ORIGINAL ARTICLE Burden of rotavirus hospitalisations in young children in three paediatric hospitals in the United States determined by active surveillance compared to standard indirect methods David O Matson, 1 Mary Allen Staat, 4 Parvin Azimi, 5 Robbin Itzler, 6 David I Bernstein, 4 Richard L Ward, 4 Ram Dahiya, 2 Mark J DiNubile, 6 Myra Barnes-Eley 3 and Tamas Berke 3 * 1 Graduate Program in Public Health, Eastern Virginia Medical School and Old Dominion University, 2 Department of Medicine, Old Dominion University, 3 Center for Pediatric Research, Eastern Virginia Medical School, Norfolk, Virginia, 4 Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, 5 Children’s Hospital of Oakland, Oakland, California and 6 Merck Research Laboratories, North Wales, Pennsylvania, United States Aim: The number of rotavirus hospitalisations is usually estimated from assigned diagnosis codes for gastroenteritis despite lack of validation for these indirect methods. Reliable estimates before and after introduction of vaccines are needed to quantify the absolute impact of new immunisation programs. Methods: This 2-year study conducted at three hospitals prior to the licensure of the rotavirus vaccines in the USA compared two indirect methods for estimating hospitalisations for rotavirus gastroenteritis with estimates derived from prospective recruitment of children presenting with diarrhoea, vomiting or fever. For active surveillance, rotavirus gastroenteritis was confirmed by demonstration of stool antigen. The indirect residual and proportional methods assumed rotavirus to have caused a proportion of hospitalisations coded as acute gastroenteritis identified from computerised records. Results: There were 447 rotavirus hospitalisations among inpatients 31 days through 4 years of age admitted with vomiting and/or diarrhoea, compared with 306 and 228 hospitalisations identified by the two indirect methods. Only 52% of children hospitalised with gastroenteritis received a qualifying diagnosis code at discharge. Relative to active surveillance, the sensitivity and specificity (95% confidence interval (CI)) in identifying rotavirus-attributable hospitalisations was 45% (95% CI: 43–48%) and 89% (88–90%) for the residual method and 34% (30–39%) and 92% (90–94%) for the proportional method. Conclusions: Many children admitted to the hospital with diarrhoea, vomiting or fever were not assigned discharge codes for acute gastro- enteritis. Consequently, standard indirect methods missed a substantial number of rotavirus-associated hospitalisations, thereby underestimat- ing the absolute number of children who could potentially benefit from vaccination. Key words: active surveillance; diagnostic code; gastroenteritis; hospitalisation; rotavirus. What is already known on this topic 1 Safe and efficacious rotavirus vaccines have been shown to diminish health-care utilisation associated with rotavirus gastroenteritis. 2 Reliable estimates of the incidence of rotavirus infections neces- sitating hospitalisation before and after introduction of vaccines are needed to quantify the absolute impact of new immunisa- tion programs. 3 The number of rotavirus hospitalisations is usually estimated from assigned diagnosis codes for gastroenteritis despite lack of validation for these indirect methods. What this paper adds 1 Many children admitted to the hospital with diarrhoea, vomiting and/or fever were not assigned discharge codes for acute gastroenteritis. 2 Indirect methods missed a substantial number of rotavirus- associated hospitalisations, thereby underestimating the poten- tial impact of vaccination. 3 Conscientious use of appropriate diagnosis codes could improve estimates derived from indirect methods. Correspondence: Dr David Matson, Graduate Program in Public Health, Eastern Virginia Medical School and Old Dominion University, PO Box 1980, Norfolk, VA 23501, USA. Fax: +757 446 6121; email: matsondo@emvs.edu *Present affiliation: Department of Preclinical Research and Development; Intercell AG; Campus Vienna Biocenter 6; 1030 Vienna, Austria. Potential Conflicts of Interest: All academic authors are or have been investigators and/or consultants for Merck. DOM has been a consultant and speaker for Merck and GlaxoSmithKline (which both market rotavirus vaccines) and has received grant support from Merck and Wyeth. RI and MJD are employees of Merck, and own stock and stock options in the company. This work was supported by United States Public Health Service grant (contract N01 AI 452252) and unrestricted grants from Wyeth-Lederle and Merck. Accepted for publication 9 September 2011. doi:10.1111/j.1440-1754.2012.02445.x Journal of Paediatrics and Child Health 48 (2012) 698–704 © 2012 The Authors Journal of Paediatrics and Child Health © 2012 Paediatrics and Child Health Division (Royal Australasian College of Physicians) 698