Nic Stevenson, a spokesman for Britain's Civil Aviation Authority, said airlines use filters to try to remove bacteria and viruses from the air passengers breathe.
"These filters are similar to those used in the hospital operating theatres," he said. "The total volume of cabin air is exchanged every two to three minutes compared with every five to ten minutes in most air conditioned buildings."
Chang's team of 80 doctors is on hand to dispense advice on anything from the safety of London's drinking water to getting into a regular sleeping pattern.
"Even before they got off the plane we talk to them about how they can adjust their sleep cycle because it's eight hours for some of them," said Chang. "We tell them to stay up the night before so they can be tired when they get here."
Britain, the host nation, has told its Olympians to avoid shaking hands with officials and to minimize contact with friends and family, according to the country's chief medical officer Ian McCurdie. The 542-member British Olympic Team will use hand foam made by Procter & Gamble's Vicks brand during their stay.
"The greatest threat to performance is illness and injury," he said in a March 6 interview. "The Olympic environment is a hostile one. Housing can be dense, you share rooms and restaurants with many other athletes and there is a lot of extra stress. Most bugs you pick up on your hands, so hand washing is absolutely critical."
— With assistance from Maria Tadeo and Eleanor Lawrie in London.