A new study has shown that patients infected with carbapenem-resistant Enterobacteriaceae (CRE) could take over one year to be rid of CRE bacteria.

CRE, according to the U.S. Centers for Disease Control and Prevention (CDC) are potentially deadly infections that are highly resistant to antibiotics, making them difficult to treat. Though the bacteria is not normally found in healthy people, patients on ventilators, patients with catheters, or those on long courses of antibiotics are at risk for infection.

The study, published in the American Journal of Infection Control, looked at 97 CRE-positive patients who were discharged from the Shaare Zedek medical Center from 2009 to 2010. It showed that patients who tested positive for CRE took an average of 387 days to clear the infection. Even after one year, 39% of the patients remained “positive” for CRE, meaning they could become re-infected or transmit the infection to other people.

“Patients with multiple hospitalizations or those who were diagnosed with clinical CRE disease should be assumed to have a more extended duration of CRE coverage and should therefore be admitted under conditions of isolation and cohorting until proven to be CRE-negative,” said the study’s authors. “These measures will reduce the hospitalization of CRE-positive patients among the general patient population, potentially preventing the spread of CRE.”

The study was also able to identify several risk factors that were related to long periods of infection, including long hospital stays, re-hospitalizations, and whether patients had an active infection or a “colonization” without symptoms.