Giuseppe
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[Source: PLoS Med., full text: (LINK). Abstract, edited.]
A Statistical Model of the International Spread of Wild Poliovirus in Africa Used to Predict and Prevent Outbreaks
Kathleen M. O'Reilly<SUP>1</SUP><SUP>*</SUP>, Claire Chauvin<SUP>2</SUP>, R. Bruce Aylward<SUP>2</SUP>, Chris Maher<SUP>2</SUP>, Sam Okiror<SUP>3</SUP>, Chris Wolff<SUP>2</SUP>, Deo Nshmirimana<SUP>3</SUP>, Christl A. Donnelly<SUP>1</SUP>, Nicholas C. Grassly<SUP>1</SUP>
1 Medical Research Council Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, United Kingdom, 2 Global Polio Eradication Initiative, World Health Organization, Geneva, Switzerland, 3 Immunizations and Vaccine Development, World Health Organization, Brazzaville, Republic of the Congo
Abstract
Background
Outbreaks of poliomyelitis in African countries that were previously free of wild-type poliovirus cost the Global Polio Eradication Initiative US$850 million during 2003?2009, and have limited the ability of the program to focus on endemic countries. A quantitative understanding of the factors that predict the distribution and timing of outbreaks will enable their prevention and facilitate the completion of global eradication.
Methods and Findings
Children with poliomyelitis in Africa from 1 January 2003 to 31 December 2010 were identified through routine surveillance of cases of acute flaccid paralysis, and separate outbreaks associated with importation of wild-type poliovirus were defined using the genetic relatedness of these viruses in the VP1/2A region. Potential explanatory variables were examined for their association with the number, size, and duration of poliomyelitis outbreaks in 6-mo periods using multivariable regression analysis. The predictive ability of 6-mo-ahead forecasts of poliomyelitis outbreaks in each country based on the regression model was assessed. A total of 142 genetically distinct outbreaks of poliomyelitis were recorded in 25 African countries, resulting in 1?228 cases (median of two cases). The estimated number of people arriving from infected countries and <5-y childhood mortality were independently associated with the number of outbreaks. Immunisation coverage based on the reported vaccination history of children with non-polio acute flaccid paralysis was associated with the duration and size of each outbreak, as well as the number of outbreaks. Six-month-ahead forecasts of the number of outbreaks in a country or region changed over time and had a predictive ability of 82%.
Conclusions
Outbreaks of poliomyelitis resulted primarily from continued transmission in Nigeria and the poor immunisation status of populations in neighbouring countries. From 1 January 2010 to 30 June 2011, reduced transmission in Nigeria and increased incidence in reinfected countries in west and central Africa have changed the geographical risk of polio outbreaks, and will require careful immunisation planning to limit onward spread.
Please see later in the article for the Editors' Summary
Citation: O'Reilly KM, Chauvin C, Aylward RB, Maher C, Okiror S, et al. (2011) A Statistical Model of the International Spread of Wild Poliovirus in Africa Used to Predict and Prevent Outbreaks. PLoS Med 8(10): e1001109. doi:10.1371/journal.pmed.1001109
Academic Editor: Mirjam Kretzschmar, The National Institute for Public Health and the Environment, Netherlands
Received: October 6, 2010; Accepted: September 7, 2011; Published: October 18, 2011
Copyright: ? 2011 O'Reilly et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was funded by the Poliovirus Research subcommittee of the WHO, a Royal Society University Research Fellowship to NCG. KMO, NCG, and CAD acknowledge the Medical Research Council for funding of the MRC Centre for Outbreak Analysis and Modelling at Imperial College. WHO is one of the spearheading partners of GPEI, and provides technical assistance and supports surveillance for acute flaccid paralysis. The Royal Society and the Medical Research Council had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: CM is a serving staff member of the World Health Organization. NG has received funding from the World Health Organization. All other authors have declared that no competing interests exist.
