We found HTLV-1 infection in nearly 2% (95% CI, 1.2–2.2) of women seeking prenatal, delivery, or abortion services in a large public hospital in Lima, Peru. Similar levels of HTLV-1 have been reported among pregnant women and other obstetric and gynecologic patients in Jamaica (3.5%), Martinique (1.9%), and Brazil (0.8%).13–15
Our findings are also consistent with the 3.1% (95% CI, 1.6–4.6) prevalence observed among women attending a public prenatal clinic in Lima during the 1980s.7
More recently, Sanchez-Palacios et al10
reported prevalence ranging from 1.3% to 3.8% among women in 3 different regions of Peru. Neither of these previous studies, however, evaluated the relative importance of the different routes by which HTLV-1 is transmitted. This large, cross-sectional study enabled the comparison of HTLV-1 prevalence across age and regional birth cohorts, while taking into account risk factors for adult acquisition of infection.
We found increasing age and earlier age at first sexual intercourse to be the strongest and independent risk factors for HTLV-1 infection. These risk factors are likely surrogates for numbers of exposures to an infected partner. Early onset of sex by females might also hypothetically be associated with greater susceptibility to acquisition of HTLV-1. Age-related increases in HTLV-1 prevalence have been observed consistently in endemic populations.16,17
The increase is typically more pronounced in women, suggesting more efficient sexual transmission from man to woman than the reverse. A prospective study of 97 heterosexual couples serodiscordant for HTLV-1 infection found a 4-fold greater incidence among initially seronegative wives than among husbands.18
A more recent study reported a smaller and nonstatistically significant excess for man-to-woman transmission, but it included only 30 couples and had a high loss to follow-up (45%).19
It is of interest that women who indicated a history of abortion were more likely to be HTLV-1 seropositive. Because induced abortion is illegal in Peru, it was not considered possible to elicit an accurate history of this procedure. Indeed, the relationship was of borderline statistical significance and attenuated by adjustment for other risk factors. Abortion also was associated with HIV in the cohort from which this study sample was derived.11
Information regarding the circumstances leading to abortion will be required to interpret the nature of this association. It has been estimated that each year, 5.2% of Peruvian women aged 15 to 49 years are likely to have an abortion.20
Transfusion with contaminated blood appears to have been a relatively uncommon route of transmission in our population but may have played a more important role in other regions. We detected infection in 5.5% of the 4% of participants with a history of blood transfusion. In a comparable study by Sanchez-Palacios et al,10
predominantly involving women in the Andean city of Huanta, HTLV-1 was detected in 13.6% of the 10% of women with this history. Interestingly, dental and other surgery, but not transfusion, were strongly associated with HTLV-1 infection among 211 pregnant women surveyed by Zurita et al9
in the Andean city of Quillabamba. These differences in risk may reflect regional differences in blood donation and screening practices. In a national survey conducted in 1997, 1.3% of blood donors were HTLV-1 seropositive by ELISA.21
Women born in the Andes were no more likely to be HTLV-1 seropositive than were those born in other regions of the country. This is consistent with the findings from the only population-based study conducted in Peru.10
The association between Andean birth and HTLV-1 infection observed in other studies may best be explained by selection bias and known behavioral risk factors.9,22
Similarly, although we found some evidence that women born in Lima may be at particularly high risk of infection, this relationship was of borderline statistical significance and did not remain in our final model which adjusted for risk factors operating during adulthood.
Conclusions about risk factors for incident infection are limited by the cross-sectional design of this study. Neonatal exposure to infection may have decreased over the represented birth cohorts, either due to changes in breast-feeding practices or prevalence in the maternal generation. Conclusions about prevalence by birth region must consider the possibility that our study participants differ from individuals who did not migrate to Lima. In addition, caution must be used in extrapolating our findings to the general population of Peru or even subsets such as all pregnant women in the same geographic region. As has been observed for HIV, selection bias may arise from factors associated with fertility (e.g., age, sexual behavior, contraceptive use) or clinic attendance (e.g., education level, geographic mobility).23,24
However, in a pair of studies from Salvador, Brazil prevalence of HTLV-1 infection among women presenting for prenatal care was quite comparable to that among similar aged women in a citywide population sample.15,25
Prevalence among pregnant women in Europe was consistently greater than that among blood donors, but the latter group might be expected to underestimate prevalence relative to the general population.26
Finally, it is possible that our strategy of testing pooled specimens may have reduced the sensitivity for detecting HTLV-1 infection.27
However, it is unlikely that any inaccuracy would be related to the risk factors under investigation.
Nearly 2% of the women in this study had HTLV-1 infection. This is an important indicator of the potential for sustained and endemic transmission in the general population. Our observations suggest HTLV-1 is maintained in Peru by a low level of neonatally acquired infection that is amplified by sexual transmission. The lack of geographic associations indicates prevention efforts must be broad based. Peru instituted universal screening of blood donors in 1997.28
Counseling of HTLV-1 seropositive blood donors should include education regarding how to avoid transmitting the virus and might incorporate identification and testing of family members and sexual contacts. Safer sex messages directed at limiting transmission of HIV and other STIs should include HTLV-1 as a target. Finally, programs should be developed to reduce neonatal transmission. Peru’s 2000 national health survey found over 90% of infants younger than 9 months were breast-fed, and the median duration of breast-feeding was greater than 22 months.29
Epidemiological data indicate that the risk of infection is greatest for children breast-feeding after 12 months of age, and transmission might be greatly reduced if HTLV-1 infected mothers avoid or limit duration of breast-feeding.30