THE DAY BEFORE the Celtics opened training camp, a nurse peered up at Shaq and delicately swirled a cotton swab inside each of his ample nostrils. The purpose was to determine the threat he posed to his new club. You'd think the team would have sussed that out before signing the 18-year vet, but this mission wasn't about the possibility of the NBA's oldest and beefiest jester undermining the game plan or locker room chemistry. No, this was about Shaq infecting the Celtics literally, with an invisible intruder that could turn Delonte West's big toe into a pus-filled plum or Paul Pierce's middle finger into an inflamed sausage or his elbow into an angry grapefruit.

All of which happened four years ago, hospitalization and surgeries included. As disturbing as it all was, the situation could have been far, far worse, so the Celtics want, at all costs, to avoid a repeat. Hence, the Q-tips up the nose. "We still don't know where it came from," says trainer Ed Lacerte. But at least they now know what "it" is.

The proper name is Staphylococcus aureus, but like Shaquille O'Neal himself, its Q-rating allows for informality: staph. Unlike Shaq, though, there's nothing funny about staph, a bacteria that's harmless until it finds a break in the skin; even a paper cut -- Pierce's finger injury -- will do. After that, all bets are off. In the States, staph has put more people in the hospital than swine flu, and once in the bloodstream, its scariest version can be deadlier than HIV.

For a while, beginning in the late '50s, the development of penicillin's synthetic cousin, methicillin, provided a quick remedy. But staph didn't go away; it mutated and multiplied. By the mid-'80s, scientists were scrambling to create new antibiotics to do what the older ones, including methicillin, no longer could.

In some people, anyway. If staph, despite its prevalence and potential viciousness, hasn't sounded the same alarms as other epidemics, maybe it's because while it maims, blinds or kills some, it causes just a minor rash in others. Or maybe it's because, for a while, that scariest version -- methicillin-resistant Staphylococcus aureus, or MRSA -- was found only in hospitals, preying on the already incapacitated.

Now, though, staph is bringing down the strongest and healthiest among u -- —athletes -- many of whom were nowhere near a hospital when they became infected. High-profile names in every sport have been put on the shelf: former MLB slugger Sammy Sosa, White Sox outfielder Álex Riós, Grizzlies forward Rudy Gay, Rockets forward Shane Battier, Nuggets forward Kenyon Martin. Ex-middleweight champ Kelly Pavlik nearly died from an infected cut on a knuckle. Staph has killed high school and college football players -- including Ricky Lannetti, a record-setting Division III wideout -- and ended the careers of pros such as Redskins defensive lineman Brandon Noble and Browns wide receiver Joe Jurevicius and All-Pro center LeCharles Bentley. Today, it pops up wherever people congregate in less-than-sanitary environments: prisons, day-care centers, high schools. And yes, athletic facilities.

"If you don't know what MRSA is, you should," says Helen Boucher, an assistant professor at Tufts University medical school and a resident physician specializing in infectious diseases at Tufts Medical Center. "It can strike -- even kill -- otherwise healthy people. It can be prevented, and treated, but only if it's caught in time."

Which can be tricky. Staph needs only a few days to do its irreversible damage. Meanwhile, it can take 48 hours to determine the strain of the bacteria that's causing the trouble. Staph doesn't always blow up a joint or finger to announce itself, either, instead doing its dirty work more subtly, eating into tendons, nerves and bones. Then the only solution is to flush out the infection, pump in a cocktail of antibiotics and pray. According to reports citing anonymous sources, that's what Patriots quarterback Tom Brady went through two years ago after contracting a post-knee surgery infection.

One report, which appeared in The Boston Globe, didn't shock Boucher. "We see it every day," she says, "at nearly every hospital in the country."

