INCIDENCE OF HTLV-I-ASSOCIATED MYELOPATHY TROPICAL SPASTIC PARAPARESIS (HAM TSP) IN JAMAICA AND TRINIDAD/

HTLV-I is sexually transmitted more efficiently from men to women than vice versa, and the majority of HTLV-I endemic areas report a female preponderance of HTLV-I-associated myelopathy/tropical spastic parapar esis (HAM/TSP) cases. The objective of this study was to estimate the gender-and age specific incidence rates of HAM/TSP in the general popu lation as well as in the HTLV I-infected population in Jamaica and in Trinidad and Tobago. Incidence rates for HAM/TSP were computed based o n all reported incident cases in both countries between 1990 and 1994. Population census reports for 1990 were used to calculate the populat ion at risk, The age-standardized HAM/TSP incidence rate (mean +/- sta rdard error of the mean) in Jamaica was 1.8 +/- 0.2/100,000 person yea rs (PY). Among individuals of African descent in Trinidad and Tobago, the rate was 1.7 +/- 0.4/100,000 PY. As in HTLV-I seroprevalence, the incidence rate of HAM/TSP increased with age through the fifth decade of life and was three times as high in women than in men. The HAM/TSP incidence rate, calculated as a function of the number of HTLV-I-infec ted persons in each age stratum, is higher in women (24.7/100,000 PY) than in men (17.3/100,000 PY). With HTLV-I infection, the lifetime ris k of developing HAM/TSP was estimated to be 1.9% overall and is slight ly higher in women (1.8%) than in men (1.3%). Thus, the higher prevale nce of HTLV-I in women in endemic areas does not fully explain the pre ponderance of female HAM/TSP, suggesting that other cofactors must be present. The higher incidence rate in women between the ages of 40 and 59 years, as well as the increase in HAM/TSP incidence rates with age , are indicative of the importance of adult-acquired HTLV-I infection, presumably through sexual transmission.