City eateries experienced a staggering 14 percent drop last year in food-borne illness caused by salmonella — the lowest rate in 20 years — as a result of letter grades put in place by the city, Mayor Bloomberg announced today.

The mayor also said 72 percent of inspected restaurants have “A” grades — up from 65 percent in the first six months of the program.

“Clean kitchens are proving to be good for business,” said Bloomberg, who launched the program in July 2010.

A Baruch College study found that 88 percent of New Yorkers use the grading system to decide where to eat.