Parts of Middlemore Hospital have been declared 'transmission risk areas' after two patients were found to be infected with a bacteria resistant to most drugs.
The bug was first identified by Counties Manukau Health in a surgical patient in November. A second patient contracted it in another ward nine days later.
Neither reported feeling unwell as a result of the infection, and the hospital is playing down fears of an outbreak.
Both infections were discovered during routine gut screenings.
The organism is what's known as a carbapenemase producing enterobacterales/enterobacteriaceae (CPE). They produce carbapenemase, which disables carbapenem antibiotics. If those drugs don't work, then doctors are required to use even stronger antibiotics.
Microbiologist Siouxsie Wiles told Newshub in August the drugs needed to kill CPEs are "not very nice drugs at all", and only used as a last resort.
The bugs can survive in 'colonised' people's guts, throats and nose without causing any problems. But if drug-resistant bacteria end up in the bloodstream or the lungs, or anywhere else they're not meant to be, that's an infection and with present medicine, death usually follows, Dr Wiles said in August.
All patients who have spent more than 24 hours in a Middlemore Hospital surgical ward since October 31 will be screened for the organism next time they're admitted or see a doctor.
"The minimum recommended screening will involve a faeces specimen or rectal swab," said infectious diseases consultant David Holland.
"Any positive result would result in further reinforcement of measures to prevent spread of the organism. There is no treatment necessary for simple presence of the organism in the bowel... The bacteria can be in the gut for months to years and in that site will cause no harm."
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There is no clear link between the two infected patients, Dr 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."
Anyone who fears they may have been infected should call Healthline on 0800 611 116.