Middlemore Hospital in South Auckland has stepped up superbug checks, after two patients were found to have bacteria that can be resistant to most antibiotics.
The bacteria are called CPE - carbapenemase-producing enterobacteraceae.
The two patients were not sick with infections caused by CPE; instead, they were carrying the potentially-harmful bacteria in their gut, without symptoms.
"The organism was found in both patients by routine screening of the patients' gut organisms," said the Counties Manukau District Health Board.
"Counties Manukau Health has intensified routine surveillance for antibiotic resistant bacteria at Middlemore."
That is mandated by the declaration by the Ministry of Health of several Middlemore wards as a "transmission risk area".
Infectious diseases specialist Dr David Holland said, "This means that if there is a possibility of the organism being acquired in the hospital from a patient or environment source, either known or unknown, this triggers intensive investigation and reinforcement of infection control measures."
He said no connection between the two patients had been established; nor had a source been identified.
"It is important that we take every precaution to ensure we identify anyone else who may be carriers of CPE and, if possible, the source of these CPE."
The first CPE carrier to be identified was a surgical patient in November, followed by the second patient, who acquired the organism on a different ward about nine days later.
Screening involves doing lab tests with a faecal sample or rectal swab.
The DHB said that to prevent further CPE transmission, all patients who have had an admission for 24 hours to Middlemore surgical wards - excluding maternity - since October 31 will be screened for CPE and other antibiotic-resistant bacteria if they had been admitted to other health or aged-care facilities.
Holland said patients discharged home from the surgical wards since October 31 need not take any special action as the mere presence of CPE in the gut/bowel did not require treatments.
Most people who have CPE are carriers. Only rarely does it cause symptomatic infections, such as in the urinary tract or bloodstream, in surgical wounds, and in people who are critically ill or receiving chemotherapy.
Holland said the other 19 DHBs would be told of the need to screen patients on admission if they had been on a transmission-risk-area ward at Middlemore since October 31.
CPE was relatively rare in New Zealand although the number of people detected with it at hospitals had increased in recent years.
The bacteria could live in the gut for months to years and in that site cause no harm.
"There is no effective way to remove it from the gut and it may stay for longer if you take antibiotics."
The best way to prevent the spread of CPE is by good hygiene, including hand-washing.
• Those who are concerned they may have been exposed to CPE are urged to call Healthline on 0800 611 116.