Abbreviations: AIC, Akaike's information criteria; AFP, acute flaccid paralysis; AUC, area under the curve; CI, confidence interval; DRC, the Democratic Republic of the Congo; GPEI, Global Polio Eradication Initiative; OPV, oral poliovirus vaccine; SE, standard error; SIA, supplementary immunisation activity; WHO, World Health Organization
* E-mail: k.oreilly@imperial.ac.uk
- -------Kathleen M. O'Reilly<SUP>1</SUP><SUP>*</SUP>, Claire Chauvin<SUP>2</SUP>, R. Bruce Aylward<SUP>2</SUP>, Chris Maher<SUP>2</SUP>, Sam Okiror<SUP>3</SUP>, Chris Wolff<SUP>2</SUP>, Deo Nshmirimana<SUP>3</SUP>, Christl A. Donnelly<SUP>1</SUP>, Nicholas C. Grassly<SUP>1</SUP>
1 Medical Research Council Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, United Kingdom, 2 Global Polio Eradication Initiative, World Health Organization, Geneva, Switzerland, 3 Immunizations and Vaccine Development, World Health Organization, Brazzaville, Republic of the Congo
Abstract
Background
Outbreaks of poliomyelitis in African countries that were previously free of wild-type poliovirus cost the Global Polio Eradication Initiative US$850 million during 2003?2009, and have limited the ability of the program to focus on endemic countries. A quantitative understanding of the factors that predict the distribution and timing of outbreaks will enable their prevention and facilitate the completion of global eradication.
Methods and Findings
Children with poliomyelitis in Africa from 1 January 2003 to 31 December 2010 were identified through routine surveillance of cases of acute flaccid paralysis, and separate outbreaks associated with importation of wild-type poliovirus were defined using the genetic relatedness of these viruses in the VP1/2A region. Potential explanatory variables were examined for their association with the number, size, and duration of poliomyelitis outbreaks in 6-mo periods using multivariable regression analysis. The predictive ability of 6-mo-ahead forecasts of poliomyelitis outbreaks in each country based on the regression model was assessed. A total of 142 genetically distinct outbreaks of poliomyelitis were recorded in 25 African countries, resulting in 1?228 cases (median of two cases). The estimated number of people arriving from infected countries and <5-y childhood mortality were independently associated with the number of outbreaks. Immunisation coverage based on the reported vaccination history of children with non-polio acute flaccid paralysis was associated with the duration and size of each outbreak, as well as the number of outbreaks. Six-month-ahead forecasts of the number of outbreaks in a country or region changed over time and had a predictive ability of 82%.
Conclusions
Outbreaks of poliomyelitis resulted primarily from continued transmission in Nigeria and the poor immunisation status of populations in neighbouring countries. From 1 January 2010 to 30 June 2011, reduced transmission in Nigeria and increased incidence in reinfected countries in west and central Africa have changed the geographical risk of polio outbreaks, and will require careful immunisation planning to limit onward spread.
Please see later in the article for the Editors' Summary
Citation: O'Reilly KM, Chauvin C, Aylward RB, Maher C, Okiror S, et al. (2011) A Statistical Model of the International Spread of Wild Poliovirus in Africa Used to Predict and Prevent Outbreaks. PLoS Med 8(10): e1001109. doi:10.1371/journal.pmed.1001109
Academic Editor: Mirjam Kretzschmar, The National Institute for Public Health and the Environment, Netherlands
Received: October 6, 2010; Accepted: September 7, 2011; Published: October 18, 2011
Copyright: ? 2011 O'Reilly et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was funded by the Poliovirus Research subcommittee of the WHO, a Royal Society University Research Fellowship to NCG. KMO, NCG, and CAD acknowledge the Medical Research Council for funding of the MRC Centre for Outbreak Analysis and Modelling at Imperial College. WHO is one of the spearheading partners of GPEI, and provides technical assistance and supports surveillance for acute flaccid paralysis. The Royal Society and the Medical Research Council had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: CM is a serving staff member of the World Health Organization. NG has received funding from the World Health Organization. All other authors have declared that no competing interests exist.
Abbreviations: AIC, Akaike's information criteria; AFP, acute flaccid paralysis; AUC, area under the curve; CI, confidence interval; DRC, the Democratic Republic of the Congo; GPEI, Global Polio Eradication Initiative; OPV, oral poliovirus vaccine; SE, standard error; SIA, supplementary immunisation activity; WHO, World Health Organization
* E-mail: k.oreilly@imperial.ac.uk