© Associated Press
Mark Siler carries some salvageable items from the house of his friend Clay Warden as another storm approaches Joplin
Flying debris from the tornado that tore through Joplin, Missouri, has sparked an outbreak of a potentially fatal infection.

The rare but serious - and in some cases deadly - fungal infection has affected some of the more than 900 people injured in the disaster.

Soil or plant matter on debris that penetrated the skin of some of the people who survived is believed to have caused them to contract an infection called zygomycosis, said Uwe Schmidt, an infectious diseases physician at Freeman Health System in Joplin.

Mr Schmidt said he knows of at least nine patients who have had the infection in the weeks since the disaster.

Three or four of them died and he said zygomycosis was a factor, if not the actual cause.

"It's definitely quite striking," Mr Schmidt said.

"To have so many cases of this is rather rare."

He said he had previously only seen two cases of zygomycosis in his career.

The May 22 tornado cut a six-mile swath through Joplin, killing 151 people while destroying some 6,000 homes and many other buildings.

Several people have been treated for zygomycosis in neighbouring Greene County, said Kendra Williams, administrator of community health and epidemiology for the Springfield-Greene County Health Department.

"It's just an unfortunate side effect of the tornado," Ms Williams said.

"You deal with the sadness and emotions from the tornado itself and then you find there are problems associated with this."

Symptoms of pain, swelling and skin discolouration typically showed up about five to 10 days after the tornado.

But depending on a person's age, health and wounds suffered, some cases could still surface.

The infection can spread rapidly and invades the blood supply.

Treatment is with intravenous anti-fungal mediation and removal of damaged skin tissue. Mold can be seen in some of the wounds, Mr Schmidt explained.

Public health departments in the Joplin region have notified doctors and hospitals to be aware of the possible infection when treating patients injured in the tornado.