I think a lot of people are also under the impression that cotton fever is actually getting a small fiber of cotton into your bloodstream after drawing it up and not having to do with sanitizing the area. I dont know if you guys do think that, but many actually do
It is confusing and after (quite extensive) searching all I can find are papers stating completely opposing views, haha.. The general opinion seems to be that it is a bug (Enterobacter agglomerans) which grows on the cotton plant entering the blood stream, causing you to become sick while your immune system deals with it, then subsiding as the bugs are destroyed. Cotton feaver doesn't usually develop into full-blown septicaemia - although it can, so if the symptoms are not easing or you are getting more unwell please get help straight away - especially if you have persistant high temperatures, feel dizzy/dehydrated/woozy, aren't peeing and have persistant rigors/shakes.
Essentially, the symptoms fit with a shower of bacteria entering the blood stream, the body rallying it's immune system and taking care of it before it develops into sepsis - but making you feel pretty shitty while it does so. It could be caused by a wide range of bacteria, so not all cases of "cotton fever" could have the same root cause, and it could also theoretically be an immune response to foreign substances (cotton fibres) in the blood stream but I haven't read much evidence to support this theory.
To avoid it - be as sterile as possible, clean your hands well, never reuse cottons (the will be full of bacteria), in fact don't use cottons at all - use a
micron filter - and sterile (ideally bacteriostatic) water plus a fresh needle each time. Swab the skin properly with alcohol swabs (30 seconds then let dry) first. This still doesn't guarantee you won't introduce bacteria into your blood stream, but it will minimise the risk as much as possible.
There is no pharmacological reason (as far as I can think) that would mean cotton fever blocks opioids except that you are unwell (temporarily) and you may well not feel the opioid as much, plus you are probably redosing sooner than you usually would to try to make yourself feel better - so the effects of the dose feel reduced.