New Zealand reassesses Salmonella risk after outbreak

The risk of Salmonella Enteritidis from eggs in New Zealand remains low despite an outbreak, according to the country’s food safety agency.

The original risk profile for Salmonella in and on chicken eggs in New Zealand was published in 2004, with updates in 2011 and 2016. Human illness attributed to New Zealand-grown poultry from Salmonella Enteritidis was not considered. The 2023 update looked at any potential change in the risk of salmonellosis from eggs produced in New Zealand following an outbreak.

New Zealand Food Safety said that while the risk associated with Salmonella Enteritidis is no longer negligible, it is still low. The risk from other Salmonella serotypes also remains low.

Salmonella outbreak

The first reported incidence in domestic, commercial poultry flocks was the detection of a strain of Salmonella Enteritidis through the routine National Microbiological Database monitoring program in March 2021. After detection in a processed poultry carcass, it was also found in hatcheries and poultry sheds of layer and broiler flocks from which the birds associated with the carcass meat detection were originally sourced.

The strain was linked by whole genome sequencing (WGS) to human cases, including an outbreak starting in December 2019, with a higher hospitalization rate than other Salmonella strains.

From 2015 to 2021, there were six salmonellosis outbreaks where eggs were suspected or confirmed as the vehicle of infection, including 79 confirmed and 24 probable cases. From May 2019 to February 2023, one outbreak included 128 confirmed and six epidemiologically linked cases. Of the 134 patients, 49 were hospitalized.

The strain detected in poultry and causing illness in people was phage type (PT) 8, which could have negative consequences for egg farmers, according to the risk profile. The route by which the outbreak strain was introduced into the country’s poultry industry was listed as a knowledge gap.

Early investigations showed inconsistent implementation of poultry industry guidelines, particularly on biosecurity. There was some complacency towards the risk of Salmonella where prevention relied on populating sheds with Salmonella-free birds without sufficient risk management measures throughout the supply chain.

An emergency control scheme was implemented, which led to an amendment to the Animal Products Notice, requiring poultry chain operators to include steps for Salmonella Enteritidis as part of their Risk Management Program. Other measures included testing the poultry environment for Salmonella Enteritidis and changes to overseas market access requirements.

Monitoring the situation

There has been a significant reduction in the export of eggs and egg products from 1,970 tons in 2015 to 1,100 tons in 2022. The amount of egg products imported into New Zealand has almost tripled since 2015, increasing from 346 tons to 983 tons in 2022.

The potential for transmission of Salmonella Enteritidis to eggs via breeder flocks in the supply chain could result in widespread dissemination through the layer poultry chain. Colonization of layer flocks poses a greater risk for consumers. However, absence of reported infections with the outbreak strain since February 2023 suggest risk management actions have been effective.

Vaccination is widely used on New Zealand layer farms and can reduce, but not prevent, flock colonization, shedding, and contamination of eggs. The best approach to gather information on the prevalence of Salmonella on eggs is by environmental sampling of dust and feces in layer sheds.

The current shelf life for New Zealand eggs is 35 days, regardless of storage temperature. However, a reconsideration of these guidelines could happen if the strain were to re-emerge and become endemic in the country’s layer flocks, according to the risk profile.

The risk associated with other serotypes in and on eggs has been unchanged since the 2016 risk profile. This conclusion is based on a low prevalence of non-Enteritidis serotypes in New Zealand layer flocks in a 2016 survey, the static incidence of salmonellosis, and a few outbreaks involving other serotypes where eggs were suspected.

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