Conversation so far:
What was the Great Plague?
The Great Plague, lasting from 1665 to 1666, was the last major epidemic of the bubonic plague to occur in England.
What happened to the poor during the Great Plague of London?
The poorer people were alarmed by the contagion and some left the city.
Did the poor become sick during the Great Plague of London?
Records state that plague deaths in London and the suburbs crept up to over 7,000 per week in September. Many of the poor were just dumped into mass graves unrecorded.
Around what year was the Great Plague of London happening?
The Great Plague, lasting from 1665 to 1666, was the last major epidemic of the bubonic plague to occur in England.

Question: What was the cause?
Self-contained rewrite: What was the cause of the Great Plague of London?