Some parasitic infections can be passed from person to person. The most common way this occurs is when food that has been prepared by someone with an infection is eaten. In some cases, the condition can be spread by a tainted blood transfusion or when sharing a needle with someone infected. Parasites like Cryptosporidium can be spread through drinking or recreational water. Worldwide, it is most common to get a parasitic infection through contact with an insect (such as malaria) than through contact with another human being.