DON'T WHINE ABOUT bumps and bruises. Play through pain. That's the sermon of sports. But these days, being a warrior can mean never going to battle again. Noble, the former Redskin, is proof. At home after undergoing arthroscopic surgery on his right knee 5½ years ago, he watched a quarter-size wound on his knee grow over the entire area, then discolor his whole leg before he took the advice of his mother-in-law, a nurse, and returned to the hospital. Doctors told him that if he'd waited another 24 hours, he could have been dead. After two days of treatment, pus that Noble describes as "green mayonnaise" began to ooze from the incision.

Recovery took months. Eventually, he did get back to the practice field -- where he promptly tweaked the other knee. Surgery followed, and with it another infection, the joint swelling to the size of a football. "The hospital points at the team, and the team points at the hospital," Noble says. "Nobody knows how I got it."

At least Chris Kaman knows where he got it. The Clippers center was vacationing on Kauai two summers ago when a mosquito bit his calf. By the time he boarded a fishing boat on the Big Island a few days later, the bite had turned into a pus-rimmed volcano and pain radiated through his leg. "I didn't know what it was, but I was scared," he says. Fortunately, a nurse in his party sent him immediately to a hospital. After a week of antibiotics, Kaman went home, but with a permanent divot from the infection in his calf. Had he been on one of his more remote trips -- fishing off Mexico, say, or RV-ing in Alaska -- or been in less-astute company, he might have joined Noble in retirement. Or worse. Instead, he was back for opening night in 2009 and became a first-time All-Star.

"I think people just don't understand," says Suns forward Grant Hill. "It will take the death of someone young and high-profile for us to take it as seriously as we should. We haven't had our Rock Hudson yet."

Hill was nearly that someone. After two injury-plagued seasons with the Magic, he underwent reconstructive ankle surgery in the spring of 2003 at Duke University Hospital. Recouping in Orlando, he felt achy and worn out. On Day 4, he went into shock and began to convulse. He thrashed in his seat, eyes wide with panic, as his wife, Tamia, sped him to the emergency room.

Doctors suspected staph-induced blood clots in his chest and placed him in a hyperbaric chamber. But when Hill unwrapped the bandages around his ankle, he found a gaping hole at the site of the incision. He sent a cell-phone photo of the wound to his doctors in Durham, and they had him fly back right away. For the next six weeks they pumped him with heavy doses of vancomycin and grafted skin from his arm over the gap. At the end of the ordeal, Hill was ready to retire rather than risk future hospital visits. "I thought if I got hurt again and had to get another surgery, I could die," he says.

Alas, not everyone in sports has been scared straight. Timothy Trainor, a consulting physician for the Nevada State Athletic Commission, says because we all have staph on our bodies and because current antibiotics are plenty effective, he will disqualify a fighter only if he has pus or fluid oozing from a wound.

Experts counter that an infected fighter, even if he isn't sick himself, leaves an invisible trail of staph everywhere he goes. That staph lies in wait for someone, particularly someone who isn't a pro athlete and therefore isn't as body conscious or doesn't have a paid staff keeping a close eye on anything that might impact his livelihood. And often that someone won't have the resources or knowledge to deal with the infection when it strikes. Someone like DaVonte King.

DaVonte and his mom, Brenda, live in Green Bay, Wis., where a love of football is a birthright. He was 13 the day he came home from football practice complaining about his head and ankle. He had no visible cuts or bruises, certainly no oozing, so Brenda took him for X-rays. The diagnosis was a sprain, and he was sent home, cleared to go to school the next day. But the Kings had to rush back to the hospital the third night, after DaVonte started to spit up blood. This time nurses ran a full battery of tests and discovered a septic blood clot. He was airlifted to a Milwaukee children's hospital, where he spent the next 50 days, a month of that on life support. His left leg was amputated just below the knee.

