The Ministry of Health says a superbug affecting two hospitals in Auckland has the potential to affect hospitals nationwide.
At the peak of the outbreak in April, 245 patients in North Shore Hospital and Waitakere Hospital caught extended spectrum beta lactamase (ESBL).
Five elderly patients who had the superbug, but also had other illnesses, died in the nine months to April.
Improved hygiene measures reduced the number of infections to 162 in August.
The ministry's chief advisor on population health, Dr Greg Simmons, says hospitals are taking extra precautions, particularly with patients who have been in hospitals overseas.
People who have recently been in a hospital overseas will have swabs taken, and if ESBL is present, measures will be taken to ensure it does not spread to other patients.
Waitemata District Health Board may have to consider splitting hospital wards in an effort to control ESBL.
Patients at North Shore Hospital are divided between three rooms, one for those that test positive for the superbug, another for those waiting for results and a third for those that have been cleared.
But staff shortages mean some nurses work in more than one room during their shift.
Now the hospital is to ask the district health board to consider splitting medical and surgical wards to ensure patients with the bug have separate staff from those that don't.
The superbug is usually carried in the bowel, but can be fatal if it crosses into the bloodstream.