Chris Horner. Bryn Lennon/Getty Images

Chris Horner, one of the most accomplished riders in American cycling, has revealed to Business Insider that he's been battling a superbug that could force him to end his racing career.

The bug is called Pseudomonas aeruginosa, and Horner said it seriously affects his lungs during competition. The condition "feels like asthma," he said, but emphasized it isn't actually asthma.

Pseudomonas infection is caused by strains of bacteria found widely in the environment, according to the Centers for Disease Control and Prevention. The CDC says that while serious infections usually occur in people in the hospital or with weakened immune systems, healthy people can also develop mild illnesses. Pseudomonas infections are generally treated with antibiotics.

"I knew there was some kind of bug down there, and they finally found it at the end of October," Horner said by phone from his home in Oregon this week. "I did eight rounds of antibiotics and just finished my ninth.

"But of course each round has been different, and it's stronger antibiotics each time," he added. "Before this last round, they didn't know what they were trying to kill, so hopefully now that they've done the bronchoscopy, they know exactly what they're trying to kill.

"Every doctor I talk to says, 'You're on the right path — you just gotta wait it out,'" Horner said. "So I'm trying to keep the head in a good place, but if the season starts and I got a bug in the lungs, maybe I move on to something else."

Superbugs — bacteria that are resistant to antibiotics — have been around for decades, but they are getting increasingly harder to treat.

One of the chief drivers of the resistant bugs is our zealous overprescription of antibiotics. Doctors prescribe the drugs for ailments that they don't even treat and farmers put them in animal feed. The problem is global.

Pseudomonas aeruginosa. CDC

"Long term it seems like the body will eventually take care of it, but I won't be able to race comfortably until it is gone," Horner added. "But no risk beyond racing issues for me.

"We'll see if the latest round of antibiotics works its magic in the coming weeks," he added. "I'd love to see how long I could race my bike for.

"I mean, I'm 45 next year. In cycling, most riders are done at by 34, a few go 35, and 36 is old. So when you're going 44 like I was this year, that's eight years past the expiration date."

It was at the 2014 Tour de France that Horner believes he picked up the bug, he said, and it has affected his performance on the bike ever since.

"I'm thinking it was picked up on the cobblestone day [stage 5] when it rained and we were racing across the cobbles," he said. "But it's a guess. No one could tell you. It's like if you get a cold and they're like, where'd you get it? I can only tell you the period of time it was picked up, July 2014. Then again, maybe I got sick because I was sleeping on the wrong pillow.

Chris Horner shared his most recent lab results with Business Insider. Courtesy of Chris Horner

"At first it started off with Z-Pak, which works for common colds or something like that," he said. "It got more intensive, and I ended up with ciprofloxacin, which is basically a super-strong antibiotic that hopefully kills it off, but this is sort of the last three-week dose of ciprofloxacin. We'll see if it works. Whatever the bug is, it's really antibiotically distant, so they've had an incredibly difficult time trying to kill it."

Z-Pak, a commonly prescribed antibiotic, does nothing for the common cold, which is caused by a virus known as rhinovirus. In the US, some 60% of people brought to doctor's offices and emergency rooms by sore throats — one of the tell-tale symptoms of common colds and the flu, both of which are caused by viruses — walk out with prescriptions for antibiotics, which kill bacteria, one long-term study found.

Horner is 44 years old, and for the past several years, when healthy, he ranked among the finest climbers in world cycling, and the US's top stage racer.

In 2013 he won the mountainous Vuelta a España, or Tour of Spain, becoming the first American to win the race.

With his Vuelta title Horner became one of three Americans to win a grand tour, or three-week stage race. Greg LeMond claimed three Tour de France titles, and Andy Hampsten won the Giro d'Italia, or Tour of Italy.

Horner has finished as high as ninth at the Tour, in 2010. Remarkably, even with the superbug, Horner managed to finish 17th in the 2014 Tour. But he said he was "suffering and swinging off the back the whole time."

Chris Horner is the only American to win the Vuelta a España, or Tour of Spain. AP Photo/Paul White

He raced on Team USA at the London Olympics and has won some of cycling's most prestigious races, including the Amgen Tour of California and the Vuelta al Pais Vasco, or Tour of the Basque Country. Before he started racing full time in Europe he won most of the US's major races, including the Tour de Georgia and the San Francisco Grand Prix.

He said he's hopeful that he will start the 2016 racing season.

"If I can get healthy I'm gonna race my bike — if I can't, then I'm going to find something else to do," he said. "It's difficult, because it's not like a broken bone. If the doctors can fix it with antibiotics and the lungs go back to normal, and I have the same kind of legs I had this year at the Tour of Utah, then I'm going to race my bike and win a bunch of races. But if they can't, maybe I call it a career.

Horner won the Amgen Tour of California in 2011. Doug Pensinger/Getty Images

"I had amazing legs at Utah, just amazing. They were never hurting, I was never in pain. I just couldn't breathe. It feels like asthma, but it's not asthma. The harder I race, the more I exert myself and the more it affects the lungs and causes the lungs to just collapse. It's the same effect as having an allergic reaction that asthma gives you."

This off-season he's staying fit and riding his bike in moderation as his lungs recover, he said.

Chris Horner celebrates after winning the sixth stage of the Tour de Suisse, from Buerglen to Arosa, Switzerland, June 16, 2005. AP Photo/Keystone, Juerg Mueller

Horner's current team contract, with Airgas-Safeway, ends December 31. Whether he would return to the team depends in part on the team's makeup, he said. "If not, I'll just start racing my bike and race for fun," he said.

Asked what his "gut feeling" was regarding his chances of racing professionally in 2016, Horner said: "That I start the season? Really high. That I finish the season? I don't know."

He added that he isn't sure what he'd do if he retired, but it would more than likely be cycling-related.

Erin Brodwin contributed reporting.