Time to loss of physical integrity of attractive targeted sugar bait (ATSB) stations in Western Province, Zambia: a survival analysis.

BACKGROUND

Attractive targeted sugar baits (ATSBs) are a potential addition to an integrated vector management strategy against malaria. ATSB stations, which include a sugar bait and an ingestion toxicant, could potentially be deployed to attract-and-kill mosquitoes and thereby prevent malaria transmission. The physical durability of these stations is likely to be an important factor in decisions around future use strategies. This study measured the duration of physical integrity of the ATSB Sarabi v1.2 stations used in Western Zambia, as part of a Phase III cluster RCT.

METHODS

ATSB stations were installed and followed as a cohort on the external walls of selected sleeping structures in households in trial clusters (10-11 per cluster). Monthly visits were made to assess the presence and condition of the ATSBs from November 2022 to June 2023. A rolling cohort approach was used, whereby new ATSB stations were used to replace those which failed or were lost-to-follow-up, and these were subsequently enrolled in the cohort. Information on structure construction and ATSBs location on the walls was also collected. Median ATSB survival and associated factors were analysed with Kaplan-Meier curves and Cox-Proportional hazard models.

RESULTS

Including replacements, a total of 1107 ATSBs were installed across 304 sleeping structures in 206 households, and 5696 ATSB-visits were made. Common types of damage observed were holes/tears, mold, and leakage of bait. While the median survival time for the devices was 5 months (149 days) for all stations in the study, the median survival time was longer than the transmission season for stations installed in locations well protected by the roof (> 218 days). ATSB station survival was longer when installed on structures with thatched roofs compared to iron-sheet roofs (HR 0.37, 95% CI 0.26-0.47, p < 0.001), and where there was "excellent protection" (HR = 0.36, 95% CI 0.25-0.49, p < 0.001), compared to "no protection".

CONCLUSIONS

Study results suggest that the majority of ATSB stations deployed in this setting will remain intact for a 7-month seasonal deployment period if stations are installed in locations protected from weather elements, such as underneath the overhang of thatched roof. Further research is needed to understand factors that influence the physical integrity and efficacy of ATSB stations in addition to those observed in this study.