Temporal trends in Human T-Lymphotropic virus 1 (HTLV-1) associated myelopathy/tropical spastic paraparesis (HAM/TSP) incidence in Martinique over 25 years (1986-2010)

Background: Human T-lymphotropic virus type 1 (HTLV-1) has been discovered in 1980 and has been linked to tropical spastic paraparesis (HAM/TSP) in 1985 in Martinique. There is no data on HAM/TSP incidence trends. We report, in the present work, the temporal trends incidence of HAM/TSP in Martinique over 25 years. Methods: Martinique is a Caribbean French West Indies island deserved by a unique Neurology Department involved in HAM/TSP diagnosis and management. A registry has been set up since 1986 and patients diagnosed for a HAM/TSP were prospectively registered. Only patients with a definite HAM/TSP onset between 1986 and 2010 were included in the present study. The 25-year study time was stratified in five-year periods. Crude incidence rates with 95% confidence interval (95%CI) were calculated using Poisson distribution for each period. Age-standardized rates were calculated using the direct method and the Martinique population census of 1990 as reference. Standardized incidence rate ratios with 95% CIs and P trends were assessed from simple Poisson regression models. Number of HTLV-1 infection among first-time blood donors was retrospectively collected from the central computer data system of the Martinique blood bank. The HTLV-1 seroprevalence into this population has been calculated for four 5-year periods between 1996 and 2015. Results: Overall, 153 patients were identified (mean age at onset, 53+/-13.1 years; female:male ratio, 4:1). Crude HAM/TSP incidence rates per 100,000 per 5 years (95%CI) in 1986–1990, 1991–1995, 1996–2000, 2001–2005 and 2006–2010 periods were 10.01 (6.78–13.28), 13.02 (9.34–16.70), 11.54 (8.13–14.95), 4.27 (2.24–6.28) and 2.03 (0.62–3.43). Age-standardized 5-year incidence rates significantly decreased by 69% and 87% in 2001–2005 and 2006–2010 study periods. Patients characteristics did not differ regarding 1986–2000 and 2001–2010 onset periods. Between 1996–2000 and 2011–2015 study periods, the HTLV-1 seroprevalence significantly decreased by 63%. Conclusion: Martinique faces a sudden and rapid decline of HAM/TSP incidence from 2001 in comparison to 1986–2000 periods. Reduction of HTLV-1 seroprevalence, that may result from transmission prevention strategy, could account for HAM/TSP incidence decrease. Author summary: Human T-lymphotropic virus type 1 (HTLV-1) was discovered in 1980 and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) was described five years later in 1985. HAM/TSP is a progressive disabling disorder characterized by spastic paraparesis with bladder and bowel dysfunction that constitutes a significant public health problem in endemic areas. Up to date, there is no efficiency treatment of HAM/TSP and prevention of HTLV-1 transmission is critical to limit the disease spreading throughout communities. In the present 25-year-study time, we report a significant decrease of HAM/TSP incidence estimated more than 70% in early 2000 compared to 1986–2000 period in Martinique a French West Indies Island. We found a trend to a significant older age at onset after 2000 (52.1 years versus 57.5 years, p = 0.06) that may reflect an age cohort effect and that could be indicative of a rapid decrease in HTLV-1 seroprevalence. We showed a significant decline in HTLV-1 infection among first-time blood donors between 1996–2000 and 2011–2015 study periods. Thus, probable HTLV-1 seroprevalence decrease secondary to HTLV-1 antibodies screening in blood donors and pregnant women and to iterative information campaigns could partly account for HAM/TSP incidence decline. This study emphasizes the importance of prevention strategies to control HAM/TSP development in HTLV-1 endemic areas.