10. Jeanie Boulet Tests Positive For HIV
Jeanie Boulet, played by Gloria Reuben, was introduced toward the end of ER's first season as a carer for Peter Benton's mother, before the two embarked on an affair. However, Jeanie was married to Al Boulet - a man who had been cheating on her repeatedly, leading to his diagnosis with AIDS.
In the third season opener, Jeanie reveals to Peter that she has tested positive for HIV. This was a crippling blow to their relationship (Peter ends things quickly after this) and was the beginning of a long and hard road for her. Her status as a physician was uncertain, as the diagnosis threw her ability to perform any procedures on patients was in doubt.
She would particularly clash with Dr. Weaver over this - she felt she was perfectly capable of continuing to practice medicine, while Weaver was ever-conscious of the lawsuits that could come from even the slightest accident.
Jeanie had to deal with many rough blows throughout her tenure in ER - but this was truly the worst of them.