HIV and other immunocompromised patients are at risk for developing drug-resistance strains of herpes simplex virus. It would seem logical this could apply to EBV, CMV, and HHV6 as well. The immune system problems seen in CFS, possibly due to XMRV, mean that we also could develop resistant strains at a rate that parallels the rate seen in HIV, which is about 5 to 7 percent of patients--which isn't too bad but is still 10 times the rate seen in people with normal immune systems. Drug-resistant herpes simplex virus in HIV infected patients. "However, with the emergence of drug-resistant strains of HSV2, the rates of resistance among HIV patients are almost ten-fold those in immunocompetent individuals, comparing 0.6% to 6%" Herpes simplex virus resistant to acyclovir. A study in a tertiary care center. "Herpes simplex virus resistant to acyclovir arises relatively frequently in immunocompromised patients" Survey of acyclovir-resistant herpes simplex virus in the Netherlands: prevalence and characterization. "resistance is low in immunocompetent patients (0.27%), whereas ACV-resistant HSV infections occur relatively frequently in immunocompromised patients (7%; P < 0.0001)" Valacyclovir for herpes simplex virus infection: long-term safety and sustained efficacy after 20 years' experience with acyclovir. "Extensive sensitivity monitoring of HSV isolates confirmed a very low rate of acyclovir resistance among immunocompetent subjects (<0.5%). The incidence of resistance among immunocompromised patients remains low at about 5%."