The elderly, frail resident was one of 23 people confirmed to have been infected in aged care homes across the Illawarra Shoalhaven area, South Eastern Sydney region and the ACT.

The NSW Food Authority’s investigation was continuing and test results were yet to determine the cause of the outbreak at homes operated or supplied by IRT, NSW Health said.

‘‘In the affected facilities there have been 23 confirmed cases and it is possible that further patients may test positive as the investigation continues,’’ director of the NSW Health communicable diseases branch Vicky Sheppeard said.

‘‘Nine residents have required hospitalisation and one frail elderly resident with confirmed infection has died,’’ Ms Sheppeard said.

‘‘To our best understanding the salmonella infection was the cause of death of [this] elderly patient in the Illawarra region, who also had several underlying chronic diseases.

‘‘Due to strict privacy regulation we are unable to provide any further information about the patient.’’

Agencies were working closely with a regional food supply company and the aged care facility managers at the affected facilities to identify foods associated with the illness, Ms Sheppeard said.

Food production and catering at the affected facilities had been reviewed by the NSW Food Authority.

"No specific concerns have been identified, but as a precaution and to minimise the risk of further infections in residents, the facilities are no longer serving foods considered as likely risks - for example, food that is not reheated prior to serving."

Ms Sheppeard said patients and their families and carers had been notified of the outbreak and the precautions being taken as part of the continuing investigations.

"There is no evidence of a risk to the wider community. We are focusing our efforts on identifying which food or foods may be carrying the infections so we can prevent further cases in the aged care facility residents."

IRT chief operating officer Craig Hamer confirmed on Thursday that the organisation was still taking admissions at its residential care centres, as it had "taken every possible precaution" to reduce risks to residents.

"NSW Health and the NSW Food Authority are confident that we have done everything we can to ensure their safety," Mr Hamer said.

IRT had taken extra measures to reduce the risk to residents, including reinforcing food hygiene and infection control procedures at all centres and engaging "external specialists to undertake industrial cleaning in our food service areas at affected sites".

Mr Hamer said IRT was working closely with the NSW Food Authority and NSW Health to determine the cause of the infection.

"As a precautionary measure, we have withdrawn all at-risk foods from service at all our care centres. This includes salad products - both fresh and pre-packaged - and cold meats," he said.

A NSW Health spokesperson said the company "continues to withhold from their menu foods that are identified as being of a higher food-safety risk, such as raw salads and fruits, cold meats and frozen products containing meat".

There have been no further reports of illness following the infection period identified by NSW Health as January 18 to February 5.

Last Friday the Illawarra region's public health unit confirmed three elderly residents had been hospitalised due to the outbreak.

Illawarra Shoalhaven Local Health District public health director Curtis Gregory said the elderly residents were mainly suffering from vomiting and diarrhoea, but there were also problems from lack of hydration and some residents had high fevers.

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 by-products - or salad items fertilised by manure.

"It's a fairly uncommon type of salmonella called bovismorbificans and we think it is linked to salad products," Mr Gregory said.

"Specifically we believe it may be due to the fertiliser or cow manure used to grow those salad products."

Cross-contamination can occur when pre-prepared food is cut with a contaminated knife or from the hands of an infected food handler.

Mr Gregory said it was important to note no staff members had become ill, and inspections of the kitchens and food-handling procedures had not found any issues.

IRT have advised residents or family members who have concerns should phone 1800 132 202.

Do you know more?

Email us in confidence at investigations@illawarramercury.com.au