The death count in South Africa’s listeriosis outbreak — the worst documented outbreak from Listeria monocytogenes in global history — has topped 100.

The National Institute of Communicable Diseases (NICD) reported this week that the number of confirmed listeriosis cases is now 852‚ and 107 people have died. The death rate, based on the outcome data for 355 cases for which details are available, sits at 30 percent, according to the South African news website Times LIVE.

Of the 852 confirmed cases‚ 42 percent were babies younger than 1 month. Pregnant women are 20 times more likely to develop listeriosis infections than other healthy adults. Women account for 55 percent of the reported cases in which gender is known.

Listeriosis comes from eating or drinking food or beverages containing the pathogen Listeria monocytogenes. The bacterium is found in the environment in water, soil, vegetation and in certain animal feces, including those of infected people. It can contaminate animal products, including meat and dairy, seafood and fresh produce. Once Listeria becomes established in a food production facility it can be very difficult to remove.

The source of the South Africa outbreak that started in January 2017 is thought to be a food product or range of products from one company, but that is still just a theory. Victims include people from various social and economic backgrounds.

Fifty-nine percent of the cases have been reported in Gauteng‚ with 13 percent in the Western Cape and 7 percent in KwaZulu-Natal.

Pretoria-based food safety expert Dr. Lucia Anelich told Times LIVE that the likely culprit is a product consumed extremely often by consumers across the country. That could be ready-to-eat foods that consumers don’t cook or heat, including deli meats.

Listeriosis symptoms — typically flu-like — generally develop between two and 30 days after eating food contaminated with Listeria. But the incubation period can be as long as 70 days after exposure, complicating the investigation because it’s harder for people to recall possible food sources.

Municipal environmental health practitioners in all provinces are systematically inspecting and taking samples at food production‚ processing and packaging facilities.

The DNA of Listeria monocytogenes samples sequenced at the National Institute of Communicable Diseases identifies the virulent strain as ST6, or sequence type 6.

While pregnant women are at high risk of developing listeria, they often do not have symptoms. They can pass the infection to their children during pregnancy or labor.

Globally, listeriosis outbreaks have been caused by contaminated cantaloupe, ice cream, sausages, corned beef, tongue, ham and other processed meats, soft cheese, corn, mussels, salmon, chicken, eggs, pasteurized and unpasteurized milk, spinach, lettuce, butter and prepared fruit salad.

South Africa’s Health Department asked the SA Meat Producers Association and the Red Meat Industry Forum in December to tell their members who make processed food to provide samples of tested food or lab results looking for Listeria monocytogenes in processed meat, but neither complied with the request, according to Times LIVE.

Before the South African situation, the world’s largest listeriosis outbreaks were in the United States in 2011 and in Italy in 1997.

The Italian outbreak was traced to cold corn and tuna salad. It sickened more than 1,500 people, mostly children at two elementary schools. Public health officials traced the 2011 U.S. outbreak to cantaloupes from Jensen Farms in Colorado. In that outbreak, 147 people across 28 states were sickened and at least 33 people died.

Other Listeria outbreaks have resulted in fatality rates as high as 20 to 40 percent. The best known of those was the high-profile Listeria outbreak linked to deli meats from Canada’s Maple Leaf Foods, which caused the deaths of 22 mostly elderly Canadians.

As in the United States, listeriosis is a reportable disease in South Africa, meaning every patient with the diagnosis must be reported to federal health authorities. However, it’s possible some cases have not yet been diagnosed and reported in South Africa because of the long incubation time and the lag time between initial diagnosis and notification of government health officials.

Until the outbreak ends, South Africans are being urged to wash always their hands before and during food preparation and before eating. Health officials are also reminding the public of the importance of separating raw meat, poultry and seafood from other foods and to cook meat, poultry, eggs and seafood thoroughly. Consumption of unpasteurized, raw milk and products made from it is also being discouraged.

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