Two more West Australians have been diagnosed with Legionnaires' disease after travelling to Bali in the past few months.

This brings the total number of WA travellers found to have the disease to nine, with four more people from other Australian states diagnosed since the start of December.

Department of Health communicable disease control director Paul Armstrong said while the exact source of the disease was not yet known, all but one of the 13 people had stayed at the Ramayana Resort and Spa Hotel in Kuta.

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"The Indonesian Government has been advised of the Australian cases by the Australian Government and is working with the World Health Organisation to investigate the possible source of the disease," Dr Armstrong said.

"The investigating team has taken steps to disinfect potential sources at the hotel, but it's not yet clear this has been successful."

Legionnaires Disease Bali