Indirect protection and indirect measures of protection from rotavirus in adults.

TO THE EDITOR—We read with interest the recent article by Lopman et al [1], who used International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9CM) data from the Nationwide Inpatient Sample (NIS) to document a decline in rotavirus and cause-unspecified gastroenteritis in 2008 in patients <24 years of age following widespread implementation of pediatric rotavirus vaccination. Despite the fact that administrative coding (ICD-9CM) data have been widely used [1–6], we are unaware of data regarding how well these codes identify hospitalized adults with all-cause gastroenteritis. In addition, important differences exist in the ICD-9CM codes used in studies, depending on whether the focus was on foodborne illness or all-cause gastroenteritis. Analysis of administrative data that was performed for rotavirus in children showed an underestimation of rotavirus in that population [7]. As part of an institutional review board–approved study of the prevalence of rotavirus among adults hospitalized at Northwestern Memorial Hospital (Chicago, Illinois) from 1 December 2005 through 30 November 2006, who had a stool specimen submitted for bacterial stool culture (BSC) [8], we compared how well ICD9CM codes were able to identify patients with gastroenteritis when compared with having a BSC obtained, a surrogate for a clinical diagnosis of gastroenteritis. We used the criteria from the sentinel study of Mounts et al [3]. Any patient with an ICD-9CM code of 008.45 (Clostridium difficile) was reviewed and Table 1. Comparison Between Patients With an ICD-9CM Code Consistent With Gastroenteritis and Those Who Have a Bacterial Stool Culture Saved