LONDON - When James Wollacott badly wrenched his knee while jumping on a trampoline in the back garden of his house, the healthy, athletic 20-year-old imagined a quick operation and a swift recuperation. Instead, he spent three months in the hospital last year, bedridden and gravely ill, battling high fevers and a merciless staph infection. The infection was M.R.S.A., short for methicillin-resistant staphylococcus aureus, known as the "superbug,'' and Mr. Wollacott picked it up when doctors inserted in his kneecap four titanium pins. More than a year after his accident, Mr. Wollacott, who lives in Essex, still has trouble walking,...