Acute intussusception in infants and children as an adverse event following immunization: case definition and guidelines of data collection, analysis, and presentation

[...]a range of atypical symptoms is reported to occur with intussusception. Because of the range of atypical symptoms reported to be associated with intussusception, no clinical case definition can be expected to identify all patients presenting with this condition. Data should be presented with numerator and denominator (n/N) and not in percentages only. Since in surveillance systems denominator data are usually not readily available, attempts should be made to identify approximate denominators.