During the Black Plague in the 14th Century, physicians wore a predecessor of the modern Hazmat_Suit: A waxed, ankle-length leather coat, a mask resembling the head of a bird, and a short, wide-brimmed hat (or a hood). The beak of the mask was filled with posies, which was believed to filter out "Miasma" (the literal stink of disease, which was erroneously thought to be the vector of infection). The overall effect was extremely disconcerting, leaving the costume forever associated with epidemics.
The costume itself was surprisingly effective: Inflected fleas couldn't cling to the waxed leather, and posies contain a chemical that destroys bacteria. However, the bacteria itself would often cling to the outfit, causing the doctors to accidentally spread the infection.