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Open Access Research article

Measuring underreporting and under-ascertainment in infectious disease datasets: a comparison of methods

Cheryl L Gibbons1*, Marie-Josée J Mangen2, Dietrich Plass3, Arie H Havelaar45, Russell John Brooke2, Piotr Kramarz6, Karen L Peterson1, Anke L Stuurman47, Alessandro Cassini6, Eric M Fèvre89, Mirjam EE Kretzschmar24 and On behalf of the Burden of Communicable diseases in Europe (BCoDE) consortium

Author Affiliations

1 Centre for Immunity, Infection and Evolution, Ashworth Laboratories, Kings Buildings, University of Edinburgh, Edinburgh, UK

2 Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, Utrecht, the Netherlands

3 Department of Public Health Medicine, School of Public Health, University of Bielefeld, Bielefeld, Germany

4 Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands

5 Institute for Risk Assessment Sciences, Utrecht University, Utrecht, the Netherlands

6 European Centre for Disease Prevention and Control, Stockholm, Sweden

7 Pallas, Health Research and Consultancy BV, Rotterdam, the Netherlands

8 International Livestock Research Institute, Nairobi, Kenya

9 Institute of Infection and Global Health, University of Liverpool, Liverpool, UK

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BMC Public Health 2014, 14:147  doi:10.1186/1471-2458-14-147

Published: 11 February 2014

Abstract

Background

Efficient and reliable surveillance and notification systems are vital for monitoring public health and disease outbreaks. However, most surveillance and notification systems are affected by a degree of underestimation (UE) and therefore uncertainty surrounds the 'true’ incidence of disease affecting morbidity and mortality rates. Surveillance systems fail to capture cases at two distinct levels of the surveillance pyramid: from the community since not all cases seek healthcare (under-ascertainment), and at the healthcare-level, representing a failure to adequately report symptomatic cases that have sought medical advice (underreporting). There are several methods to estimate the extent of under-ascertainment and underreporting.

Methods

Within the context of the ECDC-funded Burden of Communicable Diseases in Europe (BCoDE)-project, an extensive literature review was conducted to identify studies that estimate ascertainment or reporting rates for salmonellosis and campylobacteriosis in European Union Member States (MS) plus European Free Trade Area (EFTA) countries Iceland, Norway and Switzerland and four other OECD countries (USA, Canada, Australia and Japan). Multiplication factors (MFs), a measure of the magnitude of underestimation, were taken directly from the literature or derived (where the proportion of underestimated, under-ascertained, or underreported cases was known) and compared for the two pathogens.

Results

MFs varied between and within diseases and countries, representing a need to carefully select the most appropriate MFs and methods for calculating them. The most appropriate MFs are often disease-, country-, age-, and sex-specific.

Conclusions

When routine data are used to make decisions on resource allocation or to estimate epidemiological parameters in populations, it becomes important to understand when, where and to what extent these data represent the true picture of disease, and in some instances (such as priority setting) it is necessary to adjust for underestimation. MFs can be used to adjust notification and surveillance data to provide more realistic estimates of incidence.

Keywords:
Underestimation; Underreporting; Under-ascertainment; Surveillance; Infectious diseases