Laboratory development and field testing of sentinel toys to assess environmental faecal exposure of young children in rural India

Background: Sentinel toys are increasingly used as a method of assessing young children's exposure to faecal pathogens in households in low-income settings. However, there is no consensus on the suitability of different approaches. Methods: We evaluated three types of toy balls with different surfaces (plastic, rubber, urethane) in the laboratory to compare the uptake of faecal indicator bacteria (Escherichia coli) on their surface. We performed bacteria survival analysis under different environmental conditions and tested laboratory methods for bacteria removal and recovery. In a field study we distributed sterile urethane balls to children,5 from 360 households in rural India. After 24 hours, we collected and rinsed the toys in sterile water, assayed for thermotolerant coliforms (TTC) and explored associations between the level of contamination and household characteristics. Results: In the laboratory, urethane foam balls took up more indicator bacteria than the other balls. Bacteria recovery did not differ based on mechanic vs no agitation. Higher temperatures and moisture levels increased bacterial yield. In the field, the only factor associated with a decreased recovery of TTC from the balls was having a soil (unpaved) floor. Conclusions: Sentinel toys may be an effective tool for assessing young children's exposure to faecal pathogens. However, even using methods designed to increase bacterial recovery, limited sensitivity may require larger sample sizes.