A dynamic model of poliomyelitis outbreaks: learning from the past to help inform the future.

Policy-makers now face important questions regarding the tradeoffs among different strategies for managing poliomyelitis risks after they succeed with polio eradication. To estimate the potential consequences of reintroductions of polioviruses and the resulting outbreaks, the authors developed a dynamic disease transmission model that can simulate many aspects of outbreaks for different posteradication conditions. In this paper, the authors identify the issues related to prospective modeling of future outbreaks using such a model, including the reality that accurate prediction of conditions and associated model inputs prior to future outbreaks remains challenging. The authors explored the model's behavior in the context of three recent outbreaks resulting from importation of poliovirus into previously polio-free countries and found that the model reproduced reported data on the incidence of cases. The authors expect that this model can provide important insights into the dynamics of future potential poliomyelitis outbreaks and in this way serve as a useful tool for risk assessment.

Isolation and characterization of circulating type 1 vaccine-derived poliovirus from sewage and stream waters in Hispaniola.

Twenty-one cases of acute flaccid paralysis (AFP) were reported on the island of Hispaniola in 2000. Laboratory analysis confirmed the presence of circulating vaccine-derived poliovirus (cVDPV) type 1 in stool samples obtained from patients. As a complement to the active search for cases of AFP, environmental sampling was conducted during November and December 2000, to test for cVDPV in sewage, streams, canals, and public latrines. Fifty-five environmental samples were obtained and analyzed for the presence of polioviruses by use of cell culture followed by neutralization and reverse-transcription polymerase chain reaction. Of the 23 positive samples, 10 tested positive for poliovirus type 1, 7 tested positive for poliovirus type 2, 5 tested positive for poliovirus type 3, and 1 tested positive for both poliovirus type 2 and type 3. By sequence analysis of the complete viral capsid gene 1 (VP1), a 2.1%-3.7% genetic sequence difference between 7 type 1 strains and Sabin type 1 vaccine strain was found. Phylogenetic analysis showed that these viruses are highly related to cVDPV isolated from clinical cases and form distinct subclusters related to geographic region. Our findings demonstrate a useful role for environmental surveillance of neurovirulent polioviruses in the overall polio eradication program.