A hospital in Cornwall has denied it tried to cover up the fact a patient had died from clostridium difficile.
Jim Roan was undergoing cancer treatment
The allegation was made by the widow of a man who contracted the bacterium at the Royal Cornwall Hospital in Truro.
Jim Roan, 50, was being treated for prostate cancer and pneumonia but his wife Jill said the death certificate mentioned only the prostate cancer.
A second certificate was issued, but the hospital has insisted the correct procedures were followed.
It has offered a verbal apology to the family for not properly explaining the situation.
Mrs Roan said when she questioned the cause of death on the original certificate the hospital contacted the coroner, who ordered a post-mortem examination.
An independent pathologist confirmed C. difficile as the main cause of death.
Mrs Roan believes the hospital was trying to mask the role of the infection.
She told BBC News: "As far as we're concerned, not only did Jim pick up C. difficile from the hospital while he was there, but it was this horrific cover up job and the hospital won't admit to anything."
Mr Roan, who was a chef, was told by an oncologist in 2005 that his condition was terminal and he had about two to three years to live.
"We accepted that," Mrs Road said. "But that's not what killed him - it was the C. diff and the hospital knew that.
"I don't even know who signed the first certificate because the hospital won't tell us anything."
Mrs Roan said she is seeking legal advice.
But the Royal Cornwall Hospitals Trust's medical director, Dr Rob Pitcher, said the correct procedures were followed.
He said the initial cause of death was written by a doctor and it had been necessary for a coroner to legally change the document.
"Death certificates are the responsibility of the doctors filling them out and they have to apply their clinical judgement.
"Obviously in this case, there was a discussion with the relatives and they were unhappy with what was on the death certificate.
"It is a legal document and we can't alter it ourselves in the hospital."
C. difficile is more dangerous to frail and elderly patients
The second certificate states C. difficile as the primary cause of death, with pneumonia and the prostate cancer as contributory causes.
Dr Pitcher has offered Mrs Roan and her family an apology for the lack of information.
"I'm really sorry about that. Obviously they haven't had an adequate explanation of what happened around the death and the death certificate."
The trust said all cases of C. difficile have to be reported centrally and form part of the national statistics.
Recent data published by the Health Protection Agency showed about 7,000 inpatients had MRSA infections each year in England, whereas more than 50,000 inpatients aged 65 years and over had C. difficile infections.
The symptoms are usually mild, involving diarrhoea and stomach pains. But in severe cases it can cause inflammation of the bowel which can be life-threatening.