Representativeness of a mobile phone-based coverage evaluation survey following mass drug administration for soil-transmitted helminths: a comparison of participation between two cross-sectional surveys

Objectives With increasing mobile phone subscriptions, phone-based surveys are gaining popularity with public health programmes. Despite advantages, systematic exclusion of participants may limit representativeness. Similar to control programmes for neglected tropical diseases (NTDs), the DeWorm3 trial of biannual community-wide mass drug administration (MDA) for elimination of soil-transmitted helminth infection used in-person coverage evaluation surveys to measure the proportion of the at-risk population treated during MDA. Due to lockdown during the COVID-19 pandemic, a phone-based coverage evaluation survey was necessary, providing an opportunity for the current study to compare representativeness and implementation (including non-response) of these two survey modes. Design Comparison of two cross-sectional surveys. Setting The DeWorm3 trial site in Tamil Nadu, India, includes Timiri, a rural subsite, and Jawadhu Hills, a hilly, hard-to-reach subsite inhabited predominantly by a tribal population. Participants In the phone-based and in-person coverage evaluation surveys, all individuals residing in 2000 randomly selected households (50 in each of the 40 trial clusters) were eligible to participate. Here, we characterise household participation. Results Of 2000 households, 1780 (89.0%) participated during the in-person survey. Of 2000 households selected for the phone survey, 346 (17.3%) could not be contacted as they had not provided a telephone number during the census and 1144 (57.2%) participated. Smaller households, households with lower socioeconomic status and those with older, women or less educated household-heads were under-represented in the phone-based survey compared with censused households. Regression analysis revealed non-response in the phone-based survey was higher among households from the poorest socioeconomic quintile (prevalence ratio (PR) 2.3, 95% CI 2.0 to 2.7) and lower when heads of households had completed secondary school or higher education (PR 0.7, 95% CI 0.6 to 0.8). Conclusions Our findings suggest phone-based surveys under-represent households likely to be at higher risk of NTDs and in-person surveys are more appropriate for measuring MDA coverage within programmatic settings.