Nearly 180 patients are believed to have been exposed to an antibiotic-resistant "superbug" at a California hospital, medical officials told the Associated Press.

So far, there have been seven confirmed cases of Carbapenem-Resistant Enterobacteriaceae, CRE, at the Ronald Reagan UCLA Medical Center in Los Angeles. Two of those patients have died.

Drug tests performed on one of the patients in January revealed the infection was caused by the use of contaminated medical instruments named endoscopes, UCLA spokesperson Dale Tate told the AP.

Officials now believe a total of 179 patients who stayed at the hospital from October 2014 to last month could have been infected with CRE. Home testing kits have been sent to those exposed. It has not been confirmed if the deaths of the two patients were caused by CRE, but it may have been a "contributing factor," the university said.   

Symptoms of CRE, which is resistant to most antibiotics, include an infection in the lungs or bladder followed by fever and coughing. Fifty percent of patients die if the infection spreads to the bloodstream.

A CRE outbreak at a Virginia hospital earlier this year saw 32 patients infected. Eleven of those patients died, but officials said other factors could have caused the deaths.

"This bacteria is emerging in the U.S. and it's associated with a high mortality rate," Dr. Alex Kallen, an epidemiologist with the Centers for Disease Control and Prevention, told the Los Angeles Times. "We don't want this circulating anywhere in the community."

University officials traced the source of the outbreak to endoscopes that were placed down patients' throats to help treat diseases of the digestive track. The devices are used on about 500,000 patients a year, according to the LA Times.  

"We notified all patients who had this type of procedure, and we were using seven different scopes," Tate told the AP. "Only two of them were found to be infected. In an abundance of caution, we notified everybody."

The two endoscopes in question underwent the proper sterilization before the outbreak was discovered. Both instruments have since been removed "and we have heightened the sterilization process," Tate said.