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 4× 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.