The Northern Health Trust board was aware of the Clostridium difficile problem five months before an outbreak was declared, an inquiry has heard.
Trust chairman Jim Stewart said that when it was declared in January 2008, staff morale was low and the board's chief executive under stress.
The inquiry was set up to examine the circumstances surrounding NI's biggest hospital superbug outbreak.
The inquiry has already established that 31 people died from the outbreak .
It is sitting at Antrim Civic Centre and is due to report by the year's end.
The independent panel is reviewing the number of patients who died in Northern Trust hospitals, directly or indirectly as a result of clostridium difficile, between June 2007 and August 2008.
It has heard from bereaved families, former patients and their relatives, as well as Trust staff.
The inquiry has already established that the number of people who died from the outbreak is 31.
Mr Stewart told the panel on Monday that the board was first alerted to an increase in the level of C. Diff in August 2007.
He said that initially figures were low, but then at three separate meetings between October and January, the trust was informed each time that the figures had increased except in November when there was a slight dip.
However, after a meeting in January when the board was told that the number of deaths where C. Diff was considered a factor had increased significantly, the board called an emergency meeting on 7 January and declared an outbreak.
Mr Stewart said a robust action plan was implemented. It included a review of using antibiotics and the introduction of an enhanced cleaning regime.
He said that at the time, the Chief Executive Norma Evans was under considerable stress and that staff morale was very low.
Hospital managers, doctors and the head of communication are due to give evidence to the inquiry which is now entering its third week.