Four people who have been under observation in Italy for possible hantavirus infection have all tested negative, the Italian health ministry said on Wednesday.

Tests were conducted on an Argentine tourist hospitalised with pneumonia, a man from the southern Italian region of Calabria who was in voluntary isolation, a British tourist located in Milan and a companion travelling with him.

Tests conducted in hospitals in Rome and Milan came up negative for all four people, the health ministry statement said.

"The risk connected with the virus remains very low in Europe and therefore also in Italy," it added.

The Argentine tourist had left an endemic area in her home country on April 30 and travelled to Italy on a Buenos Aires-Rome flight before later going to Sicily, where she was hospitalised for pneumonia.

The Calabrian man on April 25 had briefly come into contact on a plane with a Dutch woman who later died from the virus.

The British tourist had also come into contact with the Dutch woman on a different flight and was put into quarantine, while his companion was also taken to hospital as a precaution.

Hantavirus is primarily spread by rodents but can be transmitted between people in rare cases, according to the World Health Organization. It usually begins with flu-like symptoms, such as fatigue and fever, one to eight weeks after exposure.

A cluster has been linked in recent days to the MV Hondius ship, which docked in Spain's Canary Islands following a polar expedition that departed from Argentina.

Three people - a Dutch couple and a German national - have died since the start of the outbreak.

The WHO has increased its tally of confirmed cases in the outbreak to nine. It has said further cases could materialise because of the long incubation period, but that this is not a pandemic, and nothing like COVID-19.

-Reporting by Matteo Negri, writing by Gavin Jones, editing by Crispian Balmer/Reuters