Listeria may not be as common as Salmonella or E.Coli but is lethal. The CDC recommends that any opened pack of sliced meat should be chucked out within 5 days.
Cold meat in the fridge is ideal for the bacterium, Listeria monocytogenes , to reproduce.
Listeria needs urgent medical attention as it can turn life threatening in certain cases.
Source: Medindia