Mortality among adults transferred and lost to follow-up from antiretroviral therapy programmes in South Africa: a multicentre cohort study.
Jun 24 2014
BACKGROUND & OBJECTIVES: Little is known about outcomes after transfer out (TFO) and loss to follow-up (LTF) and how differential outcomes might bias mortality estimates, as analyses generally censor or exclude TFOs/LTF. Using data linked to the National Population Register (NPR), we explored mortality among patients TFO and LTF compared with patients retained and investigated how linkage impacted on mortality estimates.
METHODS: A cohort analysis of routine data on adults with civil-identification numbers starting ART 2004-2009 in four large South African ART cohorts. The number, proportion, timing and mortality of TFOs and LTF were reported. Mortality was compared using Kaplan-Meier curves, Cox's proportional hazards and competing risks regression.
RESULTS: Before linkage, 1207 patients (6%) had died, 2624 (13%) were LTF, 1067 (5%) were TFO and 14583 (75%) were retained. Compared with retained, mortality risk was three times higher among TFOs (aHR 3.11, 95% CI 2.42-3.99) and 20 times higher among LTF patients (aHR 22.03, 95% CI 20.05-24.21). Excluding early deaths after TFO or LTF, the risk was comparable among TFOs and retained (aHR 0.75, 95% CI 0.54-1.03) and higher among LTF (aHR 2.85, 95% CI 2.43-3.33). After linkage, corrected mortality was higher than site-reported mortality. Censoring did not however lead to substantial underestimation of mortality among TFOs.
CONCLUSIONS: While TFO and LTF predicted mortality, the lower incidence of TFO and subsequent death compared with LTF meant that censoring TFOs did not bias mortality estimates. Future cohort analyses should explicitly consider proportions TFO/LTF and mortality event rates.