"Next time you are at an all-you-can eat buffet, imagine the food displays without any covering: there are flies in the coleslaw, the man in front of you leans over the spread, breathing heavily. His nose scrunches up as though he might sneeze at any moment. You cringe, but it’s too late. Mashed potatoes are off the menu tonight.
"Johnny Garneau is the reason people like this man will never sneeze on your food today.
"On March 10, 1959, the restaurateur and inventor filed his patent for the 'Food Service Table' later known as the “sneeze guard,” meant to protect food on display from bacteria and other germs that may be spread by sneezing. These days, it’s required by law that retail, self-service food bars have one—nary a salad bar shall be left uncovered..."
Go here  for the rest of this article in the Smithsonian magazine.