A Puerto Rican hospital's intensive care unit was recently closed following an outbreak of a resistant bacteria strain, health officials revealed Tuesday.

At least 10 patients at the University of Puerto Rico Hospital in the northern city of Carolina who have since died were carrying the bacteria Acinetobacter baumannii, said Dr. Haydee Garcia, epidemiology director of the island's health department.

She said eight of the patients did not die from the , but it's unclear whether the bacteria caused the deaths of the other two.

The deaths occurred between May and July and prompted Garcia to ask the U.S. Centers for Disease Control and Prevention to investigate.

"When this bacteria appears, it's a concern," she said. "It's not normal for humans to carry that bacteria."

Garcia blamed the presence of the bacteria on , saying an investigation found that medical personnel were not following basic procedures such as frequently washing their hands.

The bacteria usually occurs in intensive care units and is responsible for some 80 percent of reported infections, according to the CDC website.

It is unclear how many deaths the bacteria might have caused in Puerto Rico compared to the U.S. mainland. CDC spokeswoman Melissa Dankel said those statistics were not available.

Dankel referred other questions about the outbreak to Garcia, noting that the CDC was invited to investigate.

Garcia said the , which is being remodeled, has since tested negative for the bacteria.