Two diarrhoea severity scales, the 20-point Vesikari scale and the 24-point Clark scale, are commonly used to assess the efficacy of rotavirus vaccines. However, the two scales have been compared previously in only a few studies by using the same patients.

The study was aimed to compare the Clark and Vesikari scales and to determine whether modified classifications would provide a better correlation between the two scales.

A total of 200 children with rotavirus gastroenteritis (RVGE) were evaluated. Of these, 57% were classified as severe by the Vesikari scale, while only 1.5% by the Clark scale (p < 0.001). When the Clark 3-category scale was transformed into 2-category scale by merging mild and moderate categories as non-severe, a good correlation with the Vesikari scale could not be found. Using the median of the severity scores as the severity threshold, could not provide a better correlation between the two scales either. Transforming the Vesikari 2-category scale into a 3-category scale by further subdividing the severe category into two parts as moderate and severe (≥16), thus using a score of 16 point as the severity threshold, provided a better correlation between the two severity scales, but still did not achieve a good level of agreement. Furthermore, still 89% of all those with Vesikari score ≥16 were classified as mild or moderate by the Clark scale.

The Clark and Vesikari severity scales differ significantly in the definition of severe RVGE. Even the reclassification attempts on the scales did not achieve a good correlation between the two scales.