To prepare for the big game this Sunday, some of America’s top athletes will run drills and watch film to anticipate the other team’s strategy—but even the best players cannot predict what might be their fiercest opposition. As former NFL defensive tackle Brandon Noble said , "The worst and most unexpected thing that I have come up against in my football career has been a tiny little thing that I cannot see." In 2005, he was one of about 368,000 Americans to be hospitalized with an antibiotic-resistant infection known as MRSA. Athletes are among those at particular risk of contracting MRSA,...