Brown lettuce on sandwich

I ate at shake shack today and 2/3 the way through with my chicken sandwich I noticed the lettuce was brown and wilted. If they service it like this I don’t even know if they wash the lettuce now I’m freaking out and so extremely scared that I contracted listeria. I’m so worried and sad. I’ve been trying my hardest this pregnancy to stay clear of things like this. Will my baby be okay? It wasn’t much lettuce at all but still.