Article
Effects of urbanicity on malaria and the development of immunity – results from a hospital based study in Ghana
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Authors
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Clemens Frank
- Research Group Infectious Disease Epidemiology, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany
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Ralf Krumkamp
- Research Group Infectious Disease Epidemiology, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany
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Nimako Sarpong
- Kumasi Centre for Collaborative Research, Kumasi, Ghana
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Peter Sothmann
- Research Group Infectious Disease Epidemiology, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany
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Ellis Owusu-Dabo
- Kumasi Centre for Collaborative Research, Kumasi, Ghana
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Jürgen May
- Research Group Infectious Disease Epidemiology, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany
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Benno Kreuels
- Research Group Infectious Disease Epidemiology, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany; Section for Tropical Medicine, 1st Department of Internal Medicine, University Medical Centre Hamburg-Eppendorf, Germany
| Published: | January 29, 2014 |
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Outline
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Introduction: Malaria incidence has declined considerably over the last decade. This is partly due to a scale-up of control measures but may also be driven by a decline of vector populations due to urbanisation. The aim of this study was to analyse, on a micro-epidemiological scale, the association between malaria and urbanisation and a possible effect of urbanicity on the acquisition of immunity.
Methods: In 2012, children <15 years presenting to St. Michael’s Hospital in Pramso/Ghana with fever (≥38.0°C) were recruited. Malaria was defined as fever with a parasitaemia of ≥5000/µl. We used an innovative urbanicity-scale to measure the level of urbanicity of our study settlements to examine an association between urbanicity and malaria risk. The proportion of malaria cases to all fever cases („Malaria-Positive-Fraction of Fevers“ (MPF)) was calculated for each settlement as a proxy for malaria risk. To obtain stable estimates of the MPF villages with less than 20 participants were excluded. The median age of all malaria cases was calculated for each settlement as a proxy for how quickly immunity is acquired. Associations between MPF and urbanicity, MPF and median age, and urbanicity and median age were displayed using scatterplots with a regression line and corresponding 95% confidence interval and modelled using a linear regression.
Results: Of 2,567 recruited children, 2,274 (89%) from 28 settlements could be included in this analysis. There were 728 malaria cases (overall MPF 0.32). The MPF varied from 0.19 to 0.54 between settlements and was negatively associated with the level of urbanicity (coefficient: –4.5 per 10 points on the urbanicity-scale, R2: 0.63, p<0.001). Median age of children presenting with malaria varied from 31 to 64 months between settlements and was negatively associated with the MPF (coefficient: –3.7 per 0.1 MPF, R2: 0.19, p=0.03).
Discussion: Our results confirm an association between urbanisation and a declining prevalence of malaria. We also demonstrate that the acquisition of immunity is heterogeneous on a micro-epidemiological scale and that it is associated with transmission intensity.
