What was the most common form of plague?

The most common form of plague was the bubonic plague, which was caused by the bacterium Yersinia pestis. This form of the plague was characterized by swollen lymph nodes, or buboes, which would often appear in the groin, armpits, or neck. Other symptoms included fever, chills, and vomiting. The bubonic plague was often fatal, with a mortality rate of around 50%.