How can ovarian cysts become infected?

Unlikely: Ovarian cysts are unlikely to become infected unless you have an infection in the uterus and tubes. They form in the sterile environment of the ovary and are usually not exposed to germs. If you do get a bad infection in the uterus or fallopian tubes, the infection can spread to the ovary and create a tubo-ovarian abcess. On ultrsound this looks like a large ovarian cyst that is infected.