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. 2022 Feb 23;35(2):e00078-21. doi: 10.1128/cmr.00078-21

TABLE 3.

Risk factors for HTLV-1 transmission

Transmission route Risk factor (references)
Maternal exposure Breastfeeding duration, particularly longer than 6 mo (116, 239244)
Higher maternal HTLV-1 proviral load (234, 245247, 249, 250)
Sexual intercourse Condomless sex (254)
Earlier age at first sex (262)
No. of partners (261)
Current or past sexually transmissible infections (102, 254, 258, 259, 261, 468)a
Sex during menses and vaginal douching pre- and postintercourse (102)
Higher HTLV-1 proviral load (253, 254, 256, 257)
Duration of sexual relationship (253, 254)
Therapeutic use of blood products Shorter storage duration (266, 268, 269)
a

It is difficult to distinguish sexually transmitted infections as a cofactor for HTLV-1 transmission from the alternative explanation that both HTLV-1 and other sexually transmitted infections are driven by sexual behavior as the common causal factor.