Others aren't so fortunate. In many cases, PID goes undetected for so long that it robs women of their fertility and reproductive health. Understanding PID PID is an upper genital tract infection that's diagnosed in an estimated one million American women every year. The infection moves into the upper genital tract and PID develops. There are several theories on how organisms move up from the vagina into the uterus.
Some experts say it is possible that organisms initially attach to the cervix.
A mucus plug that seals off the uterus during the other phases of the cycle is expelled at menstruation, and the cervix is open for organisms to pass through. Others believe that the organisms attach to sperm and essentially hitch a ride up. The uterus is normally a sterile environment, so when bacteria or sexually transmitted organisms that don't belong there enter, trouble may develop. The organisms can penetrate the endometrium, or lining of the uterus, causing an inflammatory condition known as endometritis, which may be painful. They can also attack the fallopian tube, infecting and damaging its lining.