For the small, insular world of triathlon, it has been a week.

Last Monday, the International Testing Agency announced that Collin Chartier, a top American triathlete who had something of a breakout season last year, had tested positive for erythropoietin, commonly known as EPO, a performance-enhancing substance that has long been a favorite among endurance athletes.

EPO stimulates the production of red blood cells, which helps the body transport oxygen, ultimately increasing stamina. For years in professional cycling, it was about as common as saddle sores. Also, after more than two decades of doping scandals in nearly every sport, from track and field to baseball, most athletes, sports officials and fans have come to react to the latest positive test in the manner of Captain Renault entering Rick’s Cafe in “Casablanca.”

“I’m shocked! Shocked to find that gambling is going on in here.”

And yet Chartier’s positive test, his acceptance of a three-year suspension from competition and his subsequent attempts — on one of the sport’s leading podcasts and on social media — to own the violation, have rocked triathlon, producing the kind of shock and outrage over doping that recall a more innocent era.

“It’s really blown up the sport,” said Dan Plews, who coaches several elite triathletes, including Chelsea Sodaro, the reigning Ironman world champion.