The discovery of a superbug at Dunedin Hospital highlights the need to prescribe antibiotics only when necessary.

Five patients recently admitted to the Hospital have tested positive for a bacteria which is resistant to antibiotics.

Southern DHB chief medical officer Dr Nigel Millar said it's a strain of common bacteria called enterococcus, which is resistant to antibiotic treatment, Vancomycin.

"For the people where it's been found it's only colonised, it's not causing infection, so it's not harming anyone at the moment. But the risk is if it were to spread any further through a lot of people maybe some of them would become unwell."

Dr Millar said they've taken steps to prevent any further spread - screening those who've been in proximity to affected patients - and feel it's under control, but there's always the concern if people became unwell, it would be hard to treat.

"This particular strain there are other antibiotics available to us, which we would expect to work, they are more complicated to use and have more side effects so that is a concern for us."

He said it does highlight the ongoing concern that unless antibiotics are used carefully, and somewhat sparingly, we will end up with more resistant bacteria that are difficult, and in some cases impossible, to treat.