Inside the hunt for the source of deadly listeriosis outbreak

A rash of purple dots is eating up Gauteng and they stare back at bioinformaticist Mushal Allam every morning as he and his team settle in for another day of fighting one of the worst epidemics South Africa has ever seen.

The DNA of listeria samples is sequenced at Allam’s lab at the National Institute of Communicable Diseases (NICD) and the purple dots on his screen represent each listeria sample that is identified as strain ST6.

ST6, the abbreviation for the innocuously named “sequence type 6”, is currently causing the world’s largest documented outbreak of listeria here in South Africa.

Allam explains the ST6 strain is “virulent”, and particularly good at making humans sick.

What no one knows yet, is why.

Even more urgently, scientists don’t know which food is causing the outbreak.

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