In the last month, nine people have died and dozens have been hospitalized in a listeria outbreak linked to Boar’s Head deli meats that has led to a recall of seven million pounds of its products.

The outbreak has been traced back to a Boar’s Head plant in Jarratt, Va., where federal inspectors had documented repeated problems. The inspections records show that they found black mold, water dripping over meat and dead flies.

The plant has been temporarily shut down in the wake of the outbreak. But reports of illnesses and deaths have continued to accumulate, prompting public health officials to issue more warnings to consumers to ensure they discard certain Boar’s Head lunch meats that may still be in their refrigerators.

Here’s what you should know.

What is listeria?

Listeria monocytogenes is a bacteria that can be deadly. The largely food-borne Listeria illness can be contracted through foods like contaminated deli meats and unpasteurized milk products, according to the Mayo Clinic.

People may also fall ill by touching a listeria-laden surface before touching their mouths.

Federal public health experts said the Boar’s Head case was the worst listeria outbreak since 2011, when tainted cantaloupe killed 33 people and hospitalized at least 143.

Anyone can become sick from the bacteria, but it is most likely to cause severe illness in pregnant women, adults older than 65 and people with weakened immune systems.