The earliest medical work printed in English is Treatise on the Pestilence published without printer's name or date, but attributed to the press of William Machlinia, in London, and estimated to have been published in 1483. It survived in only a single copy preserved at the John Rylands Library, Manchester.
"Although often attributed in incunable editions to Benedictus Kamisius, Kamintus, Canutus or Kanuti (i.e. Bengt Knutsson, bishop of Västerâs), the author is probably Johannes Jacobi (i.e. Jean Jasme or Jacme) (Wickersheimer)" (ISTC no. ij00013200).
J. F. Payne, "The Earliest Medical Work Printed in English", British Medical Journal v.1 ; May 11, 1889, 1085-86.