Sentence:  An artificial kidney these days still means a refrigerator-sized dialysis machine. Such devices mimic...real kidneys.... But they are nothing like as efficient, and can cause bleeding, clotting and <WSD>infection</WSD>—not to mention inconvenience for patients, who typically need to be hooked up to one three times a week for hours at a time. 
Meaning of the word marked with <WSD> tags:  An uncontrolled growth of harmful microorganisms in a host.