Selection bias may have affected the validity of my analysis. Persons who were selected into the original sample but did not participate may have differed systematically from those who did
participate. Women who were selected were more likely to participate than men, but this is unlikely to bias most of our findings since analyses were conducted separately by sex. Residents of Punta Piedra and Cusuna were also less likely to participate, but non-participation at those sites appeared to be largely due to general challenges in study implementation rather than widespread refusal or absence of the selected individuals. However, this non-response resulted in an under-representation of persons from those sites and residents of rural areas. It is difficult to determine whether most of or structural or behavioral indicators of interest or disease outcomes differ systematically within these communities compared to the rest of the sample, due to the small sample reached (n=23). Perhaps more significantly, these findings may have underestimated the true underlying frequency and as migrants may have been less likely to identified and participate in the study. Those who were gone for longer durations (among whom there was an increased prevalence of having multiple sexual partnerships) may have been especially subject to non-participation as the longer duration away from their residence decreased the likelihood that a repeat visit would have resulted in successful
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Concurrency may have been misclassified, especially given the large number of observations for which sufficient data was not available to determine whether partnerships were concurrent (36/106 total persons reporting multiple sexual partnerships in the last 12 months). Concurrency is
acknowledged as a difficult indicator to measure; the limitations of even recently standardized definitions (106) have been documented (60,107). While many participants with concurrent partnerships reported long periods of overlap that are unlikely to succumb to measurement error, concurrency may be underestimated when measured only through dates of first and last sexual contact, and particularly among younger individuals (108). A direct question about whether sexual relations occurred with one partner between first and last sex with a second partner is typically recommended in addition to the assessment of dates of each partnership, but the study staff were apprehensive about the potential offensiveness of this question and did not believe it would be easily comprehended. These data are also right-censored, in that we failed to capture partnerships that had the potential to be concurrent if sexual contact was resumed with two or more former partners, but we opted to maintain a conservative estimate rather than assume the participants expectations of future sexual relations would definitely result in concurrent partnerships. There may be systematic
underreporting of multiple and concurrent partnerships among women and either overreporting or underreporting among men (60) due to social desirability bias, but it is unknown whether
misclassification of these outcomes would be related to individual migration history and in what direction this might bias results.
The validity of all diagnostic tests used to determine HIV, HSV-2, and STI status are subject to limitations. It is unlikely that HIV status was misclassified based on the multi-step protocol used to verify positive and negative tests, including pooled RNA analysis that could detect the presence of virus in the acute phase of infection when rapid antibody tests may still yield consistently negative test results. It is more likely that the HerpesSelect test may have yielded more false positives than false negatives given its typical performance within and outside of Latin America (97–99), which would have resulted in an overestimate of HSV-2 prevalence. The syphilis diagnostic process may have produced false positives if periodontal disease was prevalent in this population, as the TPPA assay is
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sensitive to other treponemes. However, the low specificity may not have biased our findings much given the low prevalence of syphilis observed in the population. It is assumed that the accuracy of the tests for Chlamydia, trichomoniasis, and M. genitalium did not vary systematically with participant characteristics.
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Table 3.1: Summary of diagnostic testing protocol for biological outcomes used in Aim 2.
Pathogen Specimen
Type of Test
Name, Brand
(as applicable) Sensitivity Specificity
Where test conducted Where quality control conducted HIV
Serum Rapid test(s)
1) Determine, Abbot 2) OraQuick, OraSure Determine: 100% OraQuick:98.1% (109) Determine: 98.9% OraQuick:100% (109)
Field Site N/A
Serum ELISA* Genscreen ULTRA HIV Ag-Ab Assay,
Bio-Rad
100%†
(110,111) 94.9-100% (110,111) NRLH NHIVL
Serum Western Blot** HIV BLOT 2.2, MP Diagnostics 94.9-100% (112) 100% (112) NRLH
HSV-2 Serum IgG ELISA HerpesSelect, Focus 93.8-100% (97–99) 60.4-94.0% (97–99) NRLH CDC Syphilis Serum RPR Macro-Vue, BD Microbiology Systems 73-100%§ (113,114) 93-99% (113,114) NRLH CDC Syphilis Serum
TPPA Serodia, Fujirebio, Inc 88-100% (115,116) 95-100% (115,116) NRLH CDC
C. trachomatis Urine (men)
Vaginal swab (women)
NAAT with RT-PCR
LCGP CDC,
NRLH
T. vaginalis Urine (men)
Vaginal swab (women)
NAAT with RT-PCR
LCGP CDC,
NRLH
M. genitalium Urine (men)
Vaginal swab (women)
NAAT with RT-PCR
LCGP CDC,
NRLH *Conducted on all serum samples, regardless of rapid test results at field site
**Conducted on all samples collected from individuals with inconclusive ELISA results † Sensitivity among non-acute cases
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