Sydney, Melbourne and Brisbane are the most likely Australian airports to suffer a hit to earnings from a potential global Ebola outbreak.

Credit ratings agency Standard and Poor’s has looked at what would happen if an Ebola epidemic spread beyond west Africa, and diluted demand for international air travel.

Australia’s three busiest airports were rated as a medium-level risk when it came to a potential earnings downturn, along with Hong Kong, Paris and Tokyo, its report says.

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“Simply because the percentage of revenue coming from international passengers is bigger,” report co-author Thomas Jacquot told AAP.

“It’s affecting earnings potentially more. Sydney has a slightly higher earnings impact.”

Adelaide and Perth were regarded as low risk, along with Wellington, Dublin and London’s Heathrow airport, which relies more on travel from other parts of the European Union.

When it came to a possible effect on credit ratings, Sydney, Melbourne and Adelaide were regarded as low risk, alongside Paris, London, Tokyo and Hong Kong.

Brisbane and Perth were seen as medium risk because they are undergoing major capital works, which meant they had less room financially to cope with a drop in international passenger numbers.

“Any impact on earnings, even if moderate, could therefore affect our view on their credit quality,” the report said.

S&P concluded that a temporary drop in international passenger numbers in 2015 would have a limited effect on airports in the Asia-Pacific and Europe.

Its report used the SARS outbreak of 2002 and 2003 as a guide to the consequences for international air travel.

Passenger numbers actually increased in 2004, after the Severe Acute Respiratory Syndrome had spread from China, with passenger traffic at Australian airports rising by 12 per cent, compared with 16 per cent in Tokyo and 26 per cent in Hong Kong.

– AAP