Browsing by Author "Westfall, Andrew O"

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    Open Access
    Estimating loss to follow-up in HIV-infected patients on antiretroviral therapy: the effect of the competing risk of death in Zambia and Switzerland
    (Public Library of Science, 2011) Schöni-Affolter, Franziska; Keiser, Olivia; Mwango, Albert; Stringer, Jeffrey; Ledergerber, Bruno; Mulenga, Lloyd; Bucher, Heiner C; Westfall, Andrew O; Calmy, Alexandra; Boulle, Andrew; Chintu, Namwinga; Egger, Matthias; Chi, Benjamin H
    BACKGROUND: Loss to follow-up (LTFU) is common in antiretroviral therapy (ART) programmes. Mortality is a competing risk (CR) for LTFU; however, it is often overlooked in cohort analyses. We examined how the CR of death affected LTFU estimates in Zambia and Switzerland. Methods and FINDINGS: HIV-infected patients aged ≥18 years who started ART 2004-2008 in observational cohorts in Zambia and Switzerland were included. We compared standard Kaplan-Meier curves with CR cumulative incidence. We calculated hazard ratios for LTFU across CD4 cell count strata using cause-specific Cox models, or Fine and Gray subdistribution models, adjusting for age, gender, body mass index and clinical stage. 89,339 patients from Zambia and 1,860 patients from Switzerland were included. 12,237 patients (13.7%) in Zambia and 129 patients (6.9%) in Switzerland were LTFU and 8,498 (9.5%) and 29 patients (1.6%), respectively, died. In Zambia, the probability of LTFU was overestimated in Kaplan-Meier curves: estimates at 3.5 years were 29.3% for patients starting ART with CD4 cells <100 cells/µl and 15.4% among patients starting with ≥350 cells/µL. The estimates from CR cumulative incidence were 22.9% and 13.6%, respectively. Little difference was found between naïve and CR analyses in Switzerland since only few patients died. The results from Cox and Fine and Gray models were similar: in Zambia the risk of loss to follow-up and death increased with decreasing CD4 counts at the start of ART, whereas in Switzerland there was a trend in the opposite direction, with patients with higher CD4 cell counts more likely to be lost to follow-up. CONCLUSIONS: In ART programmes in low-income settings the competing risk of death can substantially bias standard analyses of LTFU. The CD4 cell count and other prognostic factors may be differentially associated with LTFU in low-income and high-income settings.
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    Health facility characteristics and their relationship to coverage of PMTCT of HIV services across four African countries: the PEARL study
    (Public Library of Science, 2012) Ekouevi, Didier K; Stringer, Elizabeth; Coetzee, David; Tih, Pius; Creek, Tracy; Stinson, Kathryn; Westfall, Andrew O; Welty, Thomas; Chintu, Namwinga; Chi, Benjamin H
    BACKGROUND: Health facility characteristics associated with effective prevention of mother-to-child transmission of HIV (PMTCT) coverage in sub-Saharan are poorly understood. METHODOLOGY/PRINCIPAL FINDINGS: We conducted surveys in health facilities with active PMTCT services in Cameroon, Cote d'Ivoire, South Africa, and Zambia. Data was compiled via direct observation and exit interviews. We constructed composite scores to describe provision of PMTCT services across seven topical areas: antenatal quality, PMTCT quality, supplies available, patient satisfaction, patient understanding of medication, and infrastructure quality. Pearson correlations and Generalized Estimating Equations (GEE) to account for clustering of facilities within countries were used to evaluate the relationship between the composite scores, total time of visit and select individual variables with PMTCT coverage among women delivering. Between July 2008 and May 2009, we collected data from 32 facilities; 78% were managed by the government health system. An opt-out approach for HIV testing was used in 100% of facilities in Zambia, 63% in Cameroon, and none in Côte d'Ivoire or South Africa. Using Pearson correlations, PMTCT coverage (median of 55%, (IQR: 33-68) was correlated with PMTCT quality score (rho = 0.51; p = 0.003); infrastructure quality score (rho = 0.43; p = 0.017); time spent at clinic (rho = 0.47; p = 0.013); patient understanding of medications score (rho = 0.51; p = 0.006); and patient satisfaction quality score (rho = 0.38; p = 0.031). PMTCT coverage was marginally correlated with the antenatal quality score (rho = 0.304; p = 0.091). Using GEE adjustment for clustering, the, antenatal quality score became more strongly associated with PMTCT coverage (p<0.001) and the PMTCT quality score and patient understanding of medications remained marginally significant. Conclusions/RESULTS: We observed a positive relationship between an antenatal quality score and PMTCT coverage but did not identify a consistent set of variables that predicted PMTCT coverage.
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    Universal Definition of Loss to Follow-Up in HIV Treatment Programs: A Statistical Analysis of 111 Facilities in Africa, Asia, and Latin America
    (Public Library of Science, 2011) Chi, Benjamin H; Yiannoutsos, Constantin T; Westfall, Andrew O; Newman, Jamie E; Zhou, Jialun; Cesar, Carina; Brinkhof, Martin W G; Mwango, Albert; Balestre, Eric; Carriquiry, Gabriela
    Background: Although patient attrition is recognized as a threat to the long-term success of antiretroviral therapy programs worldwide, there is no universal definition for classifying patients as lost to follow-up (LTFU). We analyzed data from health facilities across Africa, Asia, and Latin America to empirically determine a standard LTFU definition. Methods and Findings: At a set ''status classification'' date, patients were categorized as either ''active'' or ''LTFU'' according to different intervals from time of last clinic encounter. For each threshold, we looked forward 365 d to assess the performance and accuracy of this initial classification. The best-performing definition for LTFU had the lowest proportion of patients misclassified as active or LTFU. Observational data from 111 health facilities - representing 180,718 patients from 19 countries - were included in this study. In the primary analysis, for which data from all facilities were pooled, an interval of 180 d (95% confidence interval [CI]: 173–181 d) since last patient encounter resulted in the fewest misclassifications (7.7%, 95% CI: 7.6%–7.8%). A secondary analysis that gave equal weight to cohorts and to regions generated a similar result (175 d); however, an alternate approach that used inverse weighting for cohorts based on variance and equal weighting for regions produced a slightly lower summary measure (150 d). When examined at the facility level, the best-performing definition varied from 58 to 383 d (mean = 150 d), but when a standard definition of 180 d was applied to each facility, only slight increases in misclassification (mean = 1.2%, 95% CI: 1.0%–1.5%) were observed. Using this definition, the proportion of patients classified as LTFU by facility ranged from 3.1% to 45.1% (mean = 19.9%, 95% CI: 19.1%–21.7%). Conclusions: Based on this evaluation, we recommend the adoption of $180 d since the last clinic visit as a standard LTFU definition. Such standardization is an important step to understanding the reasons that underlie patient attrition and establishing more reliable and comparable program evaluation worldwide.