Susan M Graham 1, Janet Raboud, R Scott McClelland, Walter Jaoko, Jeckoniah Ndinya-Achola, Kishor Mandaliya, Julie Overbaugh, Ahmed M Bayoumi
Affiliation
- 1Department of Medicine, University of Washington, Seattle, Washington, United States of America. grahamsm@u.washington.edu
PMID: 23555041 PMCID: PMC3595247
DOI: 10.1371/journal.pone.0059480
Abstract
Objective: Conventional survival estimates may be biased if loss to follow-up (LTF) is associated with the outcome of interest. Our goal was to assess whether the association between sexual risk behavior and HIV-1 acquisition changed after accounting for LTF with competing risks regression.
Methods: HIV-1-seronegative women who enrolled in a Kenyan sex worker cohort from 1993-2007 were followed prospectively and tested for HIV at monthly clinic visits. Our primary predictor was self-reported sexual risk behavior in the past week, analyzed as a time-dependent covariate. Outcomes included HIV-1 acquisition and LTF. We analyzed the data using Cox proportional hazards regression and competing risks regression, in which LTF was treated as a competing event.
Results: A total of 1,513 women contributed 4,150 person-years (py), during which 198 (13.1%) acquired HIV-1 infection (incidence, 4.5 per 100 py) and 969 (64.0%) were LTF (incidence, 23.4 per 100 py). After adjusting for potential confounders, women reporting unprotected sex with multiple partners were less likely to be lost to follow-up (adjusted sub-hazard ratio (aSHR) 0.50, 95% confidence interval (CI) 0.32-0.76, relative to no sexual activity). The risk of HIV-1 acquisition after reporting unprotected sex with multiple partners was similar with Cox regression (adjusted hazard ratio (aHR) 2.41, 95% CI 1.36-4.27) and competing risks regression (aSHR 2.47, 95% CI 1.33-4.58).
Conclusions: Unprotected sex with multiple partners was associated with higher HIV-1 acquisition risk, but lower attrition. This differential attrition did not substantially bias Cox regression estimates when compared to competing risks regression results.
Conflict of interest statement
Competing Interests: 1) Co-author SMG is currently a PLOS ONE editorial board member. This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials. 2) Dr. KM has acted as a consultant to the University of Washington research site in Mombasa, Kenya, for many years, and has most recently been employed by PathCare Laboratories. PathCare did not perform any laboratory testing related to this research, nor was this entity involved in any other way in the research. There are no patents, products in development, or marketed products that relate to this work. Dr. KM’s employment relationship with PathCare does not alter in any way the authors’ adherence to all the PLOS ONE policies on sharing data and materials.
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