There isn't much in this world to truly fear

Buuuuut I think this one qualifies. Hemorrhagic streptococcal pneumonia was observed in three patients who came in complaining of a cough. 12 hours and several rounds of strong antibiotics later, the patients were dead. Autopsies showed lungs that should outwardly appear pinkish that were dark red with hemorrhage. Here's the scary part: the streptococci were susceptible to the antibiotics that were used. 

Sleep tight, kiddies. 

http://wwwnc.cdc.gov/eid/article/20/1/13-0233_article.htm