The NHS employs 87,000 in Wales

Nurses, midwives and health visitors are most likely to be the victims.

The Wales Audit Office study found violence and aggression towards health service workers costs �6m a year.

It praised steps taken by the NHS trusts and the assembly government to counter the situation, but said there was still room for improvement.

The Auditor General for Wales, Jeremy Colman, said the problem could be much worse because of under-reporting.

You tend to find mental health nurses take it as part and parcel of the job. It's just an occupational hazard Owain, a mental health nurse

The study, which looked at figures from 2001 to 2004, found the multi-million pound bill for the 15 Welsh NHS trusts is spent on the replacement of staff, training, security and dealing with legal problems.

The report, Protecting NHS Trust Staff from Violence and Aggression, is the first to cover the whole of Wales.

Staff working in mental health, general health and learning disabilities sector also reported being victims of aggression.

The study found one patient threw a fire extinguisher at hospital staff, while another case involved the attempted mugging of a district nurse on a house call.

One nurse, Owain, described how he and a woman colleague were attacked by a patient who pinned them against a window during a night shft.

We are really concerned and we have been lobbying on this issue Tina Donnelly, RCN director (Wales)

"He sort of bloodied my face because he smacked me in the face and the arm. He caught my wedding rings and ripped all my skin. He did the same to my colleague ripped her uniform. We looked like we'd been in a fight on the high street.

"You tend to find mental health nurses take it as part and parcel of the job. It's just an occupational hazard. You may get smacked," he said.

The auditor general said: "The aim of the report was to ask whether the authorities have a grip on the situation.

"The fact that we cannot answer the question (whether violence is increasing) is significant in that respect because there is not a grip on the situation."

He said there was not "sufficiently robust" systems in place in previous years to record incidents.

And he said the "zero tolerance" approach to violence is the right one.

Aggressive behaviour

A new NHS-led Passport Scheme aimed at giving training to staff to cope with violence as well to record any problems has begun.

Tina Donnelly, director of the Royal College of Nursing in Wales, said: "It is very worrying because within the report it is found that nurses, midwives and health visitors are at the front end of violence and aggressive behaviour.

"We would like to see a lot more security measures put in place such as CCTV put in waiting areas so that patients who are aggressive are filmed.

The RCN director said she would like to see assaults on NHS staff treated in the same way as attacks on police.

Nine recommendations are made in the report for the Welsh Assembly Government (WAG) and trusts to follow.