A resident at an Illawarra IRT home has died and nine others have been hospitalised since the outbreak of the unusual strain.

There have been 23 confirmed cases between January 18 and February 5, and health officials say more  patients may test positive as investigations continue.

On Friday night,  IRT chief executive Nieves Murray said the NSW Food Authority had conducted rigorous scientific testing at the affected care centres and IRT Catering  in  the past two weeks and had confirmed ‘‘there was no evidence of salmonella at any of our sites and that adequate controls are in place to ensure the safety of our residents’’.

Ms Murray said her expert team was working around the clock, monitoring  any gastroenteritis-like symptoms at IRC care centres associated with the bacterial infection.

She urged anyone with symptoms to come forward so authorities could identify the cause as soon as possible.

 Reports suggested three staff members at a Wollongong IRT  centre had fallen ill but Ms Murray said there had been no confirmed cases involving IRT staff.

‘‘We are certainly encouraging residents or carers and staff to talk to their area manager about specifics at their care centres, so the more they report through the channels of the organisation,  the more quickly we are able to get onto the investigations so that we can assist the NSW Food Authority and the NSW Health Authority,’’ Ms Murray said.

‘‘We are encouraging our staff to raise it with their manager and activate our escalation processes.

‘‘We are not aware of any cases among staff and we’ve certainly asked staff who have called in sick if they have gastro symptoms to seek treatment.’’

IRT quality and systems review adviser Reuben Sakey said it was important that staff with symptoms co-operated quickly in the interim period before they got any pathology results ‘‘to assist in identifying commonalities’’.

Salmonellosis is one of the most common notifiable conditions in NSW, with more than 3000 people diagnosed each year and many going undiagnosed.

The bacteria is mainly spread to people when they eat undercooked food made from infected animals – including meat, poultry, eggs and their byproducts – or salad items fertilised by manure.

Identifying the source was complicated  because IRT sourced products from suppliers in the Illawarra and across Australia.

‘‘There’s a multitude of scientific investigations happening to identify a smoking gun if you like, finding evidence of an infection in food or in the environment,’’ Mr Sakey said.

‘‘So far all of that has been negative, 100per cent.

‘‘To identify commonalities against food histories,  it’s an analytical process of elimination and in the absence of positive evidence, what it comes down to is the best possible reasoning,’’ he said.

‘‘Every test done at every site is 100per cent negative and that keeps us going further down the rabbit burrow.’’

IRT had carried out a range of professional, deep cleaning processes at all sites and brought in a separate contractor to ‘‘be 100per cent satisfied there was someone overseeing that work purely for an independent point of view’’, Mr Sakey said.

‘‘The remaining products that come through food suppliers, [come from a] combination of local and nationwide commercial distributors across Australia.’’

Mr Sakey said NSW Health was looking at commonalities in food histories to try to ‘‘triangulate suppliers versus menu versus consumption’’.

‘‘That is the most difficult element, we are often dealing with people who are aged and frail and have poor recall.’’

Mr Sakey said IRT had implemented an increased level of monitoring of food consumption in high-risk areas.

IRT has advised residents or family members who have concerns to phone 1800132202.