Rapid, Active Surveillance for Medically Attended Acute Gastroenteritis and Norovirus Infection in a Managed Care Environment

Background/Aims: Norovirus is the leading cause of acute gastroenteritis in the United States and is the leading cause of medically attended acute gastroenteritis (MAAGE) among children younger than five years of age. Our primary goal is to describe the community incidence of MAAGE and the proportion of MAAGE encounters due to norovirus within the membership population of Kaiser Permanente Northwest (KPNW). Our secondary goal is to describe transmission of norovirus within households. Methods: We are conducting a 12-month active surveillance project in which we identify all KPNW members with MAAGE-associated health care encounters through daily electronic abstraction of the electronic health record system. We are recruiting a sample of this population daily, along with their symptomatic household members, to complete a recruitment survey and collect a stool sample for norovirus testing. Results: During the four months of our surveillance period, we identified 6,156 members presenting for MAAGE (annualized incidence of 413/100,000). We attempted to reach 1,782 (30%) potential participants, 525 (29%) of whom were ineligible. Of those remaining, 708 (56%) refused and 549 (44%) agreed to participate. Of those agreeing to participate, 453 (83%) provided a sample from which we obtained viral testing results. Among samples tested, we identified 52 (11%) positive for norovirus. Norovirus positivity was highest among those 0–4 years of age (20%) and lowest among those 65 years or older (6%). Thus far, we have recruited 48 household members, 8 (15%) of whom tested positive for norovirus; 7 (88%) had the same laboratory results as their MAAGE-associated household member. Discussion: Our observed incidence of MAAGE and proportion of MAAGE encounters due to norovirus infection in the KPNW member population over the first four months of our surveillance period are consistent with results obtained from other studies using varying methodologies and reinforce the high burden of MAAGE and norovirus infection within the community. Our results further support the high transmission of norovirus infection within households. Importantly, our project –– with 44% agreeing to participate and 83% collecting and returning a stool sample –– demonstrates a model for conducting other community-based studies of acute infectious diseases within a managed care system