CLUSTERING OF HUMAN T-LYMPHOTROPIC VIRUS TYPE-I SEROPOSITIVITY IN MONTSERRAT, WEST-INDIES - EVIDENCE FOR AN ENVIRONMENTAL-FACTOR IN TRANSMISSION OF THE VIRUS

A community survey of human T cell lymphotropic virus type I(HTLV-I) i n Montserrat, West Indies, identified 22 instances in which 2 HTLV-I-s eropositive adults lived within 60 m of each other (close pairs), comp ared with 7.8 expected (P < .001). Five of these close pairs were moth er-offspring or husband-wife. The remaining 17 pairs were of unrelated members in separate households. The percentages of male-female (41%), female-female (41%), and male-male (18%) types in these 17 pairs were very similar to those among the 1377 similarly defined pairs in which neither or only 1 member was seropositive, affording no support for e xtramarital heterosexual activity as an explanation for the clustering observed. Thus, the demography of HTLV-I was not accounted for comple tely by sexual and mother-to-offspring transmission. The predominance of clustering of unrelated HTLV-I-seropositive individuals in location s with high mosquito infestation raised the possibility of sporadic tr ansmission of HTLV-I by hematophagous insects.