Academic journal article Bulletin of the World Health Organization

Estimating the Number of Helminthic Infections in the Republic of Cameroon from Data on Infection Prevalence in Schoolchildren

Academic journal article Bulletin of the World Health Organization

Estimating the Number of Helminthic Infections in the Republic of Cameroon from Data on Infection Prevalence in Schoolchildren

Article excerpt

Bulletin of the World Health Organization, 2000, 79: 1456-1465.

Voir page 1463 le resume en francais. En la pagina 1464 figura un resumen en espanol.

Introduction

When planning interventions to control a disease, it is essential to understand the burden of the disease. In the absence of reliable data on the total number of helminthic infections in a country, estimates have often been based on prevalence data from a few limited studies which have then been extrapolated to the country as a whole (1-5). Although these estimates may provide an indication of the scale of the problem, they do not provide data on the age distribution of the infection. Yet because of the marked association between age and prevalence in many diseases (Fig. 1) information on patterns of distribution by age is essential in planning control measures within countries and for quantifying the burden of disease (5). One reason that age distribution has not been incorporated in previous estimates is because most data on prevalence have come primarily from school-aged children (6).

[Figure 1 ILLUSTRATION OMITTED]

We investigated the relation between the prevalence of helminthic infection in the community and the prevalence among schoolchildren in studies across Africa (7) and showed that at all levels of infection prevalence in schoolchildren is typically higher than prevalence in the entire community, with the absolute difference depending on the species. These observations suggest that if used in isolation prevalence data from schoolchildren will tend to produce an overestimate of the number of people infected when compared with estimates based on prevalence data for the community. However, prevalence among the whole community can be predicted from models that are species specific.

The geographical distribution of infection is also important in providing reliable estimates of the number of people infected. Current procedures either ignore spatial distribution or assume a normal distribution (4, 8-10). In practice there are few studies that have explored this issue, despite spatial heterogeneity in prevalence having the potential to introduce further bias into any estimate.

This paper builds on recent work (7) and provides a practical means for extrapolating from prevalence data on school-aged children to the prevalence of infection in the total community and thus the total number infected for each of the major species of helminth. This approach uses the example of the Republic of Cameroon because nationwide survey data exist (11-13), and investigates the differences in estimates of the total number of infections based on prevalence data for school-aged children alone or extrapolated to the whole community. Because of the inherent potential for error in the use of any extrapolation procedure, this paper also assesses the reliability of model-based estimates to shed light on whether further investigations into these relations is required. Finally, investigations are carried out to explore how estimates alter in relation to spatial scale by aggregating infection data for three geographical levels (district, regional, and national).

Methods

Overview

Using data on the prevalence of helminthic infection in schoolchildren in Cameroon, the prevalence of infection in pre-school children and adults was estimated from species-specific logistic regression models and linear regression models that were developed earlier (7). Estimates and confidence intervals are provided in order to assess the reliability of the predictions. Both the best-fit logistic regression models and the linear regression models are used to estimate the prevalence of infection, to examine the differences arising from the two approaches and to determine whether a single, consistent approach could be used. The predictions from the linear regression model are then used to estimate the number of people infected in each district in other age groups (preschool and adult populations); these are then summed to estimate the total number of people in the country who are infected. …

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