Prevalence and incidence of epilepsy in a well-defined population of Northern Italy

Abstract

Objective: To calculate prevalence and incidence of epilepsy using administrative records.

Methods: Claim records from the administrative district of Lecco, Northern Italy (population 311,637; 2001 census), collected during the years 2000-2008, were the data source. Patients of all ages were included. Based on previous findings from our group, the most accurate algorithm to detect epilepsy was the combination of electroencephalography (EEG) (ad hoc code) (at least one during the study period) and antiepileptic drugs (AEDs) (ATC code) (taken in 2008). Using this algorithm, the prevalence of epilepsy for the year 2008 was calculated. The reference population for prevalence was the population residing in the study area during the year 2008. Incident epilepsy cases were a subset of prevalent cases among patients not traced in the years 2000 through 2003. Average annual incidence rates were calculated for 2004 through 2008, taking for reference the person-years of exposure in the resident population. We calculated crude, adjusted (using positive and negative predictive values), and standardized (to the Italian and World population) prevalence and incidence.

Results: In 2008, 1,504 patients met the inclusion criteria, giving a prevalence of 4.57 per 1,000 (women 4.26; men 4.89). Prevalence tended to rise slightly with age. There were 864 incident cases, giving an average annual incidence of 53.41 per 100,000 (women 50.98; men 55.95). Incidence rates peaked in the elderly. The adjusted prevalence was 4.42 and the adjusted incidence 47.05. Standardized prevalence and incidence were, respectively, 4.30 per 1,000 and 48.35 per 100,000 (Italian population) and 3.79 per 1,000 and 44.74 per 100,000 (World population).

Significance: The prevalence of epilepsy in the Lecco district was comparable to other studies, whereas the incidence was among the highest. With adjustments, administrative records are a cost-effective instrument to monitor epilepsy frequency.

Keywords: Administrative data; Epilepsy; Incidence; Prevalence; Validity.