine flu cluster reported in N.C.

Four North Carolina patients at one hospital tested positive for a type of swine flu that is resistant to Tamiflu, health officials said yesterday.

The cases reported at Duke University Medical Center over six weeks make up the biggest cluster seen so far in the U.S.

Tamiflu -- made by Switzerland's Roche Group -- is one of two flu medicines that help against swine flu. Health officials have been closely watching for signs that the virus is mutating, making the drugs ineffective.

About 52 resistant cases have been reported in the world since April, including 15 in the U.S. Almost all in the U.S. were isolated, said officials with the U.S. Centers for Disease Control and Prevention in Atlanta.

The BBC reported a cluster of five Tamiflu-resistant cases this week in Wales.

The CDC has sent three disease investigators to North Carolina to help in the investigation, said Dave Daigle, a CDC spokesman. CDC testing confirmed the Tamiflu-resistant cases.

All four cases at the hospital were very ill patients in an isolated cancer unit, and it is believed they all caught the flu while at the hospital, said Dr. Daniel Sexton of the Duke Infection Control Outreach Network.

Three of the four patients died, and one is recovering, he said. Flu seems to have been a factor in each death, but the patients were very sick and it was hard to say that it was the primary cause, he added.

The North Carolina cluster is unusual, but "at this time we don't have any information that should raise concerns for the general population," Dr. Alicia Frye, epidemiologist in the CDC's flu division, said in a statement.

Meanwhile, the World Health Organization said yesterday that it is investigating samples of variant swine flu linked to two deaths and one severe case in Norway, but that so far the significance of the mutation is unclear.

Norway's Institute of Public Health announced yesterday that the mutation "could possibly . . . cause more severe disease" because it infects tissue deeper in the airway than usual.

The same mutation has been found in fatal and mild cases elsewhere, including in Brazil, China, Japan, Mexico, Ukraine, and the United States, said WHO.

WHO said that anti-viral drugs still appear to be effective against viruses with the mutation.

Virus mutations occur spontaneously, and many have no effect on the danger a virus poses to humans.