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The validation of a three-stage screening methodology for detecting active convulsive epilepsy in population-based studies in health and demographic surveillance systems

Anthony K Ngugi123*, Christian Bottomley24, Eddie Chengo1, Martha Z Kombe1, Michael Kazungu1, Evasius Bauni15, Caroline K Mbuba1, Immo Kleinschmidt24 and Charles R Newton13678

Author Affiliations

1 The Centre for Geographic Medicine Research – Coast, KEMRI/Wellcome Trust Research Programme, Kilifi, Kenya

2 Department of Infectious Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK

3 Studies of Epidemiology of Epilepsy in Demographic Surveillance Systems (SEEDS) – INDEPTH Network, Accra, Ghana

4 MRC Tropical Epidemiology Group, Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK

5 INDEPTH Network, Accra, Ghana

6 Clinical Research Unit, London School of Hygiene and Tropical Medicine, London, UK

7 Neurosciences Unit, UCL Institute of Child Health, London, UK

8 Department of Psychiatry, University of Oxford, Oxford, UK

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Emerging Themes in Epidemiology 2012, 9:8  doi:10.1186/1742-7622-9-8

Published: 21 November 2012

Abstract

Background

There are few studies on the epidemiology of epilepsy in large populations in Low and Middle Income Countries (LMIC). Most studies in these regions use two-stage population-based screening surveys, which are time-consuming and costly to implement in large populations required to generate accurate estimates. We examined the sensitivity and specificity of a three-stage cross-sectional screening methodology in detecting active convulsive epilepsy (ACE), which can be embedded within on-going census of demographic surveillance systems.

We validated a three-stage cross-sectional screening methodology on a randomly selected sample of participants of a three-stage prevalence survey of epilepsy. Diagnosis of ACE by an experienced clinician was used as ‘gold standard’. We further compared the expenditure of this method with the standard two-stage methodology.

Results

We screened 4442 subjects in the validation and identified 35 cases of ACE. Of these, 18 were identified as false negatives, most of whom (15/18) were missed in the first stage and a few (3/18) in the second stage of the three-stage screening. Overall, this methodology had a sensitivity of 48.6% and a specificity of 100%. It was 37% cheaper than a two-stage survey.

Conclusion

This was the first study to evaluate the performance of a multi-stage screening methodology used to detect epilepsy in demographic surveillance sites. This method had poor sensitivity attributed mainly to stigma-related non-response in the first stage. This method needs to take into consideration the poor sensitivity and the savings in expenditure and time as well as validation in target populations. Our findings suggest the need for continued efforts to develop and improve case-ascertainment methods in population-based epidemiological studies of epilepsy in LMIC.

Keywords:
Epilepsy; Three-stage methodology; Screening; Validation; Sensitivity; LMIC