NHS Lanarkshire said it had carried out an investigation into the transmission of hepatitis C to a patient who was in Monklands Hospital in Airdrie.
It concluded that the patient became infected with the blood-borne virus during their inpatient stay, although exactly how this happened remains uncertain.
It comes after it emerged in December that a patient in Edinburgh was infected with hepatitis C while being treated in A&E.
Following the latest case NHS Lanarkshire said, as a precautionary measure, it had written to seven patients and contacted their GPs following their investigation.
These patients were all in Monklands Hospital around the time the patient became infected in April 2012.
But the board said it was “very unlikely” that any of the other patients had been infected with hepatitis C.
NHS Lanarkshire said as a result of its investigation, actions had been put in place to enhance infection control, including increased frequency of checks on the ward environment and additional educational sessions on prevention of infection for staff.
It said new monitoring arrangements had also been used to “ensure a high standard of infection control is being practised on all wards”.
Dr Iain Wallace, NHS Lanarkshire medical director, said: “We are committed to providing the highest standards of infection control across all of our services.
“It is of the greatest regret that on this occasion we did not do so.
“We have already used the lessons learned from this case to make further improvements to our infection control processes and practice.”
Dr John Logan, consultant in public medicine at the board, said: “We have carried out a detailed and thorough investigation.
“While it is very unlikely that anyone else has been infected in connection with this, we have taken the precaution of providing seven patients with information about the situation and a questions and answers document.
“They have also been offered an appointment to see a hepatitis C specialist for further information and advice and to have a test for hepatitis C should they wish to be tested.”
In December, NHS Lothian apologised to a patient believed to have caught hepatitis C in Edinburgh Royal Infirmary’s emergency department.
The board said it was trying to find the source of the infection but believed it was likely to have come from cross-contamination in the A&E unit.
A total of 34 other patients who were in the emergency ward at the same time were contacted by the health board.
Information about hepatitis C is available to members of the public by phoning NHS Inform on the freephone number 0800 22 44 88 or through the NHS inform website nhsinform.co.uk.