What did these doctors conclude about the main cause of the outbreak of the Black Death?

Bacteria

Explanation:

Not sure which time periods doctors you are referring to, but modern day scientists have concluded that the bubonic plague, or black death was caused by a bacteria called Yersinia pestis. This bacteria originated in asia and was spread to europe via ship and trade routes. The bacteria was carried by the lice and fleas on rats, which carried the plague onto ships and around the world.

bad air