My brother is a Government Health Inspector (thus an expert in this type of thing) and when I asked him about Listeria he emailed me the following...

"If you have to eat cold meats like ham etc, buy the packet ones like Don etc rather than buying it from the deli. Cooking kills any Listeria that may be in foods. Avoid soft cheeses, but again, if you have to, buy them in packages from reputable brands rather than loose from the deli."
This link is very helpful...
http://www.dhs.vic.gov.au/health/ide...eria_facts.htm

(P.S - I am living on egg and lettuce sandwhiches or tinned tuna and salad sandwhiches for lunch)