a1 Epidemiology Services, British Columbia Centre for Disease Control, Vancouver, BC, Canada
a2 Foodborne, Waterborne, and Zoonotic Infections Division, Public Health Agency of Canada, Guelph, Ontario, Canada
a3 Department of Population Medicine, University of Guelph, Guelph, Ontario, Canada
Under-reporting of infectious gastrointestinal illness (IGI) in British Columbia, Canada was calculated using simulation modelling, accounting for the uncertainty and variability of input parameters. Factors affecting under-reporting were assessed during a cross-sectional randomized telephone survey. For every case of IGI reported to the province, a mean of 347 community cases occurred (5th and 95th percentile estimates ranged from 181 to 611 community cases, respectively). Vomiting [odds ratio (OR) 2·15, 95% confidence interval (CI) 1·03–4·49] and antibiotic use in the previous 28 days (OR 3·59, 95% CI 1·17–10·97) significantly predicted health-care visits in a logistic regression model. In bivariate analyses, physicians were significantly less likely to request stool samples from patients with vomiting (RR 0·09, 95% CI 0·01–0·65) and patients of North American as opposed to non-North American cultural groups (RR 0·38, 95% CI 0·15–0·96). Physicians were more likely to request stool samples from older patients (P=0·003), patients with fewer household members (P=0·002) and those who reported anti-diarrhoeal use following illness (RR 3·33, 95% CI 1·32–8·45). People with symptoms of vomiting were under-represented in provincial communicable disease statistics. Differential degrees of under-reporting must be understood before biased surveillance data can be adjusted.
(Accepted March 09 2007)
(Online publication April 16 2007)
c1 Author for correspondence: Ms. L. MacDougall, Surveillance Epidemiologist, British Columbia Centre for Disease Control, 655 W12th Avenue, Vancouver, BC, V5Z 4R4, Canada. (Email: Laura.MacDougall@bccdc.ca)