Conditional Cash Transfers to Incentivize Tuberculosis Screening: Description of a Novel Strategy for Contact Investigation in Rural South Africa

Abstract

Background: Providing incentives to screen close contacts for tuberculosis (TB) is an alternative to household-based contact investigation. We aimed to characterize patients and contexts where this incentive-based strategy might be preferred.

Methods: This is a secondary analysis of a cluster randomized trial of TB contact investigation in Limpopo District, South Africa, conducted between 2016 and 2020. Twenty-eight clinics were randomly allocated to household-based vs incentive-based contact investigation. In the incentive-based arm, index participants and contacts received transport reimbursement and incentives for TB screening and microbiological diagnosis of contacts. We estimated differences in mean number of contacts per index participant with household-based vs incentive-based contact investigation overall and within subgroups of index participants.

Results: A total of 3776 contacts (1903 in the incentive-based and 1873 in the household-based arm) were referred by 2501 index participants. A higher proportion of contacts in the incentive-based than household-based arm were adults (72% vs 59%), reported chronic TB symptoms (25% vs 16%) or ever smoking (23% vs 11%). Index participants who walked or bicycled to a clinic referred 1.03 more contacts per index (95% confidence interval [CI], .48 to 1.57) through incentive-based than household-based investigation. Index participants living with >5 household members referred 0.48 more contacts per index (95% CI, .03 to .94) through household-based than incentive-based investigation.

Conclusions: Relative to household-based investigation, incentive-based investigation identifies contacts likely at higher risk for active TB. Incentive-based investigation may be more appropriate for index participants who can easily access clinics, versus household-based investigation for patients with large households. Clinical Trials Registration. NCT02808507.

Keywords: contact tracing; incentive; index patient epidemiology; motivation; tuberculosis.

Figure 1.

Study flow diagrams. The left side of the figure shows the population in the incentive-based contact investigation arm, and the right side shows the population in the household contact investigation arm. Numbers differ slightly from those in the primary report of intervention effectiveness (Hanrahan et al, under review) in that only those contacts who completed the study interview were included in the current analysis. Abbreviation: MTB/RIF, Mycobacterium tuberculosis/rifampin.

Figure 2.

Distribution of number of contacts among participants diagnosed with tuberculosis (“index participants”). The left panel shows the distribution of the number of contacts referred by each index participant in the incentive-based contact investigation arm, while the right panel shows the corresponding distribution in the household contact investigation arm. The distribution is split by districts—Waterberg (periurban) in light grey and Vhembe (rural) in dark grey. The overall mean number of contacts referred per case was similar between the 2 arms: 2.43 (95% confidence interval [95% CI], 2.18 to 2.69) in the incentive-based arm vs 2.33 (95% CI, 2.15 to 2.51) in the household-based arm. However, the proportion of index participants referring either zero (55% vs 34%) or ≥10 contacts (11% vs 3%) was higher in the incentive-based arm. By district, the proportion of index participants referring either zero or ≥10 contacts was higher in Waterberg than in Vhembe for both arms.

Figure 3.

Number of contacts identified per index participant according to index characteristics. A, Lightly shaded squares (bars) show the point estimate (95% confidence interval [95% CI]) for the number of contacts identified per index participant in the incentive-based arm, whereas darkly shaded circles show corresponding values in the household-based arm. Only the subgroups whose mean difference in the mean number of contacts per index case between arms (in at least 1 category) was greater than 0.50 are shown in this figure. Another figure showing this difference according to all measured index participant characteristics is in the Supplementary Materials. B, The difference in mean number of contacts per index participant (ie, value of lightly shaded squares minus darkly shaded circles). In this figure, numbers larger than zero indicate that the mean number of contacts per index participant among participants of a given subgroup is higher in the incentive-based arm than in the household-based arm.