The Impact of Diarrhoea Measurement Methods for Under-Fives in Low and Middle Income Countries on Reported Diarrhoea Rates: A Systematic Review and Meta-Analysis of Methodological and Primary Empirical Studies

Background: Diarrhoea is the second highest cause of under-five death globally. Measurement of under-five diarrhoea rates is necessary to evaluate interventions. However, differences in findings across studies might reflect differences in measurement methods rather than true diarrhoea rates.  Methods: We systematically reviewed all studies published between 2000 and 2018 that reported under-five diarrhoea rates in low and middle income countries and extracted data on diarrhoea rates, measurement methods, and reactivity. 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 reported diarrhoea rates.  Findings: Two-hundred-and-seventy-seven studies met our inclusion criteria: four direct comparisons and 273 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 96% lower reported rate than active surveillance(IRR=0·04,95%CI[0·02,0·09]). Among active surveillance studies, a doubling of recall period was associated with a 47% lower rate(IRR=0·53[0·46,0·60]), while decreased questioning frequency was associated with a higher reported rate: at the extreme, one time questioning yielded a nearly 4X higher rate than daily questioning(IRR=3·84[2·48,5·96]).  Interpretation: Reported 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 gastro-intestinal health. Funding Statement: The project was funded by the National Institutes for Health Research Global Health Research Unit on Improving Health in Slums(16/136/87) using UK aid from the UK Government. Declaration of Interests: The authors declare no conflict of interests.