"by the early 20th century (1907) Americans had a very good
understanding of how infectious TB was"
TB has got to be one of the most deadly and prevalent diseases ever.
Some people call it the 5,000 year old epidemic. TB still kills tens
of thousands of people each year. People knew way, way before the
20th century how very infectious it was. The first modern
description was published in the 1540's, but it was also described by
Hippocrates. That pesky little Mycobacterium genus is fairly young
(about 15000 years) and researchers think that its evolution
parallels our switch from hunters to farmers. Mummies dating to
3400BCE have been found with it. In the 1700's, just about everyone
in Europe was probably infected. In general, there are three stages:
first is the infection and tubercle formation, but there are very few
symptoms and it is often dismissed as a mild cold (just like in the
NHK drama). The second stage is a dormant stage, that can last from
weeks to a life time. As long as the host remains healthy they may
never show any symptoms. The third stage is the one we are familiar
with, the tubercles open and the bacteria spread throughout the
body. In the pulmonary form, sputum and sometimes blood are coughed
up. This is also a means of transmission. Prior to the 1940's
(development of vaccines and anitbiotics; mostly done in Europe) the
most effective 'treatment' was to forestall the 3rd stage and to
prevent the spread. Sanitoriums provided people with quiet,
nutritious food (very similar to the orders of that wonderfully
cranky doctor in the NHK drama), clean conditions, and were a type of
quarantine.
Probably a good number of the folks in the Shinsengumi (and in Kyoto
and Edo and any other large city) had an infection, but only poor
Soji is described as having the final stage of the pulmonary form.
Who knows when and where he got it? But I can certainly imagine the
living quarters at Mibu and stress levels leading up the raid on
Ikeda as being factors causing him to move to that third stage.
Given how common it was/is I am a little surprised that more men are
not listed as having it. But there are several other ailments that
are actually TB that are often misdiagnosed, so maybe others did have
it. And it is much more tragic in some one so young, which makes a
much better story, eh?
These sites have other interesting historical tidbits
http://www.lung.ca/tb/main.html
http://www.jantb.com/historytb2.html