King lost his leg below the knee after contracting MRSA three years ago, but not his spot on the varsity squad. Mike Roemer

After finding out MRSA was diagnosed in a teammate as well, Brenda now suspects DaVonte took a contaminated cleat to the ankle. She still struggles with the fact that she had no idea MRSA existed, much less that it could put her at a bedside for weeks, listening to a ventilator fill her son's lungs as IVs slowly dripped into his arms. "Everyone knew about swine flu, bird flu -- they were on TV constantly," Brenda says. "But this gets shoved in the corner. Even at the hospital, it's hush-hush. How can that be?" She says that Green Bay hospital now screens patients for MRSA upon arrival. DaVonte, now 16, mans the line for Northeastern Wisconsin Lutheran High on a prosthetic leg.

Nick Mullins, a former pro skateboarder, also went to the hospital after feeling "crappy" a day after landing on his hip at a skating spot near his home in northwestern Ohio. A doctor cleaned the scrape and said he'd be fine. When Mullins felt worse the next day, he went to a different hospital; this time he was told he had folliculitis, an infection of the hair follicles, and was given an oral antibiotic. He doesn't remember walking into the third hospital a few days later; he only knows that when he awoke he couldn't move his arms or legs. After he lost consciousness, he'd been placed in an induced coma and airlifted to a Michigan facility, where he was given a 1 percent chance of survival. Mullins was in intensive care for six weeks, the infection coursing through his body, eating into the retinas of both eyes. After multiple surgeries, he has regained 15 percent of his vision in the left eye; a curtain of hair obscures the useless right one. "I'm happy to be alive," he says. "But I wouldn't be in the condition I'm in if they'd figured it out right away."

Or if he knew enough to suggest it, which he might have if pro teams and star athletes weren't so reluctant to talk about their own brushes with staph. Ki-Jana Carter, a former NFL running back, is a self-described "germ freak" who endured eye rolls when he brought his own towels to work after being drafted No. 1 by the Bengals in 1995. With the Saints midway through the 2003 season, he discovered a bump on his left biceps that spewed the telltale green mayo. According to Carter, it was one of 10 MRSA cases the team had that season, but no outbreak was ever reported. (The team declined to comment.) Carter, who was never the same after tearing a knee ligament three plays into his first preseason game, certainly didn't say anything. He knew fringe players couldn't afford to rock the boat. "From the team's perspective, they want to ease everybody's worries," says Carter. "And the player is worried about public perception. People might think he's unsanitary. But as a teammate, I want to know if someone has something contagious, because I could bring it home to my family."

Among the major sports leagues, the NFL has had the most reported cases of MRSA: 33 were reported league-wide from 2006 to 2008, according to a team physicians' survey. But as Carter's experience suggests, it's a good bet not every case was reported. Brady nearly missed the 2009 season because of his infection, yet to this day neither he nor the Patriots has acknowledged he had MRSA, much less talked about what he's doing now to avoid another bout. The Browns have had at least five MRSA infections, but when one of the infected, Kellen Winslow Jr., accused the team of covering up the threat, the tight end was reprimanded and was going to be suspended, until he appealed. He was soon traded. Colts quarterback Peyton Manning had a knee infection that required the removal of a bursa sac. The Colts have said only that it wasn't MRSA. "That's something I don't think Peyton wants to discuss," says a Colts spokesman.

Hill is an anti-MRSA advocate now, but at the time of his illness he didn't explain why a projected five-month recovery stretched to 16. People just assumed his ankle wasn't sound, and he was content to let them. Admitting his body had betrayed him, while not knowing how or why, was simply too difficult. "I didn't talk to my friends about it, much less the media," says Hill. "I was too scarred by the experience."

Personal privacy issues, malpractice lawsuits and the desire to prevent panic have kept staph on the down low. They also keep younger athletes at risk. Outbreaks are still being reported at high schools across the country, a testament both to the continued lack of awareness and staph's perniciousness. The varsity football team at Sherwood High in Maryland's Montgomery County was hit three years ago. Seven players were infected; some were hospitalized. The cases were part of an epidemic that hit 31, causing one death, in the greater DC area. Sherwood's nurse, Jennifer Jones, has since done all she can, from addressing the football team while holding a bat to producing a student-crafted rap video about staph, to raise awareness and diminish the stigma. "It's an icky thing—maybe that's why they don't deal with it," Jones says, of professional athletes' reticence to talk about staph. "But it sure would help if they'd talk. If pro athletes campaign against diabetes or anything else, it draws attention. You have to hammer into students and parents just how serious this is."

