More than a decade ago, city health inspectors would see occasional mouse droppings at Philadelphia International Airport, black residue and slime inside ice machines, and eggs and other cold foods kept at temperatures too warm.

In 2011, the airport approved the hiring of two former city health inspectors, and the results have been dramatic.

Violations for risk factors known to cause food-borne illness have significantly declined. Today, the airport’s 27 eat-in restaurants have a better average than the citywide numbers for 5,000 non-airport eat-in restaurants.

The airport numbers improved after MarketPlace Philadelphia, the company that manages the airport shops and restaurants, hired Ken Gruen, a retired health department district supervisor in West Philadelphia, and Jerry Zager, another health inspector, who worked with Gruen.

The two have a business, Environmental Health Consultants L.L.C. In addition to making sure 70 food establishments between Terminals A and F are up to snuff, their other major client is the Philadelphia Four Seasons Hotel. “We inspect the kitchen, their entire food preparation and storage facility,” Gruen said.

At the airport, Gruen and Zager make the rounds of every terminal once a month, checking food-storage temperatures, cleanliness of floors and countertops, whether there are paper towels, hot water, and soap, and whether the establishment has a current city food license. They also make sure there is a certified food-safety handler on duty, as required by the Philadelphia Health Code.