I noticed that the tamales those guys sell are always warm. The tamale man carrys the tamales in an ice chest. I asked how they do it. I was told that they fill the ice chest with hot water before they put the tamales in. They pour out the hot water, put the tamales in, then they put cloth soaked in hot water around the tamales. I guess that I am lucky I have never gotten sick from eating that stuff.
Most caterers do the exact same. If the tamales are above 140F (and that's easy to do in an Igloo) or they haven't been in the danger zone (42F-140F) for more than 4 hours, you are generally safe.
I would worry more about washed hands. Shigella is ugly.
/johnny