An elderly woman has died after contracting a superbug at Lincoln County Hospital, her family claims.
Kathleen Fletcher, 81, who died on Thursday, was admitted to the hospital six weeks ago with a severe bladder infection.
Her family told BBC News her death certificate named clostridium difficile (C Diff) as a contributing factor.
The trust said no-one has died as a direct result of C Diff during a recent outbreak of the bug.
"We're taking all necessary measures to contain the outbreak and to eliminate the infection by making sure antibiotics are used judiciously and by isolating the relevant patients," a statement from United Lincolnshire Hospitals NHS Trust said.
The trust said one ward had been closed as a precaution.
A second ward at the hospital was also shut because of a separate outbreak of a more common winter sickness virus.
Officials said about 10 people were being treated for clostridium.
Chief nurse Sylvia Knight said: "It (C Diff) affects the elderly and the very sick because the antibiotics they are prescribed for their underlying condition can kill off the body's natural resistance making them vulnerable to this particular infection."
She added the trust's rates for C Diff had been among the best in the country for the past two years.
"If someone dies the death certificate records what they died with and what they died of.
"So even if Clostridium Difficile is noted on the death certificate it does not mean it was the cause of death," Mrs Knight said.