at a walkerton, ontario hospital in may 2000, numerous individuals of all ages were coming in with fever and bloody diarrhea. the epidemiologists at the local health department suspected an outbreak of e. coli o157:h7. after weeks of searching, they traced the outbreak to the town's water supply. when questioned, the town's water manager admitted to lying about properly treating the water and was later arrested for negligence. the e. coli o157:h7 strain isolated from victims was matched to a strain found in a herd of cattle on a farm near one of the water wells. seven people died during the epidemic. which approach to dealing with the epidemic would not be useful for preventing further illnesses?