The author encourages us to see illness not as an ontological object, but as an epistemological phenomenon. That is, the line of demarcation between what is considered illness and what is not is arbitrarily drawn by medical professionals. Iwata lays out his idea, giving a detailed account of how some illnesses became what they are now. Although the key idea does not sound so radical for a student of humanity, the procedure in medicine and typical misunderstanding introduced in this book were a good read.
As a specialist of infectious disease, the author is known for criticizing the government's policy against COVID-19 spread. I am not ready to judge the validity of his argument that the ontological handling of the virus caused the seeming failure. However, I think he's right in arguing that the patients are more comfortably treated when doctors and the patients themselves emphasize their values in life, and stop sticking to the presence of pathogen, lesion, or the complete healing of it.