Parents like to joke that their children’s classrooms are nothing more than petri dishes with desks. But it’s not just schools that are perfect breeding grounds for the flu.

Office spaces are perfect incubators for illness, what with so many people touching commonly used surfaces and the lack of fresh air.

Surprisingly, the main culprit is not people sneezing without covering their mouths (although it certainly doesn’t help).

Charles Gerba, professor of microbiology and environmental sciences at the University of Arizona, led a study of how germs get passed around at work and found viruses move quickly from people touching and infecting commonly shared items.

“We put harmless viruses on certain participants’ hands in an office. Within four hours, they had spread to half the other workers’ hands and half the commonly touched surfaces. We were surprised how fast they move.

“If you sneeze in your office, only the surrounding office air gets contaminated. But if you touch the virus, you move it around the building,” Gerba said.

Most cold and flu viruses can last about two to three days on surfaces; stomach viruses can last up to 30 days, Gerba said.

With flu season upon us, it’s important to know where are the germs lurking in the office:

- 75 percent of break-room faucet handles;

- 48 percent of microwave handles:

- 27 percent of keyboards;

- 26 percent of refrigerator handles;

- 23 percent of water fountain buttons;

- 21 percent of vending machine buttons