Wednesday, 6th of April 2011 |
Szusz and colleagues review existing datasets and look at those needed properly to model measles in developing countries.
'The classic threshold result describing the critical proportion immune (*p*c) required to eradicate an infectious disease, *p*c = 1-1/*R*0, may overestimate the required
proportion immune to eradicate measles in some developing country populations.’
Abstract is below; full text, at http://www.biomedcentral.com/1756-0500/3/75
Good reading.
BD
* *
A review of data needed to parameterize a dynamic model of measles in developing countries
Emily K Szusz*1, Louis P Garrison*2 and Chris T Bauch*1
1 Department of Mathematics and Statistics, University of Guelph, Guelph,
Canada
2 Department of Pharmacy, University of Washington, Seattle, Washington,
USA
*BMC Research Notes* 2010, *3:*75doi:10.1186/1756-0500-3-75
The electronic version of this article is the complete one and can be found
online at: http://www.biomedcentral.com/1756-0500/3/75
© 2010 Bauch et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0),
which permits unrestricted use, distribution, and reproduction in any
medium, provided the original work is properly cited.
Abstract
Background
Dynamic models of infection transmission can project future disease burden
within a population. Few dynamic measles models have been developed for
low-income countries, where measles disease burden is highest. Our objective
was to review the literature on measles epidemiology in low-income
countries, with a particular focus on data that are needed to parameterize
dynamic models.
Methods
We included age-stratified case reporting and seroprevalence studies with
fair to good sample sizes for mostly urban African and Indian populations.
We emphasized studies conducted before widespread immunization. We
summarized age-stratified attack rates and seroprevalence profiles across
these populations. Using the study data, we fitted a "representative"
seroprevalence profile for African and Indian settings. We also used a
catalytic model to estimate the age-dependent force of infection for
individual African and Indian studies where seroprevalence was surveyed. We
used these data to quantify the effects of population density on the basic
reproductive number *R*0.
Results
The peak attack rate usually occurred at age 1 year in Africa, and 1 to 2
years in India, which is earlier than in developed countries before mass
vaccination. Approximately 60% of children were seropositive for measles
antibody by age 2 in Africa and India, according to the representative
seroprevalence profiles. A statistically significant decline in the force of
infection with age was found in 4 of 6 Indian seroprevalence studies, but
not in 2 African studies. This implies that the classic threshold result
describing the critical proportion immune (*p*c) required to eradicate an
infectious disease, *p*c = 1-1/*R*0, may overestimate the required
proportion immune to eradicate measles in some developing country
populations. A possible, though not statistically significant, positive
relation between population density and *R*0 for various Indian and African
populations was also found. These populations also showed a similar pattern
of waning of maternal antibodies. Attack rates in rural Indian populations
show little dependence on vaccine coverage or population density compared to
urban Indian populations. Estimated *R*0 values varied widely across
populations which has further implications for measles elimination.
Conclusions
It is possible to develop a broadly informative dynamic model of measles transmission in low-income country settings based on existing literature, though it may be difficult to develop a model that is closely tailored to any given country. Greater efforts to collect data specific to low-income countries would aid in control efforts by allowing highly
population-specific models to be developed.
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