title: Tracing of patients lost to follow-up and HIV transmission: mathematical modeling study based on 2 large ART programs in Malawi.
abstract: OBJECTIVE
  Treatment as prevention depends on retaining HIV-infected patients in care. We investigated the effect on HIV transmission of bringing patients lost to follow-up (LTFU) back into care.
  
  
  METHODS
  Mathematical model.
  
  
  METHODS
  Stochastic mathematical model of cohorts of 1000 HIV-infected patients on antiretroviral therapy, based on the data from 2 clinics in Lilongwe, Malawi. We calculated cohort viral load (sum of individual mean viral loads each year) and used a mathematical relationship between viral load and transmission probability to estimate the number of new HIV infections. We simulated 4 scenarios: "no LTFU" (all patients stay in care), "no tracing" (patients LTFU are not traced), "immediate tracing" (after missed clinic appointment), and "delayed tracing" (after 6 months).
  
  
  RESULTS
  About 440 of 1000 patients were LTFU over 5 years. Cohort viral loads (million copies/mL per 1000 patients) were 3.7 [95% prediction interval (PrI), 2.9-4.9] for no LTFU, 8.6 (95% PrI, 7.3-10.0) for no tracing, 7.7 (95% PrI, 6.2-9.1) for immediate, and 8.0 (95% PrI, 6.7-9.5) for delayed tracing. Comparing no LTFU with no tracing, the number of new infections increased from 33 (95% PrI, 29-38) to 54 (95% PrI, 47-60) per 1000 patients. Immediate tracing prevented 3.6 (95% PrI, -3.3 to 12.8) and delayed tracing 2.5 (95% PrI, -5.8 to 11.1) new infections per 1000. Immediate tracing was more efficient than delayed tracing: to 116 and 142 tracing efforts, respectively, were needed prevent 1 new infection.
  
  
  CONCLUSIONS
  Tracing of patients LTFU enhances the preventive effect of antiretroviral therapy, but the number of transmissions prevented is small.
authors: *Institute of Social and Preventive Medicine (ISPM), University of Bern, Bern, Switzerland; †The International Union Against Tuberculosis and Lung Disease, Paris, France; ‡Lighthouse Trust, Lilongwe, Malawi; §Centre for Infectious Disease Epidemiology and Research, University of Cape Town, Cape Town, South Africa; ‖Department of Infectious Diseases, University Hospital Bern, Bern, Switzerland; ¶Department of Infectious Diseases, University of Dakar, Dakar, Senegal; #International Training and Education Center for Health, University of Washington, Seattle, WA.
authors: Janne
authors: J
authors: Estill
authors: Hannock
authors: H
authors: Tweya
authors: Matthias
authors: M
authors: Egger
authors: Gilles
authors: G
authors: Wandeler
authors: Caryl
authors: C
authors: Feldacker
authors: Leigh F
authors: LF
authors: Johnson
authors: Nello
authors: N
authors: Blaser
authors: Luisa Salazar
authors: LS
authors: Vizcaya
authors: Sam
authors: S
authors: Phiri
authors: Olivia
authors: O
authors: Keiser
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D044966:Anti-Retroviral Agents / Q000627:therapeutic use; D023241:Antiretroviral Therapy, Highly Active / Q000379:methods; D018562:Disease Transmission, Infectious / Q000517:prevention & control*; D005260:Female; D015658:HIV Infections / Q000188:drug therapy* / Q000517:prevention & control* / Q000635:transmission; D006801:Humans; D059012:Lost to Follow-Up; D008295:Malawi; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D019562:Viral Load; D055815:Young Adult
chemical_list: D044966:Anti-Retroviral Agents