Mecklenburg County health experts said Friday they're keeping an eye on a drug-resistant type of swine flu that infected four patients at a single hospital in North Carolina.

• VIDEO: Tough New Swine Flu Strain Surfaces In North Carolina

State health officials confirmed that three women and a man being treated at Duke University Medical Center over the last six weeks developed a new "mutated" form of the H1N1 virus.

State Epidemiologist Dr. Megan Davies said, "Three of those patients have died although it is not clear if those deaths were related to their flu infections."

Doctors said that's because all four patients suffered from other medical conditions that compromised their immune systems.

Duke doctors tried treating all of the patients with Tamiflu but saw no results.

The Centers For Disease Control (CDC) confirmed Monday night the mutated H1N1 virus is resistant to the widely used drug.

The surviving woman is now being treated with the drug Relenza and is recovering, but doctors said Tamiflu will still be a part of their arsenal against H1N1.

State Epidemiologist Dr. Zack Moore said, "Tamiflu is still considered to be an effective medication."

Doctors said Tamiflu has a 99 percent response rate in patients.

State health leaders said clusters of the mutated swine flu virus appear to be rare and isolated.

This is the second instance in North Carolina. There have been 21 cases in the U.S. and a little more than 50 mutated cases reported in the world.

The Gastonia Parish Nurse Ministry and Maxim Healthcare Services offered H1N1 vaccines to people in high risk groups Saturday.

The clinic was at the First Presbyterian Church of Gastonia on East Garrison Boulevard in Gastonia.

The clinic was open from noon until 5 p.m.