STAPH'S LOW PROFILE has another negative effect: tamping down funding for the development of new treatments. So prevention is crucial. And the steps are simple. Wash hands and equipment regularly; don't share towels or razors; cover wounds with an antiseptic bandage. The hand sanitizers, alcohol wipes and stacks of freshly laundered towels at your local health club probably don't come with flyers about staph or MRSA, but they should.

A more sophisticated preventive industry has also emerged. Two years ago, Carter started ByoGlobe, one of several companies that specialize in making buildings and their interior surfaces bacteria-resistant. ByoGlobe, which uses a negative-electrostatic-charged sprayer and a special eco-friendly solution to coat suspect areas, counts the Bengals, Dolphins and Penn State football among its clients. But ByoGlobe isn't alone: Coating Specialists, a company that also dispenses antimicrobial applications, has done business with the Yankees, Redskins, Magic, Notre Dame and the U.S. Army. Another firm, AtmosAir Solutions, provides technology that attacks airborne bacteria; its clientele spans most major sports, from Thrashers to Chiefs to Mariners, and is currently negotiating with an NBA team. Considering games and practices lost, and that employing any of these companies would cost a team far less than the minimum salary of a single player, it is baffling that so few teams use one. "Teams will pay anything," Carter clarifies. "But only after something happens."

When other NBA teams heard about the Celtics' outbreak, some instituted new policies. The Spurs, for one, tell arena workers to keep fans from touching players as they run out to the court, and players are reminded to wash their hands thoroughly after autograph sessions and community appearances. But no team is as meticulous as the C's. Everyone in Boston's basketball operations -- from GM to administrative assistant -- is swabbed. Those who test positive receive a staph-killing cream in their nostrils each day for a week. Everyone is instructed to sanitize and cover all wounds and to shower before climbing in a hot or cold tub. Players soak alone and drain the tub afterward. And they are asked to please, please, report any cut, scrape or bite that appears to be getting worse. Posters outlining the grisly effects of MRSA hang in the training room. A player in need of further motivation need look no further than the locker room.

The problems started in training camp when an infected ingrown toenail caused West's foot to swell. Pierce then showed up for a shootaround in New Jersey with the middle finger of his left hand so swollen he couldn't catch the ball. "A doctor cut open my fingernail, flushed out everything and put me on antibiotics," Pierce says.

In February, he was sent home again, this time from Detroit, with a fever and swollen left elbow. It too was lanced and drained, and Pierce spent two days in the hospital. Lacerte says the Celtics had four cases that season. After losing games because of it, they decided to root out the cause.

Team officials had 50 different surfaces at their facility tested for MRSA, then hired a cleaning company to sanitize everything. New pre- and postpractice procedures for keeping it all clean were put in place. Today, the franchise routinely retests and resanitizes surfaces. Boucher says staph can return to the same spot in 60 days. "It may be overkill," Lacerte says. "But we haven't had a problem since."

When Pierce slides off the training table these days, Lacerte wipes it down with a microbial disinfectant before Shaq heaves himself onto the same shamrock-green pad. After Shaq leaves, Kevin Garnett is given the same courtesy. But Lacerte knows he can do only so much.

The most troubling part of the outbreak four years ago is that the Celtics eventually determined the bacteria didn't originate in the facility. Besides, no matter what they do at home, the team still is going to be heading elsewhere at least 41 times -- to other training rooms, other courts, other weight rooms. MRSA is almost certain to be at most of them, posing way more of a threat than an aging center ever could.