Let me add my 2 cents on this topic as I have just come back from my first Camino (Frances) last week so the experience is very recent. I will try to focus on facts, share my observations and some suggestions for what they are worth - Perhaps it will be useful for other pilgrims on the Way.
1. Bed bugs in the Camino are no myth. Anyone claiming so look to me as playing a sad joke. I was bitten by them on three occassions during the last month starting with Burgos, then Carrion and finally somewhere close to Santiago. That also proves to me that the bed bugs were active (not in "winter-hybernation" mode) already for a while despite that the weather was not very warm yet (in fact, I am sceptical about the idea of winter making the BB much less active as most albergues that are used by pilgrims during winter keep it warm enough inside).
2. I have limited, but noticable body reaction to BB bites and I am a light sleeper so I would wake up when I feel being bitten even if I can confirm that the bite does not feel more than a mosquito bite (at least to me). In all of the cases I managed to catch and kill at least some of the BBs biting me. So I am sure that was BBs and their bite marks on my body.
3. The people who claim they never encountered the BB on the Camino are either of a) exceptionally lucky or b) have not noticed the bites nor the bugs. I have met people in the same albergues who did not think they ever been bitten, but after my advice to inspect their bodies carefully some found bite marks. For some people, the reactions are literally easy to miss.
4. That may lead to a (wrong, in my mind) idea that one may not care about the BB and their bites in virtual absense of one's body reaction, but there are two important points - the responsibility to not spread the BB along the Camino and the wish not to bring them home. Following the earlier advice of
@Kanga and others (on another thread on BB) I did all I could after each encounter to minimize the possibility of both risks. I tumble dried at high heat all I could (including the backpack) and applied DEET to the rest. I even used the "sauna method" - walking into sauna with all my things that could not be tumble tried when sauna was available. I also informed the hospitaleros of the BB encounter so that they can take their measures.
5. I have no knowledge of what the hospitaleros did to counteract the spread of the BB at the albergues where I got bitten, but at least they were informed and had their chances. In some other places - and it happened to be some three places run by hospitaleiros from anglo-saxon lands, perhaps not a coinsidence - I witnessed some proof that they take the fight againgst BB spread seriously. In one place (Granon) they used hot steam regularly on the mattresses and the sleeping space, plastic bags for each backpack (Pieros) or claimed they offer extensive treatment procedure for those bitten and potentially carrying BB (Rabanal). I do not know if the albergues use chemicals (like permethryn or DEET), but I would suspect that some do (I noticed the spray bottles present at some).
6. Then there is a question that continues to spin in my mind - if my efforts to get rid of BB after each encounter were successful and I was each time attacked by a new sample of BB living in that albergue or not. I did not have any "protection" until I was bitten the first time. By the end of the journey I had permethryn-impregnated bedsheet, a spray bottle of 45% DEET and another spray containing permethryn plus other ingredients. What bothered me was that the last time I was bitten I was using the bedsheet and some DEET on my open body (that looked a nice and clean albergue and I did not spot the BB traces so I felt reluctant to use much protection there). Still I was bitten by 1 bug that I suspect has travelled to my pillow by the wall. And that raises a question if the BB are perhaps getting resistant to the chemicals as that bed bug(s) seemed not to care much.
7. Some advice on where to get the chemicals in Spain in case you decide to use them. I was surprised to have difficulty to find permethryn-based spray in the pharmacies in Spain, on the Camino given that BB must be not uncommon problem. I have gone to litteraly more than 10 pharmacies before finding such spray just during the last days of the journey, the name "Farma Zum Cinches y Pulgas". Before the best I was offered was a DEET based spray from GOIBI brand. It was supposed to be a suitable alternative to permethryn (although some doubts remain for me regarding its efficiency). The benefit of DEET is that you can spray it on the skin which is not recommended with permethryn, but DEET can damage some of the synthetic materials while permethryn doen't. I bought the anti-BB bedsheet at an outdoor shop in Leon.
8. So what is the ultimate solution? Be lucky. If you can't or are not so confident about your luck - try to prepare beforehand. The next time I would treat my backpack, sleeping bag, silk liner with permethryn before the trip (letting it dry in a ventilated space) and bring the anti-BB bedsheet with me. That does not guaranty anything, but I understand that it reduces the chances to meet BB on the Camino. I would continue to use the thorough inspection of the bed before settling, although I only spotted something suspicious once. And I try to take good care of my things after I come home - all go through either heat (dryer, sauna, oven) or cold (freezer) treatment. I hold my fingers crossed that is enough and I won't have brought the BB home.