There’s a lot more hitching a ride on Boston’s subway system than meets the eye. Trillions of germs, sloughed off from riders, are smeared across seats, walls, poles, and hanging straps, according to a study from researchers at Harvard’s T.H. Chan School of Public Health released Tuesday.

Coughing and sneezing riders spew oceans of germs. But the researchers were surprised to learn that samples they swabbed from the T’s subways and stations contained few worrisome bugs.

What they collected was no more virulent than what you would be exposed to shaking a person’s hand, said lead author Curtis Huttenhower, an associate professor at Harvard. The least germ-ridden surfaces were vertical metal poles, where bugs have a hard time sticking, Huttenhower said. But fabric seats and straps, and surfaces closest to riders’ faces, were teeming with microbes, according to the study published in the American Society for Microbiology’s journal, mSystems.

Researchers don’t know whether the germs collected were dead or alive. Nor do they know which bugs are more likely to thrive in the transit system, so they’re headed back to the Massachusetts Bay Transportation Authority for more sampling. They hope to identify the normal level of germs on the T, so any spike might offer early clues about a disease outbreak.

“I am very curious,’’ Huttenhower said, “to see if we went back in flu season what we would see on the hand grips.’’

Kay Lazar