Seven cases have been related to pregnancy.
In California, one pregnant woman and her twins were sick, and both infants died.
The latest report on the 19-state outbreak noted 2 more cases, 61 total.
The researchers found foodborne pathogens that had formed colonies of pathogens in a sticky biofilm in three common types of plastic in raw and treated wastewater.
Boar's Head has recalled all implicated meat products, but some products have sell-by dates in October 2024
It is now the largest listeriosis outbreak in the US since the 2011 outbreak linked to cantaloupe.
Two states have now found Listeria in unopened liverwurst packages, and genetic sequencing shows a link to the outbreak.
Liverwurst is the main suspect, but investigators are examining if other deli meats are involved in the outbreak.
All measles cases occurred in unvaccinated children.
Sixteen of 18 people sickened (89%) reported eating meats sliced at deli counters (not packaged meats).
