|Date of first report of the outbreak||
12 September 2018
|Disease or outbreak||
Listeriosis, which is caused by the bacteria Listeria monocytogenes serotype 4b Sequence type ST240 (1).
|Origin (country, city, region)||
A national outbreak of listeriosis is linked to the consumption of rockmelon (cantaloupe) originating from New South Wales and affecting other states of Australia, including Victoria, Queensland and Tasmania (2).
|Suspected Source (specify food source, zoonotic or human origin or other)||
Consumption of rockmelons (cantaloupe) from a single grower in New South Wales, the largest State of Australia (3). The grower’s farm is named Rombola Family farms and is based at Nericon near Griffith in regional New South Wales (4).
|Date of outbreak beginning||
Between 17 January and 9 February 2018, 10 elderly people fell sick and were diagnosed with listeriosis (4). The Australian National Focal Point (NFP) notified World Health Organization (WHO) of the listeriosis outbreak on 2 March 2018 (3).
|Date outbreak declared over||
Ongoing cases were documented until 27th July; no cases were reported after that. However, no official announcement has been made regarding the end of the outbreak.
|Affected countries & regions||
|Number of cases (specify at what date if ongoing)||
Up to 27th July 2018, there have been 22 confirmed cases, which comprises of 6 cases in NSW, 8 cases in VIC, 7 cases in QLD and 1 case in TAS (7).
Listeriosis is a life-threatening infection caused by consuming food contaminated with the bacterium L. monocytogenes (8). This disease primarily affects pregnant women and their newborns, older adults, and persons with weakened immune systems (8). The incubation period usually varies from 3 days to 70 days (8).
These symptoms might vary in different cases. In severe cases or cases of invasive listeriosis, patients might develop septicaemia and/or meningitis (9).
In Pregnant women: Infection might cause miscarriage, stillbirth or premature delivery (8).
Other risk groups (Older people and immunocompromised individuals): Additionally, these people might suffer from headache, stiff neck, confusion, loss of balance, and convulsions (8).
|Mode of transmission (dominant mode and other documented modes)||
|Demographics of cases||
Case demographics as of 27 July 2018 (7)
|Case fatality rate||
The case fatality rate as of 27th July 2018 is 31.81 % (7).
For the general population
Additional precautionary measures for individuals at high risk
There is no evidence of acquired immunity and there is no vaccine to prevent listeriosis (12).
There are various preventive strategies followed by the Food Standards Australia New Zealand (FSANZ) to develop national standards for food processing controls and close monitoring is carried out (12).
The standard antibiotic therapy is for 14-21 days and following are the list of medicines for Listeria infection (14):
Mild infection (14)
Severe infection (14)
The treatment and management protocol is almost the same for both pregnant women and people at elevated risk of invasive listeriosis, apart from the fact that foetal surveillance is carried out in case of pregnant women (14).
|Comparison with past outbreaks||
This outbreak is compared below to similar outbreak of listeriosis in Australia in the years 2003, 2009, 2010 & 2014. A comparison is also done with the recent outbreak of listeriosis in South Africa in 2017.
L. monocytogenes exposure in contaminated foods is common in Australia. However, invasive listeriosis is an uncommon disease. From the years 2011-2015 in Australia, the five year mean was 78 cases per year, with a notification rate of 0.3 per 100,000 population (12).
South Africa Outbreak 2017
There were no unusual features identified and the commonly affected people were the immunocompromised and predominantly elderly people (7).
Consequently, onsets of illness were distributed throughout the outbreak period with no obvious clustering at one point in time (7).
All L. monocytogenes positives were further identified as the outbreak WGS strain belonging to MLST240 (7).
During recent years in Australia, the incidence of listeria infection is constant or has slightly declined owing to the collective efforts of the food industry and the government through implementation of standard food safety and hygiene protocols and improvement of the integrity of the cold chain (12). However, there are some shortcomings which have been identified through investigations.
The rockmelons from the Rombola Family Farms (RFF) were sampled by the NSW DPI (NSW Department of Primary Industries) and the whole melons as well as a composite sponge swab tested positive for L. monocytogenes (7). There were also some other peripheral issues noticed in the packing unit of the farms, which included dirty fans (used to reduce the moisture content of melons after washing) and some unclean spongy materials used for packing (7).
Investigations carried out in the rockmelon outbreak indicate that adverse weather conditions (heavy rainfall in December prior to harvest, followed by dust storms) are likely to have significantly increased the organic load and amount of L. monocytogenes present on rockmelons prior to harvest (7).
Food borne outbreaks due to L. monocytogenes that result in product recalls pose an economic burden for a country from the individual and societal perspective (21). Moreover, additional costs are incurred for investigations, ongoing prevention and control activities (21).
Comparative analysis of Australia vs South Africa outbreak
A timely epidemiological and environmental investigation was conducted which resulted in early detection of the outbreak source and early recall, which limited the number of cases in Australia (3). Despite the high number of cases in South Africa, there has been a tremendous delay in the actions taken by the health authorities and the government to trace the source of L. monocytogenes outbreak (22, 23). On the other hand, Australia’s response in rapid identification of the food source, prompt exchange of detailed export information, and genetic sequences through the INFOSAN network helped reduce the public health and trade impact of the outbreak (24).
1. Leclercq A, Chenal-Francisque V, Dieye H, Cantinelli T, Drali R, Brisse S, et al. Characterization of the novel Listeria monocytogenes PCR serogrouping profile IVb-v1. International Journal of Food Microbiology. 2011;147(1):74-7. DOI: https://doi.org/10.1016/j.ijfoodmicro.2011.03.010
2. Victoria State Government. Listeria outbreak linked to rockmelon (cantaloupe) 2018 [cited 2018 1 March]. Available from: https://www2.health.vic.gov.au/about/news-and-events/healthalerts/listeria-outbreak-linked-to-rockmelon-cantaloupe (accessed on 22nd October, 2018).
