Experts uncertain over source of listeria outbreak

“A widely available common food source” distributed from the Gauteng province could be behind the recent outbreak of listeria, say experts. However, they are not sure what the culprit is.

The bacterial disease, listeriosis, which infects the blood stream and the nervous system, has led to 557 confirmed cases and 39 reported deaths. This was the highest number of reported cases in South Africa’s history, according to the National Institute for Communicable Diseases (NICD).

Typically, only about 80 cases of listeriosis were reported per year. The institute said in Gauteng, the rate of known infections increased from two per million to eight per million. The highest incidence was recorded in the City of Johannesburg at 12 cases per million. Of the 345 cases in Gauteng, over 60% were new-born babies.

Dr Juno Thomas, a pathologist and head of the centre for enteric diseases at the NICD, said the most likely cause was a food source available to everyone – regardless of their social status.

“Because we see cases from both public and the private health sector and the fact that initially we first saw cases in Gauteng predominantly and then in the Western Cape and KZN, this indicates to us the likely burden of exposure was firstly among persons living in Gauteng. It’s more likely that the contaminated foodstuff was distributed further afield, but it originated here,” said Thomas.

Where those infected died, the usual causes were septicaemia or meningitis as a result of infection. The most vulnerable, according to the institute, were pregnant women and people living with HIV.

Of the patients where the HIV status was known, 63% of those infected were also HIV positive. Infants accounted for 37% of the cases.

Helpful tips to prevent contracting potentially fatal disease

Listeriosis is usually spread through the ingestion of contaminated food products most frequently with raw or unpasteurised milk and soft cheeses, but also vegetables, processed foods, ready-to-eat meats and smoked fish products.

The listeria bacterium can survive in normal temperatures associated with refrigeration (4°C). Listeria can also be transmitted from a pregnant woman to her baby during pregnancy or at the time of birth. Direct contact with the organism can cause skin lesions.

Symptoms are usually mild and may include fever, myalgia, malaise and sometimes nausea or diarrhoea. In at-risk patients, spread of infection to the nervous system can cause meningitis, leading to headaches, confusion stiff neck, loss of balance or convulsions.

How to prevent infection Unlike most other food-borne pathogens, listeria can grow in refrigerated foods that are contaminated. To prevent this, it is recommended to have fridge temperatures below 4o C; and freezer temperatures below -18o C.

Therefore, those at high risk of listeriosis should avoid the following foods:

• Raw or unpasteurised milk, or dairy products that contain unpasteurised milk;
• Soft cheeses (eg. feta, goat, Brie);
• Foods from delicatessen counters (eg. prepared salads, cold meats) that have not been heated/reheated adequately;
• Refrigerated pâtés. There is no vaccine for preventing infection. The main preventive measure is good basic hygiene.
• Use only pasteurised dairy products;
• Thoroughly cook raw foods from animal sources;
• Wash hands before preparing food, eating and after going to the toilet;
• Wash raw vegetables and fruits.

– NICD

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