Anthrax has been found in the body of a 29-year-old Leicestershire drug user who died after taking heroin.
Police and the Health Protection Agency are investigating the death of Tom Forbes, of Loughborough, who died on 26 August.
This is the fourth time anthrax has been detected in a drug user in England since February 2010.
Health officials have urged all heroin users to stop taking the drug and to seek treatment immediately.
Four Loughborough men aged 24, 31, 35 and 37 were arrested in connection with the death but have been released on police bail pending further inquiries.
Leicestershire Police said a post-mortem examination on Mr Forbes was taking place on Tuesday.
Dr Philip Monk, of the East Midlands South unit of the Health Protection Agency, said there was no risk to people who did not take heroin.
"I'd like to reassure people that there is no risk to the general population, including close family members of the deceased."
Tim Davies, deputy director of public health at NHS Leicestershire County and Rutland, said: "While public health investigations are ongoing, it must be assumed that all heroin in Leicestershire carries the risk of anthrax contamination."
He said people should seek medical advice if they experienced signs of infection, such as redness or excessive swelling at or near an injection site, as early antibiotic treatment could be lifesaving.
"This is a very serious infection for drug users and prompt treatment is crucial."
Anthrax is a very rare but serious bacterial infection caused by the organism Bacillus anthracis.
Mr Forbes' family said he was "a happy-go-lucky lad and was always full of fun".
They added he was "first and foremost a dedicated father to [five-year-old] Dylan".
"He was a very considerate and polite man. He kept himself busy by keeping fit which included kick-boxing with his dad, brother and his son."