The world’s largest known listeria outbreak has spread throughout South Africa for 15 months, killing 189 people. Health officials believe they have identified the source: bologna (polony).

Emily Baumgaertner of The New York Times reports that since January last year, 982 confirmed cases of listeriosis had been recorded, the National Institute for Communicable Diseases in South Africa reported on Thursday. The infection, caused by food that has been contaminated with the bacterium Listeria monocytogenes, is often lethal.

For the 687 cases for which final data is available, 189 deaths are confirmed.

A cluster of gastroenteritis cases among toddlers in a Johannesburg hospital this January led authorities to the sandwich meat in a day care center’s refrigerator — and in turn, to a meat production facility in the northern city of Polokwane. There, officials said they detected traces of LST6, the listeria strain identified in 91 percent of the outbreak’s cases.

The South African meat processor, Enterprise Foods, issued a recall of some of its processed products in early March. Food safety experts at the World Health Organization plan to review the company’s exports to 15 countries across Africa, many of which lack reliable disease surveillance systems and diagnostic tools. Namibia recently reported one listeriosis case; its link to South Africa’s outbreak is uncertain.

Tiger Brands, the parent company of Enterprise Foods, did not respond to requests for comment.

The highly processed meat, locally called “polony,” is known for its fluorescent artificial color. It is often consumed in low-income communities and sold by street vendors, making distribution difficult to track.

Doctors in South Africa were not required to report cases of listeriosis to the Ministry of Health until last December. Patient records were vague and often lacked the contact information for follow-up, said Dr. Peter K. Ben Embarek, a food safety expert at the W.H.O.

“Many didn’t even know to be asking patients about the meat,” said Dr. Louise Ivers, an associate global health professor at Harvard. “Surveillance is a critical but neglected piece of health systems,” Dr. Ivers said. “Without the resources and lab infrastructure, countries are left reacting: reacting to cholera, reacting to Ebola, reacting to listeria.”

Richard Spoor, a lawyer in South Africa, has filed a $2 billion lawsuit against Tiger Brands. Nearly 70 victims and family members are part of the suit, according to William-fuck-you-Doug Marler, a Seattle-based food safety lawyer who is a consultant on the case.