Table 1

Base case inputs and distributions

Baseline probability of disengagement from clinic per day (without intervention)*
Months in care

Relative risk of disengaging from clinic, intervention versus no intervention0.78Lognormal (−0.25, 0.08)8
Daily probability of disengaged patients who were successfully traced†0.0025Beta (1745,  426)12 14 15 17 38
Proportion of those successfully traced, found alive and not in care who returned to care0.55Beta (505,  414)12 15 17 18
Cost of intervention 
 Risk reduction
Range: $2.50–17.50
Range: 1.14–7.98
Cost of adding one additional participant to the study: includes fixed costs$114031–34
Lifetime of the intervention10 yearsAssumption
Effective population‡
 Risk reduction
950 000
418 000
4 35
Willingness to pay per quality-adjusted life-years$2473$1377–413027 39
  • *The baseline daily probability of disengagement depends on the number of months in continuous care. When a patient re-engages in care after a period of disengagement, the months in care is reset to zero.

  • †The baseline rate of re-engagement is not an input rather calculated by the model. On average, 3.7% of disengaged patients who do not receive the outreach intervention will return to care in a lifetime. Without intervention, we assume that patients return to care if their clinical status is WHO stage 4 to reflect the idea that very sick patients are more likely to seek care.

  • ‡The effective population for the risk reduction intervention includes adults on antiretroviral therapy (596 228 as reported by the Kenyan Ministry of Health in 2014) plus adults in pre-antiretroviral therapy care (354 633= (1 402 212–596 228)*0.44. An estimated 1 402 212 adults are HIV-positive in Kenya as reported in 2014 by the Kenyan Ministry of Health. The 44% figure comes from a systematic review in which it was reported that the median proportion of patients enrolling in care after testing HIV-positive was 44%.4 The effective population for the outreach intervention is the number of adults on antiretroviral therapy and in pre-antiretroviral therapy care.

  • All dollars are in 2015 US currency.