3. WHO. Listeriosis – Australia 2018 [updated 9 April 2018. Available from: http://www.who.int/csr/don/09-april-2018-listeriosis-australia/en/.
4. ABC News. Rockmelon farm linked to deadly listeria outbreak set to supply melons again 2018 [cited 2018 5 April]. Available from: https://www.abc.net.au/news/2018-04-04/nsw-farm-linked-to-rockmelon-listeria-outbreak-to-produce-again/9617782.
5. NSW Health. Listeriosis alerts 2018 [cited 2018 9 July]. Available from: https://www.health.nsw.gov.au/Infectious/diseases/Pages/listeriosis-outbreak.aspx.
6. Channel News Asia. WHO says Australia exported listeria-tainted melons to nine territories 2018 [cited 2018 9 April]. Available from: https://www.channelnewsasia.com/news/world/listeriosis-listeria-rockmelons-who-australia-exported-tainted-10120888.
7. NSW Government, Department of Primary Industries. Listeria Outbreak Investigation - Summary Report for the Melon Industry 2018 [cited 2018 October]. Available from: http://www.foodauthority.nsw.gov.au/_Documents/foodsafetyandyou/listeria_outbreak_investigation.pdf.
8. CDC. Clinical Features/Signs and Symptoms 2015 [cited 2015 10 June]. Available from: https://www.cdc.gov/listeria/outbreaks/ice-cream-03-15/signs-symptoms.html.
9. NSW Health. Communicable Diseases Factsheet : Listeriosis 2018 [cited 2018 8 October]. Available from: https://www.health.nsw.gov.au/Infectious/factsheets/Factsheets/listeriosis.pdf.
10. Department of Health. Australian Government. Listeria Fact Sheet 2018 [cited 2018 12 July]. Available from: http://www.health.gov.au/internet/main/publishing.nsf/Content/ohp-listeria-fs.htm.
11. Provincial Health Services Authority, BC Centre for Disease Control. Listeria / Listeriosis 2018 [Available from: http://www.bccdc.ca/health-info/diseases-conditions/listeria-listeriosis.
12. NSW Government, Health. Listeriosis control guideline 2017 [cited 2017 1 January]. Available from: https://www.health.nsw.gov.au/Infectious/controlguideline/Pages/listeriosis.aspx.
13. QML Pathology Newsletter. An overview on Listeria monocytogenes 2013 [cited 2013. Available from: http://www.qml.com.au/Portals/0/PDF/Newsletters/QML_NL_2_2013_LR.pdf.
14. Department of Health and Ageing, Government of South Australia. South Australian Perinatal Practice Guideline. Listeria in Pregnancy. 2018 [cited 2018 5 July]. Available from: https://www.sahealth.sa.gov.au/wps/wcm/connect/40111d804ee4eb738f438fd150ce4f37/Listeria+in+pregnancy_PPG_v3_1.pdf?MOD=AJPERES&CACHEID=ROOTWORKSPACE-40111d804ee4eb738f438fd150ce4f37-miGBfa2.
15. Today News. 2 patients in Singapore infected with similar strain of listeria as Australia outbreak. 2018 [cited 2018 16 April]. Available from: https://www.todayonline.com/singapore/2-patients-singapore-infected-similar-strain-listeria-australia-outbreak.
16. NNDSS, Annual Report Working Group. Australia's notifiable disease status, 2014: Annual report of the National Notifiable Diseases Surveillance System. Commun Dis Intell Q Rep. 2016;40(1):E48-145.
17. Oz Food Net. Monitoring the incidence and causes of diseases potentially transmitted by food in Australia: annual report of the OzFoodNet network, 2010. Commun Dis Intell Q Rep. 2012;36(3):E213-41.
18. Popovic I, Heron B, Covacin C. Listeria: an Australian perspective (2001-2010). Foodborne Pathog Dis. 2014;11(6):425-32. DOI: https://doi.org/10.1089/fpd.2013.1697
19. Salama PJ, Embarek PKB, Bagaria J, Fall IS. Learning from listeria: safer food for all. The Lancet. 2018;391(10137):2305-6. DOI: https://doi.org/10.1016/S0140-6736(18)31206-6
20. WHO. Listeriosis – South Africa : Emergencies preparedness, response 2018 [cited 2018 28 March]. Available from: https://www.who.int/csr/don/28-march-2018-listeriosis-south-africa/en/.
21. Thomas MK, Vriezen R, Farber JM, Currie A, Schlech W, Fazil A. Economic Cost of a Listeria monocytogenes Outbreak in Canada, 2008. Foodborne pathogens and disease. 2015;12(12):966-71. DOI: https://doi.org/10.1089/fpd.2015.1965
22. FIRSTPOST. South Africa declares end of Listeria outbreak that affected over 1,000 people 2018 [cited 2018 4 September]. Available from: https://www.firstpost.com/tech/science/south-africa-declares-end-of-listeria-outbreak-that-affected-over-1000-people-5107981.html.
23. Food Technology. Listeriosis — Australia v South Africa experiences 2018 [cited 2018 6 March]. Available from: https://www.foodprocessing.com.au/content/business-solutions/article/listeriosis-australia-v-south-africa-experiences-733326466.
24. FoodNavigator.com. Listeria in south Africa shows cost of under investment in food safety systems 2018 [cited 2018 13 June]. Available from: https://www.foodnavigator.com/Article/2018/06/13/WHO-Trade-bans-must-be-lifted-as-South-Africa-Listeria-outbreak-under-control?utm_source=copyright&utm_medium=OnSite&utm_campaign=copyright.