More New Zealanders than ever before are contracting the antibiotic resistant superbug MRSA.

But the number of people catching a lesser known bug, ESBL, is more worrying because it's harder to treat, medical experts say.

Environmental Science and Research reports 1042 cases of MRSA were recorded during last year's month-long survey - 288 more than the previous year.

The 37 per cent increase was the largest single-year rise in the past decade and signals a step towards a world where antibiotics are ineffective.

Medical Association deputy chairman Mark Peterson said the increase reflected the overall growth in superbugs both here and overseas.

"We've known about this increased resistance probably for a generation really and GPs and other doctors have become, over that period of time, much more careful with the use of antibiotics.

"We've had 70 years where we've been able to treat infections with antibiotics. We may, in another 70 years, not be able to treat [infections] anywhere near as well."

Resistance is caused by antibiotics being prescribed for viruses and people not taking their full course, the Health Ministry says.

People most at risk of a superbug infection are often hospital patients who are elderly or very sick, or who have an open wound, such as a bedsore, or a tube going into their body, such as a urinary catheter.

People can carry superbugs, which are transferred by contact, without having symptoms.

Laboratory tests are the only way to confirm if a person has a superbug.

Specific antibiotics could treat MRSA, Mr Petersen said, and GPs could manage infected wounds by cleaning and dressing them.

But ESBL was much harder to treat as it was resistant to a greater range of drugs.

Extremely sick patients and the elderly were more susceptible to ESBL bacteria, which adds to the difficulty in treating it as their bodies are battling other illnesses.

Serious infections could be treated by antibiotics via an intravenous line, but minor infections were usually left to run their course, Mr Petersen said.

Incidences of the lesser-known superbug have risen from 83 in 2001 to 578 in 2011.

The MRSA survey said there had been a return to it spreading in the community rather than in hospitals, though hospital patients were more at risk of contracting lethal strains. Of the 1020 people with it last year, just under half were in hospital.

Wellington Hospital's infectious diseases specialist Tim Blackmore said its "very low rates" of MRSA were the result of a successful hand hygiene programme.

Of the 3996 patients and staff specifically screened for MRSA last year, 35 people tested positive.

ESR collects MRSA and ESBL infection rates from district health boards every August. It does not collect information on how many people died from these infections.

- © Fairfax NZ News