The great fire had done a good work by sweeping off many causes and centres of infection, and there had come wider streets, better pavements, and improved water supply; so that, with the disappearance of the plague, other diseases, especially dysenteries, which had formerly raged in the city, became much less frequent.
But, while these epidemics were thus checked in London, others developed by sanitary ignorance raged fearfully both there and elsewhere, and of these perhaps the most fearful was the jail fever.

The prisons of that period were vile beyond belief.

Men were confined in dungeons rarely if ever disinfected after the death of previous occupants, and on corridors connecting directly with the foulest sewers: there was no proper disinfection, ventilation, or drainage; hence in most of the large prisons for criminals or debtors the jail fever was supreme, and from these centres it frequently spread through the adjacent towns.

This was especially the case during the sixteenth and seventeenth centuries.

In the Black Assize at Oxford, in 1577, the chief baron, the sheriff, and about three hundred men died within forty hours.