NSW and Victoria have recorded six cases, there are four in Queensland and one in Tasmania. There have been two deaths in NSW and two in Victoria.
Rockmelon (cantaloupe) came from Rombola Family Farms based in Nericon, in southwest NSW, according to authorities. The company ceased production after being notified of a potential link to illness.
NSW Food Authority said pending the outcome of its investigation there may be additional regulatory actions or oversight on the rockmelon industry to drive compliance and improve food safety.
Long incubation period
Dr Vicky Sheppeard, director communicable diseases NSW Health, said cases became ill before the contaminated rockmelons were recalled on 28 February.
“Listeriosis has a long incubation period - up to 70 days. Therefore there are multiple foods consumed and retailers used by the cases, which need to be thoroughly investigated and the findings matched to specialist laboratory test results, to determine the source.
“All state and national guidelines have been followed and public warnings issued here and interstate when the food source was identified. Typically around one third of people who fall ill with listeriosis die every year. Most of the cases are never related to an outbreak like this one we’re seeing with the rockmelon contamination.”
Food Standards Australia New Zealand (FSANZ) co-ordinated a recall of whole rockmelons.
Authorities said rockmelons on shelves are not implicated in the outbreak. However, consumers have been urged to dispose of fruit purchased between the start of January and 1 March, because it is difficult to determine its origin.
Dianne Fullelove, industry development manager at the Australian Melon Association, said: “The most likely source of the contamination is rockmelons from one farm who voluntarily withdrew fruit…as soon as the situation was known. Other types of melons are not implicated.”
Listeriosis is rare in Australia with an average of 77 notified cases per year over the past 10 years compared with 13,331 cases of Salmonella.
There has been a significant increase in listeriosis in January and February with 30 cases compared with 71 for 2017, according to the Food Safety Information Council.
Singapore and Hong Kong affected
The Agri-Food & Veterinary Authority (AVA) of Singapore is recalling all rockmelons from Australia pending clarification on their source.
It has taken samples of locally sold rockmelons for tests with results pending. There have been no cases of listeriosis linked to the fruit in the country.
Rockmelons were imported into Hong Kong by Wing Kee Produce Limited, ETAK International Ltd., Wing Hong Woo and Ming Kee Chan Co., Ltd. between 1 January and 28 February.
Luen Woo Loong Limited, Calfruits Company Limited, Wellcome Company Limited, Sun Lee Laan Wholesale Food Limited and Good View Fruits Company Limited also imported rockmelons.
All nine firms confirmed product had sold out.
The Centre for Food Safety (CFS) has not received reports about listeriosis caused by rockmelons in the past two months.
MPI confirmed with Australian colleagues that product had not been imported to New Zealand.
Ensuring rockmelon safety
Dr Chris Derry, senior lecturer and principal research supervisor at Western Sydney University, said those who work with food must practice handwashing after using the toilet or working in the garden and again before handling food.
“This may be neglected on food farms, where safe handwashing facilities are far from fields, and where untrained labour is hired for picking operations. Removing adhering dirt is essential when fruit and vegetables are processed.
“Rockmelon presents a thin, low acid, matt skin which is both good collector and poor barrier to dirt and bacteria. Nevertheless, contamination at sufficient level to cause an outbreak could be considered to indicate a serious lapse in irrigation, handling or storage hygiene."
Professor Enzo Palombo, acting dean in the school of science at Swinburne University of Technology, said ready-to-eat foods are often linked to outbreaks because they are not processed further.
“The current incident has been linked to bacteria found on the skin, not the flesh, of rockmelons. However, the risk is that the bacteria can be transferred to the flesh during preparation (cutting and slicing). Storing whole or cut fruit in the fridge does not eliminate the risk as Listeria bacteria survive and grow at low temperatures.
“A similar outbreak in 2011 in the US resulted in 146 cases and 30 deaths across 28 states.”