Federal regulators are dropping plans to tightly control a procedure that is becoming increasingly popular for treating people stricken by life-threatening infections of the digestive system. The Food and Drug Administration says the agency will exercise enforcement discretion and no longer require doctors to get the agency's approval before using "fecal microbiota for transplantation." The procedure is being used to treat people suffering from infection with the bacterium Clostridium difficile, or C. diff. These infections cause inflammation of the colon and severe, sometimes life-threatening diarrhea. They can be extremely difficult to treat and are becoming more common. About 14,000 Americans die from C. diff every year, according to the federal Centers for Disease Control and Prevention.