The number of cases in WA’s worst diphtheria outbreak has risen to 85, as health officials seek to boost vaccinations rates of the illness in vulnerable communities.

The cases have been almost exclusively in WA’s northern-most region of the Kimberley, with 78 reported in that area, while a handful have been detected in the Pilbara and Goldfields.

It is also the first time in 50 years the respiratory form of the infection has been seen in WA.

Nearly 95 per cent of the case have been in the Aboriginal community, especially among children and young people.

Authorities are concerned many in the region are behind on their vaccinations against the disease.

An expanded vaccination program has been rolled out in the State’s north, focusing on active catch-up vaccination for children and adolescents who are not up to date with routine immunisations.

Communicable Disease Control Directorate director Paul Armstrong said work was underway to quell the outbreak.

“WA Health has significantly strengthened its public health response over recent months, including expanded vaccination activity, case management, contact tracing and ongoing community engagement across affected regions,” Dr Armstrong said.

“While most cases have occurred in the Kimberley, the Department continues to closely monitor the situation across regional WA and respond as appropriate.”

The respiratory strain of the infection often begins with cold-like symptoms of a sore throat, fever and chills before escalating to cause a thick greyish-white coating in the back of the nose or throat and swollen or painful glands in the neck.

It can worsen to make it difficult to swallow and breathe, becoming life-threatening.

There is also a skin infection form of diphtheria, which stats from an infected wound and presents as sores or ulcers — often on the legs — which may be slow to heal and may be covered with a grey, moist scab.

Diphtheria spreads through close contact with an infected person such as breathing in droplets from coughing or sneezing as well as direct contact with bodily fluids like saliva or contaminated objects such as bandages.

Dr Armstrong said while the risk to the rest of the State was low, Health authorities were ready to act if needed.

“The risk to the broader Western Australian community remains low,” he said.

“WA Health will continue to closely monitor the situation and implement additional public health measures as required.”