Four people are dead and nearly two dozen were hospitalized — including one person in Nevada — due to a listeria outbreak connected to recalled ready-to-eat products sold nationwide at Walmart, Trader Joe's, Kroger and Albertsons stores, the Centers for Disease Control and Prevention announced .

The Food and Drug Administration initially reported a recall involving prepared pasta meals on Thursday, Sept. 25 , while investigating an outbreak of listeria monocytogenes contamination, which can cause listeriosis and listeria poisoning.

The federal agencies expanded the food safety alert this week, reporting the outbreak is now known to have occurred in 15 states , with a total of 20 confirmed infections as of Sept. 30.

Here's what to know about the updated recall, including which stat

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