The number of cases of a potentially fatal superbug in hospitals has shot up.

Managers at Brighton and Sussex University Hospitals NHS Trust can't explain why MRSA cases have risen again after a drop in previous months.

There were 41 reported cases of MRSA at the trust's five hospitals between January and March this year compared to 29 in the three months before.

The news has been branded disappointing and worrying by patient groups and MPs, who are angry the trust appears to be losing the battle to keep infection rates under control.

The trust, which runs the Royal Sussex County Hospital in Brighton and the Princess Royal Hospital in Haywards Heath, already has the highest infection rate in England. Figures released earlier this year revealed the trust had 69 MRSA cases between April and September 2005, a rate of 0.41 per 1,000 bed days.

The Brighton trust aims to have a maximum of 43 MRSA cases a year by 2008.

Chief executive Peter Coles told board members yesterday cutting the numbers was now a top priority and an action plan was being drawn up. It will be unveiled at the next board meeting in June.

Eighteen cases were identified in January, a further ten in February and 13 in March.

Patients affected included those in intensive care who needed a tube inserted or who were on a ventilator.

Others were having dialysis treatment at the renal unit at the Royal Sussex.

Trust director of nursing Alison Robertson said an increase in cases around the winter months was not unusual because of the increase in the number of patients and serious illnesses.

She said: "Patients in places such as the intensive care unit and renal department are also highly dependent and more vulnerable to infection because of the nature of their treatment."

However trusts such as University Hospitals of Leicester Trust, which provides the same specialist services offered by Brighton and Sussex had an infection rate of 0.14 per 1,000 bed days.

The trust has called in infection control experts from Guy's and St Thomas' Hospitals NHS Trust in London who were in a similar position one to two years ago and have now improved their performance. Their advice will form part of the action plan.

Ms Robertson said: "We need to take stock and reset our approach in tackling infection control. We are not complacent about this, we take it extremely seriously."

Mr Coles said: "This is clearly a top priority for us. We will be looking at full proposals on how to deal with this."

Areas likely to be looked at include screening more selected patients for MRSA when they come into hospital and reviewing the staff dress code as research has shown that items of clothing like ties might carry a risk of infection.

Pressure will also be stepped up on doctors, nurses and all staff to remember to always use gels and wipes whenever they enter and leave a ward and when dealing with different patients.

Lewes MP Norman Baker, whose constituency has patients using the trusts hospitals, said he was very disappointed at the latest figures.

He said: "This is a matter of clear public concern and so it is a pity to see the figures going up. I just hope the trust's huge financial problems are not contributing to this."

Janice Kemp from the independent watchdog the Patient and Public Involvement Forum, said: "It is disappointing. At least the trust is now addressing the problem and getting advice on how to deal with it.

"With the help from the London trust hopefully this trust will follow in its footsteps and get the figures down."

A spokesman from the Patient Action Group in Sussex said: "This is not acceptable. Seriously ill patients should be able to go into hospital and not worry about catching another infection.

"The news the figures are getting worse instead of better is disturbing."

Jennie Nicol from Plumpton Green, whose mother Joan died after developing an MRSA infection while at the Princess Royal was appalled at the news.

She said: "They don't seem to be able to get this under control. People are losing loved ones unnecessarily because of this. You hear about all the cuts that are going on in the NHS and this can't be helping."