Biohazards from blood to diarrhea were recently found on planes. What are the chances they will make you sick?

It's fair to assume that you'll come in contact with germs whenever you’re flying. But a recent series of events involving biohazards on commercial flights may leave you wondering what exactly is on or near your airplane seat.

A Delta Air Lines flight bound for Barcelona, Spain, was forced to go back to Atlanta late last week after a passenger had severe diarrhea. “Delta Flight 194 on Sept. 1 from Atlanta to Barcelona returned to Atlanta following an onboard medical issue,” Delta said in a statement to NBC News. “Our teams worked as quickly and as safely as possible to get our customers to their final destinations. We sincerely apologize to our customers for the delay and inconvenience to their travel plans.” (Delta did not respond to Yahoo Life's request for comment.)

Audio posted on LiveATC.net and shared on X (formerly known as Twitter) captured someone, reportedly the pilot, saying, “This is a biohazard issue. We’ve had a passenger who had diarrhea all the way through the airplane, so they want us to come back to Atlanta.”

John Hurdt, who identified himself as a passenger on the plane, said on X that “it was a mess,” adding, “The pilots made the right decision to turn around.”

This isn't the only biohazard situation on a commercial flight recently: Air France passenger Habib Battah told CNN in July that there was a pool of blood under his seat after a passenger on a previous flight had what was described as a “hemorrhage.” He was later told by Air France officials that there were feces in the mix too. “I’ve been covering Beirut for 20 years as a journalist. I’ve lived through wars, airstrikes, seen assassinations, car bombs and narrowly survived the port explosion. I thought I’d seen it all. I didn’t expect to find more blood than I’ve seen in Beirut on an Air France plane,” Battah said.

Then there were the Air Canada passengers flying from Seattle to Montreal who said they found their seats covered in vomit, USA Today reports.

And those are just the recent incidents that made the news.

So what types of biohazards might you find on planes, how are they handled by airlines and what are the chances they’ll make you sick? Here’s what you need to know.

What are the most common biohazards you may see on a plane?

Experts say the biggest ones you may encounter include vomit, diarrhea, urine and blood, typically after a passenger becomes sick or has an injury. However, an airline industry insider (who wished to remain anonymous) tells Yahoo Life that these situations are extremely rare, and notes that the vast majority of flights have no issues.

How likely are they to make you sick?

It depends. “Anytime one encounters a body fluid, there is a chance for pathogen transmission,” infectious disease expert Dr. Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security, tells Yahoo Life. “That is why in health care settings, people wear appropriate personal protective equipment when the chance of contact with body fluids is high.”

On airplanes, it’s unlikely passengers will be wearing gloves, and as a result, there is an infection risk, Adalja says. “Pathogens that could be transmitted include diarrheal pathogens [such as] norovirus and, with blood, HIV, hepatitis B and hepatitis C,” he says. “If someone comes into contact with a body fluid without appropriate personal protective equipment, they should immediately wash that body part with soap and water.”

But Adalja says people shouldn’t panic over this: “Unless a person had exposure through their mouth, their eyes, nose or through broken skin, this is really not a major threat.”

How do airlines handle cleaning the plane in general?

Airlines use specialized cleaning crews between flights, and they’re ready to spring into action when needed, Hannah Walden, communications manager for Airlines for America, tells Yahoo Life. “The health and safety of passengers is the top priority of U.S. airlines, and crews are trained to respond to a range of incidents, including in-flight medical emergencies,” she says.

Biohazard and cleanup specialist Cory Chalmers, president and founder of Steri-Clean, tells Yahoo Life that planes are always cleaned between flights, but procedures have changed slightly since the COVID-19 pandemic. “Prior to COVID, the cleaning between flights was simple — remove trash, run a vacuum and that was about it,” he says. “Once COVID hit, the airline was forced to change their entire marketing strategy to almost solely focus on how they are cleaning their planes.”

Many airlines now add hospital-grade air filtration, which exchanges the air on a plane every few minutes, not just between flights, and also apply disinfectant to all surfaces and use an antimicrobial spray, notes Chalmers.

“Today some of this remains and some of it was phased out, but it honestly varies by airline,” Chalmers says. “I fly exclusively on Delta, so am a lot more familiar with their procedure, which includes removing trash, vacuuming, applying disinfectant through electrostatic guns on high-touch points — seat belts, armrests, tray tables, TV monitors, etc.” (An electrostatic gun, Chalmers explains, is a battery-operated device that delivers a fine mist with a positive electric charge that makes the disinfectant want to bond with surfaces, versus just flying around in the air.)

“Other than that, deep cleaning only occurs about every two to six months when the plane goes in for maintenance,” Chalmers says. “Then it gets a complete deep clean where the interior, exterior and even engines are deep-cleaned.”

How do airlines clean in biohazard situations?

Delta did not respond to Yahoo Life’s request for comment on its cleaning procedures. However, the Daily Mail reports that the plane that turned back due to a passenger’s diarrhea underwent a five-hour cleanup that included replacing the carpet.

Chalmers says planes are usually cleaned as soon as they land on the ground if blood, bodily fluids or other potentially infectious materials are present. “Depending on the size of the ‘spill’ will dictate who cleans it,” Chalmers says. “Most airlines have cleaning crews trained to handle small biohazard spills. However, this is only when the plane is at one of their hubs. If the plane is at a smaller airport, they will either make the seats not available until they can get back to a hub, or have an emergency cleaning performed by an outside company trained to handle such biohazards.”

In most situations, biohazard spills are small and able to be quickly cleaned and disinfected, according to Chalmers.

“The majority of the time, the airline flight crew or ground staff can take care of this with little if any interruption to the flight schedule,” he says. “However, if the incident is a large spill or more complicated in nature due to access, it may not be a quick process. The flight could be delayed or canceled while they wait for professional cleaning companies to arrive or the plane is taken out of service.”