HOUSTON (AP) — Authorities have traced a multi-state listeria outbreak which has hospitalized four people to a Houston-based Vietnamese food manufacturer.

The U.S. Department of Agriculture said Long Phung Food Products issued a recall for seven types of pork rolls that have been shipped nationwide. They have the number “EST. 13561” inside the USDA mark of inspection. All recalled rolls should be returned or discarded.

READ MORE: Tarrant County Public Health Director Talks With Concerned Moms About Kids, Classrooms And COVID-19

There have been four reported cases of listeria, three of them since Sept. 1. Cases have been reported in Louisiana, Michigan, Texas and Tennessee. No deaths have been reported.

READ MORE: 'Wow, There Goes The Ground': North Texan Wally Funk Shares Story Of Her Dream Journey Into Space

Listeria primarily affects pregnant women, the elderly and others with weakened immune systems. It can cause headache, stiff neck, confusion and convulsions, and in pregnant women can cause miscarriages, stillbirths, premature delivery and other life-threatening conditions for newborns.

MORE NEWS: Texas' Latest COVID-19 Wave Climbing Steeper Than Past Waves, State Health Leaders Say

(© Copyright 2018 The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.)