Cost-effectiveness of chagas disease vector control strategies in Northwestern Argentina

Abstract

Background: Control and prevention of Chagas disease rely mostly on residual spraying of insecticides. In Argentina, vector control shifted from a vertical to a fully horizontal strategy based on community participation between 1992 and 2004. The effects of such strategy on Triatoma infestans, the main domestic vector, and on disease transmission have not been assessed.

Methods and findings: Based on retrospective (1993-2004) records from the Argentinean Ministry of Health for the Moreno Department, Northwestern Argentina, we performed a cost-effectiveness (CE) analysis and compared the observed CE of the fully horizontal vector control strategy with the expected CE for a vertical or a mixed (i.e., vertical attack phase followed by horizontal surveillance) strategy. Total direct costs (in 2004 US$) of the horizontal and mixed strategies were, respectively, 3.3 and 1.7 times lower than the costs of the vertical strategy, due to reductions in personnel costs. The estimated CE ratios for the vertical, mixed and horizontal strategies were US$132, US$82 and US$45 per averted human case, respectively. When per diems were excluded from the costs (i.e., simulating the decentralization of control activities), the CE of vertical, mixed and horizontal strategies was reduced to US$60, US$42 and US$32 per averted case, respectively.

Conclusions and significance: The mixed strategy would have averted between 1.6 and 4.0 times more human cases than the fully horizontal strategy, and would have been the most cost-effective option to interrupt parasite transmission in the Department. In rural and dispersed areas where waning vertical vector programs cannot accomplish full insecticide coverage, alternative strategies need to be developed. If properly implemented, community participation represents not only the most appealing but also the most cost-effective alternative to accomplish such objectives.

Figure 1. Long-term effects of the fully horizontal strategy.

(A) Domestic and peridomestic prevalence of infestation by Triatoma infestans (bars) and number of rural houses sprayed during 1993–2004 (line) in Moreno Department. Numbers on top of bars represent the total number of surveyed houses. (B) Reported number of Chagas disease cases in Moreno Department during 1988–1993 (mean) and 1994–2004.

Figure 2. Effects of the frequency of residual insecticide spraying of individual rural communities during 1993–2000 on the prevalence of domestic infestation by T. infestans observed in 2000 in Moreno Department.

Bold lines represent the median, boxes the first and third quartiles, and vertical lines the range.

Figure 3. Annual direct costs (in 2004 US$) of the implementation of a fully horizontal (observed data), vertical or mixed (estimated data) vector control strategy in rural communities of Moreno Department.

Figure 4. Sensitivity analysis of the different parameters used to estimate the direct cost-effectiveness of each vector control strategy in Moreno Department.

Lambda refers to disease incidence (cases per year); acute infection rate to the percentage of total cases represented by notified acute cases, and per diem represents a 50% reduction or the complete elimination of per diems. * indicates the baseline direct CE values. Mixed WT represents a mixed strategy that successfully interrupted disease transmission, whereas mixed WoT a mixed strategy that did not interrupted disease transmission.

Figure 5. Cumulative projection of the direct cost-effectiveness ratio (expressed in US$ per averted case) for each vector control strategy.

Mixed WT represents a mixed strategy that successfully interrupted disease transmission, whereas mixed WoT a mixed strategy that did not interrupted disease transmission.