Western Australia is experiencing the worst outbreak of measles in the state for two decades, with 28 confirmed cases since the end of September and the latest confirmed on Friday.

Key points: A "super-spreader" from New Zealand has been blamed for 22 of the measles cases

A "super-spreader" from New Zealand has been blamed for 22 of the measles cases Health officials have been in a race against time to find anyone exposed to the virus

Health officials have been in a race against time to find anyone exposed to the virus Over 1,000 people have been contacted and some of them placed in isolation

The outbreak worsened with confirmation another person had been diagnosed as carrying the illness while visiting several public places in the Perth metropolitan area between October 17 and 20.

The person has potentially exposed people around the southern Perth suburbs of Jandakot and Hamilton Hill, particularly at the Hamilton Hill Shopping Plaza.

They were also infectious while visiting the Pear Tree Cafe, a Bakers Delight bakery, a local IGA supermarket and a First Choice liquor store.

The latest infection has taken the number of measles notifications in WA to 54 for the year to date.

'Race against the clock' to stop outbreak spreading

The WA Health Department treats every measles case as a public health emergency and the latest cluster has been handled in much the same way as a bushfire or a cyclone.

Dozens of additional staff have been mobilised and are working around the clock to track down people who may have been exposed to the incredibly infectious disease.

Medical professionals are required by law to notify the department every time a person is suspected of having measles.

The Communicable Disease Control (CDC) directorate has staff on call 24 hours a day, and as soon as a notification comes in the team springs to action.

The infected person is placed in isolation and treatment is commenced while the directorate retraces their every movement in forensic detail.

CDC director Paul Armstrong said some people with measles expose up to 400 other people to the virus before it is detected.

Paul Armstrong says health officials are hopeful the outbreak will soon be over. ( ABC News: James Carmody )

He said it had become "a race against the clock" for the Health Department to get in touch with each of them.

"Because measles is so infectious, it picks out those small number of people who don't have immunity, so we have to put a lot of effort into contacting those people we know about," he said.

If discovered within six days of initially being exposed, a person can be effectively vaccinated against measles or treated with medication before the infection takes hold.

This can prevent further spread of the infection and is particularly urgent for vulnerable groups, such as people with immune deficiencies, pregnant women and babies, for whom measles can be deadly.

Patient zero from New Zealand was a 'super-spreader'

Of the 28 cases detected, the Health Department said five of those people picked up measles while overseas, but it is believed the infections of at least 20 people could be traced back to one man who visited Perth from New Zealand.

"It's very unusual to get so many cases emanating from one particular case," Dr Armstrong said.

"There's a term we use sometimes in infectious diseases epidemiology called a 'super-spreader' and this fellow seems to be a 'super-spreader'.

"He was sick for his whole time that he was in Western Australia and he travelled widely — he was on holidays, going to lots of different places, shopping centres and other places."

Authorities say the last time WA had a measles outbreak of similar levels was in 2006. ( ABC News: James Carmody )

The man's homeland of New Zealand is currently suffering a massive measles epidemic, with more than 1,800 cases detected and two women suffering miscarriages attributed to measles.

Dr Armstrong said the Health Department was hopeful the latest outbreak in Perth would soon come to an end, but he warned there would be a risk of similar outbreaks in Australia as long as the epidemic in New Zealand continued.

"It's really quite a big problem there, and because we have so many people travelling to New Zealand and also New Zealand-born people who live in Western Australia and other parts of Australia, there's a lot of traffic between those two countries," he said.

More than 1,000 people exposed

The head of the Metropolitan Communicable Disease Control division, Ben Scalley, said a number of people in WA had been successfully placed into isolation or treated as a result of thorough "contact tracing", which had seen more than 1,000 people contacted by the Health Department.

Ben Scalley and his department have been in a race against time to control the outbreak. ( ABC News: James Carmody )

"We check on what workplace they work in, how they got to work, what train they caught, what bus they caught, where they drove their car, who they went out with in the evening, who is in their house, who visited the house, the pizza delivery person, in really quite a degree of detail to try and capture every single person they have been in contact with," he said.

"Typically, when we have a case of measles, that person has been to two or three medical facilities, be they GPs or emergency departments. Often they've worked or gone to school and often they've had a number of social outings or been to a supermarket or something like that.

"Of the additional cases that we've had lately, most of them have actually been people where we've caught it just in time and we've kept them home from work or school.

"Those people have had essentially no further contacts, just those in their house, and we've been able to control that."

The last time Western Australia had a measles outbreak of similar proportions was in 2006 when a touring Indian guru infected dozens of people throughout the country including 26 in WA.

Unexplained cases of measles are almost non-existent in Australia now, with the disease officially eliminated in the country in 2014 and the only cases since then originating from overseas.

That has been attributed to an effective vaccination program which has seen most Australians receive at least one measles vaccine, and many receive a second which is required for full immunity.

Travellers ignoring infection risk

Despite this, the World Health Organisation has reported a 50 per cent increase in measles worldwide in the past few years, and Dr Armstrong said Australians needed to be wary of that when travelling.

Health officials think they're on top of the outbreak but say WA isn't out of the woods yet. ( ABC News: James Carmody )

"Whenever a person goes overseas to South-East Asian countries or lots of other countries as well, who isn't immune to measles, then they put themselves at risk," he said.

"A lot of Western Australians treat Bali as if it's Bunbury, Broome or Busselton, but the difference is that when people go to these countries, they are developing countries [and] they have a different set of diseases.

"People don't seem to think about that as much as they should, so they don't get vaccinated, they don't wear clothes that will stop them from getting bitten by mosquitoes and they don't take other precautions which will prevent them from getting infections."

The Federal Government's chief medical officer, Brendan Murphy, said he advised people get the measles vaccination before travelling to New Zealand or anywhere else overseas.

"Measles is one of the most infectious viruses we know, it's almost certain you'll get it if you're not immune and you are exposed," he said.

"Everybody who is travelling internationally should consider measles as a travel vaccination."

"If you're not sure that you have had two doses of the vaccine, go and get another one before you travel, it's harmless to get a third vaccine if you've had two."

The canary in the anti-vaxxer coal mine

Dr Murphy said unfortunately, there had been a wealth of misinformation published about measles vaccinations in the past, with fraudulent research indicating it caused autism having been completely debunked.

"Some of the anti-vaxxer groups are still pedalling that myth out there and so it is one of the reasons we're very keen to get the message out there of the importance and the utter safety of vaccination," he said.

"I always regard measles as a canary in the coal mine, because it's such an infectious disease, any risk in population immunity will be picked up.

"It is a worry to us that it points out those areas of our community where there might be low uptake of childhood immunisation, because half of these 235 cases [of measles in Australia this year] are in younger people, and some of those it's because they've just not had the properly provided childhood immunisation."

The latest measles case in WA was discovered on Wednesday, but Dr Armstrong was confident the outbreak was nearing an end.

"We feel like we're getting on top of it. [But] we're not out of the woods yet … and if we have another spate of cases then the whole thing starts again," he said.