Most people think of foodborne illness outbreaks as spanning a few days or weeks. But, with current technology, disease detectives can find patients of a single outbreak spread across several years and multiple states.
That is the case with an ongoing outbreak of Listeria illnesses linked to fresh peaches that began in 2018. So far, 11 patients have been identified, most recently found in August this year. One of the patients died. Recent recalls of peaches, nectarines, and plums have been initiated while public health officials continue investigating the outbreak.
The links between people sickened in the outbreak this year and the initial patient in 2018 were made possible using whole genome sequencing (WGS). Whole genome sequencing has been likened to fingerprinting used in criminal investigations, but WGS allows the Centers for Disease Control and Prevention to look at millions of pieces of data.
“WGS examines more than 4.5 million ‘letters’ of the genetic code in disease-causing bacteria such as Salmonella. Bacteria closely related by WGS are more likely to have originated from the same source than more distantly related bacteria,” said John Besser, who retired in 2019 as Deputy Chief of the Enteric Diseases Laboratory Branch at the CDC. He continues to work on CDC-related projects through the Association of Public Health Laboratories.
“Ill persons in a WGS cluster will likely have shared exposure, such as a contaminated food product. By focusing on WGS clusters, investigators can detect outbreaks when they are small, even if cases are dispersed over multiple states or widely separated in time.”
