They live in New Mexico, which has pretty good air quality in terms of outdoor biotoxins.
I never wholly believe that a house is good until I visit it myself, but Dr. Deckoff-Jones assures me that her house (where her family has lived for a number of years.....not the one where everybody got sick) is good in terms of not having a toxic mold problem.
Lo et al talk about the possibility that the presence of XMRV could "reflect an increased susceptibility to viral infections due to an underlying CFS-related immune dysfunction, rather than a primary role for these viruses in the pathogenesis of CFS."
And the Courgnaud et al commentary (also in PNAS) mentions the possibility that more than one "environmental agent" may have an impact on whether the retrovirus becomes pathogenic:
"These observations suggest a scenario in which retroviruses, MLV- related agents [MLV = murine leukemia virus] and potentially, other viral agents may cross-complement to promote coinfection and enable pathogenicity. The current data suggest that a variety of xenotropic and polytropic MLV can be found in North Americans with and without disease. To add to this bewilderment it is likely that more than one environmental agent impacts on the development of both CFS and prostate cancer."
I thus suggest that one possibility that some people might do better than others on these drugs is because of differences in terms of their living environments.
I've discussed in other places on this board why toxic mold has the potential to be a particularly important environmental agent, compared to other alternatives.