About one million women develop it each year, but perhaps as many more may not even know they have it. With the exception of AIDS, pelvic inflammatory disease (PID) is now considered the biggest sexually transmitted threat to women’s health. An infection of the uterus or fallopian tubes, PID can lead to infertility, ectopic pregnancy (in which the embryo lodges outside the uterus, commonly in the fallopian tubes), or internal problems that may require surgery to repair. Severe cases can be fatal:...