Yeah, I know, sounds like some ridiculous clickbait, but hopefully worth a read.
Sometimes, with TB, it's in a condition called latent TB for some time, where it's manifested itself within the lungs but doesn't make the person ill - it's basically dormant. It only becomes active if some kind of physical or emotional trauma happens, in which the immune system weakens and the bacteria take hold. Given that Arthur was infected in Chapter 2 but didn't show signs of illness until later, it may have been the case with him. But if so, when did he begin showing signs of illness and what might have caused it?
Although Guarma is the time most players might say Arthur starts to seems unwell (deer/coyote vision, struggling to keep up with Dutch and the others while running away from the soldiers in the first mission there, some coughing, etc), I'd say it was before that. The deer/coyote visions happen when Arthur is dying, yet the first one happens in chapter 3 - immediately after the O'Driscoll mission. I think that's telling, as it suggests that something about Arthur is changed. The fact that they only get more common as Arthur's illness progresses is even more interesting.
What's more, it was certainly a traumatic event. Arthur was shot in the shoulder, tortured, hung upside down and ultimately bedridden for a few weeks. That's a serious injury - Swanson even notes that he thought he'd be burying Arthur. Something as severe as that is the kind of trauma that would present a perfect opportunity for the infection to become active and no longer be in latent form.
Going back to when Arthur is first ill, it would be chapter 4. Sure, no sign in the "wellbeing" section, but the subtle signs are there. Arthur coughs a bit just before entering Bronte's mansion at the beginning of the chapter, again after Strauss tells him to go after Algie Davsion, and I think a few other times too. In fact, Arthur actually writes in his journal: "Keep feeling sick but I'm sure it's nothing. Whole place gives me the creeps" towards the end of the chapter. It does seem as though he was slightly ill already, which, when combined with a deer/coyote vision and a traumatic event that's relevant for the context of how TB can progress, I think it makes a fairly strong case that it was the revent O'Driscoll mission that activated his TB and thus played a part in his death.
We can't blame it totally on this, though, as Guarma was another traumatic event that seemed make him worse still and perhaps would've triggered it anyway if the O'Driscoll mission never happened. The stress of losing Hosea and Lenny, escaping, being thrown overboard, half-starving, dehydrated and badly sunburnt (perhaps even to the point of sunstroke) was clearly bad for Arthur, but as it happened, I think that only ended up being a facilitating factor instead of the root cause (which I think it would've been had it not been for the O'Driscolls) of Arthur's illness becoming active. By the end of chapter 3, it seems that Arthur was already doomed.
