Four North Carolina patients at a single hospital tested positive for a type of swine flu that is resistant to the medication Tamiflu, health officials said Friday.
The cases reported at Duke University Medical Center during six weeks make up the biggest cluster seen so far in the United States.
Tamiflu — made by Switzerland’s Roche Group — is one of two flu medicines that help against swine flu, and health officials have been closely watching for signs the virus is mutating, making the drugs ineffective.
More than 50 resistant cases have been reported in the world since April, including 21 in the United States. Almost all in the United States were isolated, said officials with the U.S. Centers for Disease Control and Prevention.
The BBC reported another cluster of five Tamiflu-resistant cases this week in Wales, in the United Kingdom.
The CDC has sent three disease investigators to North Carolina to help in the investigation there, 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, professor of medicine and director 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 they were very sick so it was hard to say it was the primary cause, he added.
North Carolina health officials did not disclose details about the four patients, other than that three of them — including the survivor — were women and their flu illnesses occurred last month and this month.
The first patient had been given Tamiflu before becoming ill with the virus, as a preventive measure. The three others were given Tamiflu after developing flu symptoms, Sexton said.
The case is under investigation, but hospital officials said they have no evidence the cases represent a hospital-wide concern.
The North Carolina cluster is unusual, but "at this time we don't have any information that should raise concerns for the general population," said Dr. Alicia Frye, epidemiologist in the CDC's flu division, in a prepared statement.
The only other reported U.S. instance of Tamiflu-resistant swine flu spreading from one person to another occurred about four months ago at a summer camp in western North Carolina, where two teenage girls — cabin mates — were diagnosed with the same drug-resistant strain. Health officials said at the time that the virus may have spread from one girl to the other, or it's possible that the girls got it from another camper.
