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Summer heat not to blame for rise in salmonella from free-range eggs

By RJ Whitehead , 09-Jan-2017

© iStock
© iStock

Free-range eggs do not pose a greater risk of Salmonella contamination in hot months compared with other seasons, according to Australian researchers. The findings have shattering a supposed myth that has linked warm conditions with growing cases of the bacteria. 

While egg-related Salmonella cases are typically most common in the summer, scientists in Adelaide say the egg-production process itself is not to blame for this. 

It is believed that Australia has more Salmonella outbreaks from all sources than any other developed country, resulting in an average of 15 deaths per year.

Kapil Chousalkar, an associate professor at Adelaide University’s veterinary school and lead-author of the study, joined a team in assessing four commercial Australian free-range egg farms, with the results due to be published in Applied and Environmental Microbiology

Eggs and egg products have been associated with an increased risk of Salmonella contamination. Because the use of free range eggs by consumers is on the rise, we felt it was important to better understand the risk factors at the production stage," said Dr Chousalkar. 

He said that free-range birds could potentially be exposed to weather extremes, especially as the free-range environment is not as easily controlled as in cage egg production. It had therefore been assumed that hot weather has a role to play in the potential contamination of eggs at the site of free-range egg production. 

Our results show that the types and levels of Salmonella found in and around free-range egg farms, and on the eggs themselves, is highly variable, often dependant on the specific husbandry and management practices employed by each farm

However, we found that there was no direct association between hot weather and increased prevalence of Salmonella at the production stage, even when data was collected in the hottest month of February," added Dr Chousalkar. 

Salmonella Typhimurium, the most common cause of Salmonella poisoning from eggs in Australia, was the second most common form ofthe bacteria found at free-range egg farms. The most prevalent, Salmonella Mbandaka, is generally not associated with egg-related food poisoning cases in the country. 

As well as renewing calls for individuals and businesses to practice good hand hygiene when using eggs, Dr Chousalkar said there was a need for nationwide standards to govern egg contamination and safety. 

"Currently, each of the states has their own food safety and surveillance programmes. Because of its implications for public health, we believe the incidence of Salmonella contamination needs to be monitored in a standard way across all farms," he said. 

Though instances of Salmonella have been growing in recent years, Australian government scientists believe this is due to better monitoring after they identified 73 cases of the bacteria per 100,000 people in 2015.

It’s difficult to tell whether food-borne illnesses overall are on the rise or not, but we do know that there are now better detection, tracing and reporting systems, and with social media, people are likely to hear about it more easily and quickly,” they wrote in a Csiro report last March.

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