A statistical model demonstrated that bordering Nigeria (IRR 5.39) and poliovirus exposure from infected countries were strongly associated with poliomyelitis outbreaks, enabling 6-month-ahead forecasts with 82% predictive ability.
Observational
A statistical model incorporating population movement and childhood mortality can predict the geographical risk of poliomyelitis outbreaks in Africa with 82% accuracy, which can guide targeted immunisation planning.
Effect estimate: IRR 5.39 (95% CI 2.69-10.78)
p-value: p=<0.001
BACKGROUND: Outbreaks of poliomyelitis in African countries that were previously free of wild-type poliovirus cost the Global Polio Eradication Initiative US850 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.
O’Reilly et al. (Tue,) conducted a observational in Poliomyelitis outbreaks. Country borders Nigeria vs. Country does not border Nigeria was evaluated on Number of poliomyelitis outbreaks (IRR 5.39, 95% CI 2.69-10.78, p=<0.001). A statistical model demonstrated that bordering Nigeria (IRR 5.39) and poliovirus exposure from infected countries were strongly associated with poliomyelitis outbreaks, enabling 6-month-ahead forecasts with 82% predictive ability.