Use of a Catalytic Model to Estimate Hepatitis A Incidence in a Low-Endemicity Country

Background. Evaluating the cost-effectiveness of vaccine programs with dynamic modeling requires accurate estimates of incidence over time. Because infectious diseases are often underreported, supplementary data and statistical analyses are required to estimate true incidence. This study estimates the true incidence of hepatitis A virus (HAV) infection in Canada using a catalytic model. Methods. A catalytic model was used to reconcile HAV seroprevalence data with the corresponding true cumulative risk of infection estimated from incidence data. Results. The average annual reported incidence was 6.2 cases per 100 000 from 1980 to 1989 and 7.7/100 000 from 1990 to 1999, indicating that Canada is a low-incidence country. The seroprevalence in Canadian-born individuals (n = 7 studies) was approximately 1%−8% in ages <20, 1%−11% in ages 20–29, 7%−29% in ages 30–39, and higher in older age groups. Between 1980 and 1995, the catalytic model estimated an average annual incidence of 60/100 000 (95% confidence interval, 33–524); approximately 7.73 (4.21–67.33) times the average annual reported incidence of 7.78/100 000. For a typical birth cohort of 403 434 Canadians born in 1990, the model predicted 32 750 HAV cases by age 39, with a corresponding seroprevalence of approximately 8.12% by the year 2029. Implications. Reliable estimates of true incidence of infectious disease are required for cost-effectiveness analysis of infectious disease programs. Catalytic models enable the synthesis of dispersed data, quantification of data limitations, and reconciliation of these limitations to estimate true incidence for economic evaluations.