Just how germy are airplanes? We put one to the test.

On a flight from Cancún to Orlando, I didn't notice any bodily fluids caked on the seat or coursing down the aisle, a relief after several recent incidents involving excretions. But gross organisms are not always visible. Most likely, I was sitting in a pool of germs.With a quick swab test, I confirmed this suspicion."Fail," read the germ-detection device for nine out of 10 high-touch points in the plane's main cabin and lavatories."Stuff that has more human interaction is going to have some level of germs," said Meikel Brewster, executive vice president of Charm Sciences in Massachusetts, which manufactures the rapid diagnostic tests.Airplane cleaning practices are not federally regulated or standardized. The Federal Aviation Administration does not dictate cleaning protocols. The Centers for Disease Control and Prevention offers guidance on how to clean contaminated areas and prevent the spread of disease if a passenger is ill and possibly contagious. Neither agency covers best practices for non-urgent situations, such as when a person sneezes on the seat back, dribbles barbecue sauce on the tray table or rubs their cheek against the window shade.Passenger airlines devise their own sanitation procedures. Delta Air Lines, which last month turned back a plane when a passenger suffered a severe case of diarrhea, said its "clean ambassadors" remove trash, disinfect surfaces and restock lavatories on flights grounded for four hours or less. Its planes receive a deep cleaning overnight. This summer, it cleaned nearly 60 million seats and used 12,500 gallons of disinfectant."We've dedicated even more resources to those efforts with an entire department, Delta's Global Cleanliness Division, which is fully devoted to improving cleanliness across our operation." said Drake X. Castañeda, a Delta spokesman.Other carriers follow a similar regimen. American Airlines, which said it heeds the CDC's recommendations, disinfects high-traffic areas (galleys and lavatories) throughout the day and tackles common touch points (seat belts, tray tables, arm rests) once the plane is tucked in for the night.Southwest said its aircraft maintenance technicians clean, wash and polish the airplanes inside and out and periodically replace the seat covers and aisle rugs. JetBlue cleans interiors, including seating and carpeted areas, during scheduled stops and expands its scope at night to the side walls, coffee pots and tray tables, among other spots.The night-owl schedule benefits early-bird passengers. The rest of us have to fly in a vortex of microorganisms.A preflight swabI learned about the Charm Sciences device from a AAA inspector who uses the kit to gauge the cleanliness of the hotels she examines. Only one test site — a bathroom vanity — failed that day. She granted the property a redo, and it passed.In addition to the hospitality sector, Charm Sciences said several other industries with a high hygienic bar use the machine, such as health-care facilities and food and beverage purveyors.In a 2013 episode of "Bar Rescue," host Jon Taffer swabbed the kitchen of a New Orleans bar called Turtle Bay. He warned the staff that the adenosine triphosphate (ATP) level, which the device reads as relative light units (RLU), should not exceed 2,500. The machine calculated 4 million. After a thorough scrubbing, the number plunged to an acceptable level.A few weeks before my trip, I contacted the company and asked for a loaner. I received the device, which resembled a chunky Game Boy, and three bags containing 25 swabs each.The machine can detect the amount of ATP on the surface (the higher the number, the dirtier the surface) but it can't determine whether the organic matter originated from dead or alive microorganisms or is residual biologic material, such as sweat, skin cells or cookie crumbs.For my practice run, my iPhone registered more than 1 million RLU. I didn't know whether the substance came from my fingertips or my lunch, but there was no question that my device was scientifically disgusting.Planes are petri dishesFew travelers will be surprised to learn that planes are petri dishes. They can also be disease vectors.Stacey Rose, an associate professor of infectious diseases and internal medicine at Baylor College of Medicine in Texas, cited a number of air travel-related outbreaks including tuberculosis, SARS, flu, norovirus, measles and coronavirus."Infectious particles can be spread on an airplane in several ways, such as through inhalation of infectious particles or direct contact with contaminated fluids or surfaces," she said. "The risk of infection depends on things like how contagious the organism is; the type of exposure, including how close the traveler was to the source of infection; and the ventilation of the aircraft cabin."To lower your risk, she recommends hand sanitizer for passengers who are trapped in their seat and can't easily access soap and water. She added that antibacterial wipes can eliminate particles on surfaces and masks can ward off infections caused by respiratory viruses."Good hand hygiene ... is simple and proven again and again to be our best defense against infection - whether in the hospital or on a plane," she said.How I tested for germsAn important disclaimer: This experiment was not scientific. It was a random sampling in an uncontrolled environment. If I moved up or down a row or boarded an earlier or later flight, the results could have been completely different. In addition, I did not wear gloves, and I breathed on my test subjects.That said, I did have a methodology. I focused on seven high-touch points in the main cabin and three spots in the lavatories. I tested each site twice, once in its unadulterated state and again after a swipe with a Clorox wipe.I had a window seat within eye shot of the flight attendant, who was sitting in an exit row jump seat. I swabbed discreetly, but shared my mission with my seat mates, to avoid alarming them with my miniature lab."I thought you were a mystery shopper," the New York-based nurse in the aisle seat said before lowering her eye mask and falling asleep.For the lavatory portion, I divided my tasks between the fore and aft bathrooms. I didn't want to hog the bathroom. At the last minute, I swapped out the entertainment system for the belt buckle, because the seat back did not have a TV screen.Because I wanted an unaltered environment, I didn't inform the airline of the test. And since I didn't engage the company in the experiment, it will remain anonymous.The dirtiest spotsThe winner — or loser, depending on your position — was the lavatory sink handle, which scored the highest reading at 657,689 RLU. The tray table was the runner-up with 427,147."The tray table makes sense because it's getting a lot more use. People put their hands on it. They put their heads on it when they sleep," Brewster said during our debriefing. "You wouldn't want 400,000 on a surface in a hospital."The inside bathroom door handle and belt buckle were next in line for dirtiest at 260,003 and 224,320, respectively. The armrest and seat pocket were a near-tie at 147,574 and 140,547, respectively."The armrest was kind of indicative, as was the seat belt, because you've maybe got human skin cells," she said. "People put their hand on it to raise it up or down, so I would expect that to have some level of ATP."The toilet flusher's number — 35,508 — was surprisingly low considering that everyone (we hope) presses it. Brewster conjectured that maybe the flight attendants or cleaning crew were regularly disinfecting the button. The window shade fell in the same range.The biggest shocker was the safety card in the seat-back pocket. It registered zero ATP. I repeated the test, but the machine flashed the same result: pass, pass, pass."The emergency card obviously doesn't seem like it's been used much," Brewster said.The takeawayThe experiment confirmed what most of us suspect: The tray table is grimy. Even after I wiped it, it still exceeded 32,000 RLU. The bathroom faucet is disgusting, too, and especially troubling. The handle is sabotaging any good hand-washing habits.Based on the results, I'll adjust some of my behaviors on future flights. I will turn off the sink faucet with a paper towel and cover the tray table with a clean material, such as the safety card.