GREENVILLE, S.C. - Greenville Health System says it will expand a new water filtration system to all of its campuses to prevent the type of outbreak that infected 15 patients and may have led to four deaths.

The Greenville News reports that medical quality director Dr. Robert Mobley Jr. said installation of the new filtration system is an extraordinary measure, but one the system has taken on to protect patients.

"The measures we've taken will make us an even better, safer place," Mobley said.

Officials said last month that 14 people tested positive for atypical Mycobacterium abscessus. Most of them had cardiac surgery, while two had abdominal surgery and one a neurological operation. Officials think the infection may have been spread by health workers using tap water before surgery.

Mobley said it remains a mystery as to how the patients were infected by tap water. The first patient recognized with the infection tested positive in March.

Mycobacterium abscessus is common in the environment, typically found in soil and water, according to the U.S. Centers for Disease Control and Prevention. Healthy people drink it and bathe in it with no problem and officials say it's safe to use.

State health officials issued a statement earlier this week saying that consuming even high levels of Mycobacterium abscessus isn't typically a risk for infection.

But it has been known to cause infections in surgical patients, though that's rare, according to CDC, which investigates about half a dozen cases a year.

GHS said the patients who were infected suffered from some serious underlying health conditions that could have made them more susceptible. Mobley said he couldn't divulge the nature of those conditions for confidentiality reasons.

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Information from: The Greenville News, http://www.greenvillenews.com