Estimating the seroprevalence of HTLV-1 in pregnant Peruvian women based on blood bank markers: a road to elimination of mother-to-child transmission of HTLV-1 in Peru

Background: Data regarding the burden of human T-cell lymphotropic virus type 1 (HTLV-1) in pregnant Peruvian women is scarce, thus the impact of potential preventive interventions is largely unknown. Our primary aim was to estimate the prevalence of HTLV-1 in pregnant women in Peru at national and departmental levels using governmental-issued blood bank data. In addition, the number of newborns with HTLV-1 acquired yearly via mother-to-child-transmission (MTCT) was calculated. Methods: This was a retrospective ecological cohort study conducted at the level of department-year for the period 2015-2020. Publicly available data maintained by Peruvian governmental organizations was used. The unit of analysis were the 25 first-level administrative subdivisions of Peru known as departments. An analytic strategy that included correction factors, probabilistic weights and small-area estimation modeling was developed to extrapolate HTLV-1/2 reactivity in blood donors to confirmatory HTLV-1 reactivity in pregnant women. For validation, confirmatory HIV reactivity in pregnant women was estimated using the same data and methods and was compared to official statistics. Results: Between 2015 and 2020, a total of 2,120,344 blood units were screened of which 15,413 (0.73%) were reactive for HTLV-1/2. We estimated there were 4,602 [95% CI: 3,851-5368] pregnant Peruvian women with HTLV-1 per year during 2015-2020 and this represented a confirmatory HTLV-1 reactivity of 1.05% [95% CI: 0.88-1.23]. A total of 12 departments had an estimated confirmatory HTLV-1 prevalence in pregnant women of 1% or higher and a tendency towards higher values in the southern departments was visualized. We noted a strong spatial pattern of our estimates (phi = 49%) and an acceptable degree of precision as most of our department-level estimates had a coefficient of variation (CV) of less than 30%. For newborns, we estimated 115 [95% CI: 96-134] cases of HTLV-1 acquired yearly in-utero and 1,009 [95% CI: 920-1,282] cases of HTLV-1 acquired yearly due to breastfeeding. Our estimates for confirmatory HIV reactivity in pregnant Peruvian women were comparable to international and national statistics. Conclusion: Our estimates demonstrated a high burden of HTLV-1 in pregnant Peruvian women and provided critical information needed for the evaluation of HTLV-1 MTCT preventive interventions such as avoidance breastfeeding and formula supplementation. We demonstrated our analytic strategy generated estimates with a fair degree of precision and accuracy, however the potential for underestimation, variability within some departments, and need for population-based studies should be recognized.