Prevalence of HTLV types I and II among drug users in King County, Washington.

We investigated the prevalence of human T-cell lymphotropic virus (HTLV) types I and II among drug users entering treatment in King County, Washington, between 1988 and 1990. Of 762 injection-drug users, 81 (10.6%) were HTLV-positive; of 89 noninjection-drug users, 2 (2%) were HTLV-positive. Most (95.8%) of those typed) were HTLV-II-positive. The relationship between HTLV and demographic and behavioral characteristics was further evaluated among injection-drug users. The prevalence rates for HTLV increased 25-fold from the youngest age group (15 to 24 years) to the oldest (older than 45 years), after adjusting for race. After adjustment for age, American Indians or Alaska Natives were 7.9 times, blacks 6.2 times, Asians or Pacific Islanders 4.7 times, and Hispanics 4.1 times as likely as whites to be HTLV-positive. The prevalence of HTLV among heroin injectors was more than double that observed among injectors of other drugs after adjusting for age, although this association was only marginally significant. The strong association between HTLV prevalence and age suggests that HTLV-II (the predominant virus) has been endemic among King County injection-drug users for some time. Its relatively high prevalence indicates that there is both an opportunity and a need to further investigate the epidemiologic and clinical implications of HTLV-II infection.