Worse, smallpox raged.

From 1776 by David McCulough. Page 60.

The first snow fell on November 21, and in the days to follow it was obvious winter had come to stay, with winds as bitter as January and still more snow. The distress within Boston was reportedly extreme. The British were cutting trees and tearing down old houses for firewood. Supplying the besieged city by sea had become increasingly difficult because of winter storms and American privateers. Food was in desperately short supply. The King’s troops were said to be so hungry that many were ready to desert at first chance. Some of the redcoats said openly that if there were another action and they could “get off under the smoke,” they would choose “the fresh beef side of the question.” Men in their ranks were dying of scurvy. Worse, smallpox raged.

Meanwhile, deserters from the American side were telling the British that Washington’s army was tired and unpaid, that there was too little clothing to keep warm, and that most of the men longed to go home.