A decline in Salmonella across Australia in 2020 has been linked to actions to tackle COVID-19, according to a study.

Researchers compared Salmonella rates in 2020 to past years and looked at the impact of COVID-19 measures. Findings were published in the Communicable Diseases Intelligence journal.

To control coronavirus, Australian public health measures included border closures, physical distancing and hygiene advice.

The annual salmonellosis notification rate was 27 percent lower in 2020 than the previous 5-year median. The decline varied throughout Australia. States and territories with more stringent and frequent or longer COVID-19 measures had generally greater reductions. However, Tasmania had a 50 percent bigger reduction than the Northern Territory, despite similar restrictions.

Annual median rates in the Northern Territory are three times that of national data. The persistence of high rates in this state could indicate the importance of demographic and environmental factors, said, researchers.

A peak in notifications in February 2020 was due to a large outbreak across several states. This caused the highest monthly rate since 1991. The outbreak of Salmonella Typhimurium was investigated between January and May.

State differences
Monthly and annual salmonellosis notifications per 100,000 population, for the eight states and territories for 2015 to 2020, were taken from the National Notifiable Diseases Surveillance System.

The five-year median of annual salmonellosis notifications for 2015 to 2019 in Australia was 16,375 while in 2020 there were 12,033 cases.

The lowest monthly rate for 2015 to 2020 was in the Australian Capital Territory in July and October 2020.

From March to December 2020, the monthly rates for all jurisdictions were below the five-year median except in June and September for Western Australia and December for Tasmania.

The rates in South Australia, Victoria, and New South Wales in 2020 showed prolonged low levels. Victoria had the greatest drop and longest plateau coinciding with two COVID-19 lockdowns. A reduced number of restaurant meals and social gatherings where food was produced for many people likely contributed to a reduction in salmonellosis risk, said, researchers.

Smaller decreases for Western Australia, Queensland, and the Northern Territory reflected milder public health steps. It could also suggest the role of a non-foodborne origin of Salmonella with social distancing changes having less of an impact, according to the research.

When such measures eased in June, notification rates did not go down as steeply as the seasonal five-year decrease.

Other factors
Not all people with infection seek medical treatment or get tested but another survey from January to June 2020 by the Australian Bureau of Statistics found no significant decrease in general practitioner service usage.

Changes in laboratory testing priorities likely contributed to the decline in notified salmonellosis cases but are unlikely to have fully accounted for the decrease, said researchers.

Scientists said reduced reports of Salmonella support the importance of behavioral factors in preventing infection.

“Wide-scale application of significant public health measures during COVID-19 appears to have had an impact in reducing infectious diseases including salmonellosis. It is recommended that public health advice continues to promote hand hygiene as this simple intervention has demonstrated to reduce Salmonella transmission,” they said.

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