The impact of diarrhoea measurement methods for under 5s in low- and middle-income countries on estimated diarrhoea rates at the population level: A systematic review and meta-analysis of methodological and primary empirical studies

Objective We systematically reviewed all studies published between 2000 and June 2021 that estimated under 5 diarrhoea rates in low- and middle-income countries and extracted data on diarrhoea rates, measurement methods and reactivity. Methods We summarised data from studies that performed direct comparisons of methods, and indirectly compared studies which utilised only one method using meta-regression to determine the association between methods and estimated diarrhoea rates. Results In total, 288 studies met our inclusion criteria: 4 direct comparisons and 284 studies utilising only one measurement method. Meta-regression across all studies showed that diarrhoea rates were sensitive to method of measurement. We estimated that passive surveillance methods were associated with a 97% lower estimated rate than active surveillance (IRR = 0.03, 95% CI [0.02, 0.06]). Among active surveillance studies, a doubling of recall period was associated with a 48% lower rate (IRR = 0.52 [0.46, 0.60]), while decreased questioning frequency was associated with a higher estimated rate: at the extreme, one time questioning yielded an over 4x higher rate than daily questioning (IRR = 4.22 [2.73, 6.52]). Conclusions Estimated diarrhoea rates are sensitive to their measurement methods. There is a need for a standardisation of diarrhoea measurement methods, and for the use of other outcomes in the measurement of population-level gastrointestinal health.