More eggs have been recalled in Australia as authorities continue to investigate a Salmonella outbreak.

Synergy Produce Pty Ltd recalled Southern Highland Organic Eggs 300-gram (six-pack) and 700-gram (12 pack) sold at Woolworths in New South Wales and Australian Capital Territory, IGA in NSW and independent retailers in that state.

The recall is due to potential microbial Salmonella Enteritidis contamination in the eggs that have best before dates up to and including May 9, 2019. Unlike in other countries, this strain of Salmonella is not endemic in Australia.

In a statement, Synergy Produce Pty Ltd said a test for Salmonella returned positive and urged consumers not use implicated products but to return them to the point of purchase to ask for a refund.

Authorities are continuing to investigate the outbreak linked to eggs. Confirmed cases have been reported in NSW, Victoria, Queensland, and Tasmania with the only increase noted in New South Wales since the last recall.

Victorian health authorities recorded five cases possibly part of the outbreak, there is one in Tasmania and 167 people in NSW have become unwell with the outbreak strain since it was first reported in May 2018.

The strain has also been detected on chicken farms in NSW and one farm in Victoria.

Food Standards Australia New Zealand (FSANZ) is coordinating recalls that date back to September last year.

In September 2018, Glendenning Farms issued a recall while Bridgewater Poultry Eggs and Ash and Son Eggs took action in March this year.

Australia continues to have some of the safest eggs in the world. They should always be cooked until the white is completely formed and the yolk begins to thicken, according to Australian Eggs Limited.

People infected with Salmonella commonly develop a headache, fever, stomach cramps, diarrhea, nausea, and vomiting. Symptoms often start six to 72 hours after infection and usually last for four to seven days.