Doctors are warning a powerful superbug could become deadly if it continues to spread in New Zealand at its present rate.

So far this year, 48 New Zealanders have tested positive to carrying the bacteria known as carbapenemase-producing enterobacteriaceae (CPE), up from 33 people last year. It was found in just 30 people in the six years from 2009 to 2014.

CPE are bacteria that produce an enzyme that deactivates a powerful group of antibiotics called carbapenems, meaning they are difficult to treat.

In most cases, the bug sits in the body, usually the bowel or gut, and causes no harm. But if it gets the bloodstream or urine it can be life threatening.

Of the 48 carriers identified this year, 16 had been infected - which meant they required urgent medical care. In all 16 cases, patients were cured and survived.

Counties Manukau District Health Board clinical director of infection services David Holland said treating those life-threatening infections would become more challenging as the bug spread.

"As has occurred overseas, over time, as these resistant bacteria become more common, they will cause deaths."

He said at the moment the risks were small in New Zealand but it was a concern for the next five to 10 years.

"We have to try to reduce the spread of these bugs as much as possible," Holland said.

He said his team were worried because there was a lack of effective antibiotics in New Zealand to kill the germs.

"Basically we need to buy time to develop new drugs to treat CPE."

Most people with CPE in New Zealand were believed to have been infected overseas - most commonly in China or India - and particularly if they had visited hospitals.

Counties Manukau DHB accounted for about half of the country's cases last year so the DHB needed to be on the frontline, Holland said.

"We are doing a lot of tightening up as well as introducing new safety measures to try to bend the curve and bring those rates down."

In August, about 600 Middlemore patients were tested after a person admitted to a ward was found to be carrying the CPE superbug.

Holland said the hospital now had a criteria that all at-risk patients, most commonly people who had been overseas and turned up to hospital with an unrelated illness, were screened.

"If patients tested positive for carrying the bug they were put into isolation and an alert was put on their file.

"If the patient was infected, for example the bug was in their blood stream, then we had to act quickly and find an antibiotic that would work to break it down."

University of Auckland associate professor of infectious diseases Dr Mark Thomas said these antibiotics were "last resort" drugs because they could cause toxic side effects.

"These germs are bloody hard to treat. It's a real disaster and nobody is going to make this problem go away. It's more a question of how fast it will spread and become a real problem."

What are CPE? 
They are bacteria in the bowel that can cause infections and are no longer treatable with certain antibiotics. There are very few antibiotics which can treat infections with carbapenem-resistant organisms and in extreme cases no antibiotics are effective.
They are common in many overseas countries but still rare in New Zealand.

How do people get CPE?
Widespread use of antibiotics has caused the development of resistant bacteria. It can spread between people through direct contact with each other or by touching items or surfaces that the carrier may have touched such as bed rails, toilets or equipment. New cases of the bacteria are usually associated with overseas travel.

What is the risk associated with carbapenem-resistant organisms?
People who have acquired it usually just "carry" it in their gut and suffer no consequences. However, if these people develop an infection then the carbapenem-resistant organisms​ may become involved. The main risk is to vulnerable patients while they are in hospital.