Health officials in Australia were considering making vaccines mandatory for ambulance workers after a paramedic infected with the virus visited four hospitals and put thousands at risk. Above, a vial of the measles, mumps and rubella vaccine is pictured. Reuters/Brian Snyder

As many as 4,500 people could be sickened by measles after a paramedic infected with the highly contagious virus visited four hospitals and a tourist site, officials in the state of Queensland, Australia fear. The paramedic represented the eighth case of measles in Queensland in 2015.

Tourists were among those potentially infected as Queensland health officials sought to trace who had come into contact with the paramedic as well as where he himself picked up the infection. Between Thursday and Monday, without realizing he had contracted the virus, the paramedic had transported patients to four different public hospitals in Queensland, Australian news site the Morning Bulletin reported.

The paramedic, reportedly in his early 30s, is now in the hospital and seriously ill, although his condition was reported as stable. It was unclear whether the paramedic had been vaccinated against the disease, whose symptoms include fever, cough, rashes and a runny nose, all of which can lead to complications including brain inflammation, according to the CDC.

In Queensland, ambulance workers were encouraged but not required to be immunized against all vaccine-preventable diseases, although Queensland Health Minister Cameron Dick has said that could change. "I have this morning asked my department to examine the feasibility of having all ambulance officers in the Queensland Ambulance Service vaccinated against measles,” he said, the Brisbane Times reported Wednesday. He would also consider a broader vaccination program for all health workers. Overall, Australia’s vaccination rate against measles stands at a fairly robust 94 percent, according to data from the World Health Organization.

Health workers are currently required to be vaccinated only against hepatitis B, according to Dr. Jeannette Young, the chief medical officer for Queensland. She called for people to get vaccinated against measles and pointed to the severity of the disease for those who do contract it. "We know that one in three adults who contracts measles will end up in hospital," Young said, Chinese news agency Xinhua reported.

In 2013, 37 people contracted measles in Australia, at the time the biggest outbreak in recent history for the country. Those cases were eventually linked to a traveler from abroad. In March 2014, the World Health Organization declared measles had been eliminated in Australia.