title: Survival functions for defining a clinical management Lost To Follow-Up (LTFU) cut-off in Antiretroviral Therapy (ART) program in Zomba, Malawi.
abstract: While, lost to follow-up (LTFU) from antiretroviral therapy (ART) can be considered a catch-all category for patients who miss scheduled visits or medication pick-ups, operational definitions and methods for defining LTFU vary making comparisons across programs challenging. Using weekly cut-offs, we sought to determine the probability that an individual would return to clinic given that they had not yet returned in order to identify the LTFU cut-off that could be used to inform clinical management and tracing procedures.
  
  
  
  Individuals who initiated ART with Dignitas International supported sites (n = 22) in Zomba, Malawi between January 1 2007-June 30 2010 and were ≥ 1 week late for a follow-up visit were included. Lateness was categorized using weekly cut-offs from ≥1 to ≥26 weeks late. At each weekly cut-off, the proportion of patients who returned for a subsequent follow-up visit were identified. Cumulative Distribution Functions (CDFs) were plotted to determine the probability of returning as a function of lateness. Hazard functions were plotted to demonstrate the proportion of patients who returned each weekly interval relative to those who had yet to return.
  
  
  
  In total, n = 4484 patients with n = 7316 follow-up visits were included. The number of included follow-up visits per patient ranged from 1-10 (median: 1). Both the CDF and hazard function demonstrated that after being ≥9 weeks late, the proportion of new patients who returned relative to those who had yet to return decreased substantially.
  
  
  
  We identified a LTFU definition useful for clinical management. The simple functions plotted here did not require advanced statistical expertise and were created using Microsoft Excel, making it a particularly practical method for HIV programs in resource-constrained settings.
authors.affiliation: The Ontario HIV Treatment Network, Toronto, Canada.|Division of Clinical Public Health, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada.
authors.forename: Beth
authors.initials: B
authors.lastname: Rachlis
authors.affiliation: Division of Clinical Public Health, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada.|Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada.
authors.forename: Donald C
authors.initials: DC
authors.lastname: Cole
authors.affiliation: Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada. m.vanlettow@dignitasinternational.org.|Dignitas International, Zomba, Malawi. m.vanlettow@dignitasinternational.org.
authors.forename: Monique
authors.initials: M
authors.lastname: van Lettow
authors.affiliation: Division of Biostatistics, Dalla Lana School of Public Health, University of Toronto, Toronto, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Escobar
mesh_terms: D023241:Antiretroviral Therapy, Highly Active / Q000706:statistics & numerical data*; D003695:Delivery of Health Care / Q000458:organization & administration / Q000706:statistics & numerical data*; D015658:HIV Infections / Q000188:drug therapy*; D006801:Humans; D008295:Malawi; D016019:Survival Analysis; D016903:Drug Monitoring
keywords: Antiretroviral therapy; HIV/AIDS; Malawi; Retention; Survival functions