Of the 18 assaults by patients reported by staff in the second half of 2017, one resulted in a major injury, two in moderate injuries, 10 in minor injuries and five were near-misses.
Mr Cilliers said the incident that resulted in a major injury was under investigation.
"Due to privacy concerns and the incomplete nature of the investigation we are unable to provide further comment."
A Whanganui resident, who did not want to be named, said more security was needed at the hospital to protect the staff and other patients, especially in the intensive care unit (ICU).
The woman spoke to the Chronicle on Friday about an incident she witnessed in August last year while visiting her 84-year-old mother in ICU at the Whanganui Hospital.
"My mother had just had an operation and was hooked up to all these machines when a man arrived who looked like he was on P, he was clearly drugged out and was running around the place scaring all the patients."
She said it was very scary because he was a large man over 6ft tall and could not be controlled.
"There were only two petite female nurses on duty because it was about 7pm and then a security guard arrived but he couldn't handle it so finally the police had to come up."
She said the staff were obviously distressed and all the patients were extremely fearful.
"I felt scared for my mother who had just come out of an operation. There really should have been more security staff available, especially when there is only two small female staff on."
The other injuries that were reported during those six months were 27 counts of staff getting hurt while moving patients, 12 counts of staff that had tripped or fallen, 16 counts of staff unintentionally being exposed to blood or body fluids, and nine counts of staff being bumped into or being struck by an object. The remaining four incidents were not specified.
Mr Cilliers said the WDHB was responsible for the safety of its staff, contractors, visitors and patients.
"Our board and management agree that no business objective will take priority over health and safety.
He said the organisation encourages staff to report incidents and this was reflected in the number of incidents, injuries and near misses that staff do report.
"We believe staff are confident that when they report an incident or issue, it will be investigated and the findings acted upon.
"Key strategies that had been put in place to keep staff safe include training, providing appropriate equipment, reporting, conducting incident reviews, audits, assessments, having appropriate staffing in terms of numbers and skills, escalating incidents, providing a secure environment and rehabilitation including return-to-work programmes."
