A review of changing episode definitions and their effects on estimates of diarrhoeal morbidity.

This paper describes how the methodology used for measuring diarrhoeal morbidity has changed over time and assesses how differences in episode definition have affected estimates of diarrhoeal morbidity among children aged less than five years. The episode definition used in 73 studies included in three previously-published literature reviews was identified. In earlier work, a method was developed that adjusts morbidity estimates to take account of differences in episode definition. This adjustment method was applied to the studies identified in these three literature reviews. Episode definitions were better documented and were more consistent in studies published after 1980. Adjusting morbidity estimates to account for definitional differences did not substantially alter the reviews' conclusions. Diarrhoeal surveillance has steadily improved since 1980, with methodology becoming more consistent between studies and better documented. Although episode definitions have changed over time, the morbidity estimates derived in the three reviews appear robust to these changes.

Defining episodes of diarrhoea: results from a three-country study in Sub-Saharan Africa.

The study was conducted to assess the effect of definition of episode on diarrhoeal morbidity and to develop a means of adjusting estimates of morbidity for the definition of episode used. This paper reports on a cohort study of 374 children, aged 9-32 months, in three African countries, which recorded frequency and consistency of stool over a seven-month period. Different definitions of episode were applied to these data to assess their effect on annualized diarrhoeal morbidity. Adjustment factors were then derived that corrected morbidity for non-standard definitions of episode. Applying non-standard definitions of episode gave estimates of an annualized number of episodes between 38% and 137% of the internationally-accepted definition. Researchers should be encouraged to use the standard definition of episode of diarrhoea and to use appropriate field protocols. Where this is not possible, correction factors should be applied, particularly where estimates of diarrhoeal morbidity are pooled in systematic reviews.