Luis Rosero Bixby
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Item A population-based serosurveillance of syphilis in Costa Rica(Reprinted from Sexually Transmitted Diseases, Vol. 18, no. 2 (april-June 1991), 1991) Larsen, Sandra A.; Oberle, Mark W.; Sánchez Braverman, Juana M.; Rosero Bixby, Luis; Vetter, Kathleen M.As part of a case-control study to investigate the high incidence of cervical cancer in Costa Rican women, the seroprevalence of the trepnematoses, in particular, syphilis was determined. In each age group, women with a history of two or more sex partners were two to four times more likely to be seroreactive in tests for syphilis than women with zero or one sex partner. The highest percentage of reactive results in the microhemagglutination assay for antibodies to Trepnema pallidum (MHATP) was seen in samples from women aged 50-59 who had had two or more lifetime partners (23.8%). Three observations from our study support reactivity due to syphilis rather than yaws or pinta: ( /) a similar percent of reactive rapid plasma reagin (RPR) card test results among MHA-TP reactors in the two age groups of women who were surveyed (42 vs. 49%) was observed; (2) women who were seroreactive in the MHA-TP had multiple risk factors for STD (low socioeconomic status (9.4%), urban residence (22.8%), first intercourse under 16 years of age (14.1%), and multiple sex partners (26.3%)|, and (j) only sexually experienced women had reactive results in the MHA-TP test.Item A case-control study of breast cancer and hormonal contraception in Costa Rica(JNCI, vol. 7, no. 1 (december 1987), 1987) Lee, Nancy C.; Rosero Bixby, Luis; Oberle, Mark W.; Grimaldo, Carmen; Whatley, Anne S.; Rovira, Elizabeth Z.By 1981, 11% of married women in Costa Rica ages 20-49 years had used depot-medroxyprogesterone acetate (DMPA) and 58% had used oral contraceptives (OCs). Since 1977, the Costa Rican Ministry of Health has maintained a nationwide cancer registry. These circumstances provided an opportunity for a population-based, case-control study of DMPA, OCs, and breast cancer in Costa Rica. Cases were 171 women ages 25-58 years with breast cancer diagnosed between 1982 and 1984; controls were 826 women randomly chosen during a nationwide household survey. Cases and controls were interviewed with the use of a standard questionnaire covering their reproductive and contraceptive histories. Logistic regression methods were used to adjust for confounding factors. While few cases or controls had ever used DMPA, DMPA users had an elevated relative risk (RR) estimate of breast cancer of 2.6 (95% confidence limits = 1.4-4.7) compared with never users. However, no do'se-response relationship was found; even the group of women who had used DMPA for less than 1 year had an elevated RR estimate (RR = 2.3; 95% confidence limits = 1.0-5.1). In contrast, OC users had no elevation in RR compared with never users (RR = 1.2; 95% confidence limits= 0.8-1.8). The results of the DMPA analysis are inconclusive. Before decisions are made on whether to continue providing this effective contraceptive method, other ongoing studies will need to confirm of refute these findings.—JNCI 1987; 79:1247-1254.Item The effect of using different reference dates for control exposure measurement on relative risk estimates in a case-control study(Journal Clinical Epidemiologycal, Vol. 46, no. 5, 1993) Rampey, Alvin H.; Irwin, Kathleen L.; Oberle, Mark W.; Kinchen, Steven; Lee, Nancy C.; Marsden, Anne; Rosero Bixby, LuisArtículo científico -- Universidad de Costa Rica, Instituto de Investigaciones en Saud. 1993. Debido a las políticas de la revista en la que el artículo fue publicado, no es posible distribuir la edición del editor/PDF. In case-control studies in which case and control enrollment periods are not identical, exposure status for time-dependent variables is often measured relative to a reference date. Using data from a case-control study of the relation between cervical cancer and oral contraceptive (OC) use in which control enrollment began 6 months after the end of case enrollment, we evaluated the effect on odds ratios from using five different reference dates to determine the controls' exposure status. The choice of reference date had little effect on the odds ratios in this study. Reference dates for time-dependent exposure variables should be considered carefully in studies when case and control enrollment periods are not identical.