Analysis on virological surveillance of acute flaccid paralysis in Chongqing (2008-2011)

Objective To evaluate the surveillance system of the acute flaccid paralysis(AFP)cases in Chongqing from 2008 to 2011.Methods Viruses were isolated and identified according to the Polio Laboratory Manual,and the results were conducted intratypic differentiation at the National Poliomyelitis Laboratory by PCR-RFLP and ELISA methods.Results 10 strains of poliomyelitis virus(PV)were isolated from human fecal samples of 307 AFP cases,The isolating rate was 3.26%,which included 5 strains of the type Ⅱ poliovirus,3 strains of the type III poliovirus and 2 strains of the mixed poliovirus.The principle prevalent type was Ⅱ,accounted for 50.00%,followed by type Ⅲ and PV hybrid,accounted for 30.00% and 20.00% respectively.All the PVs were sent to the National Poliomyelitis Laboratory for further intratypic differentiation and identification.The results indicated that 9 strains were vaccine-related.Meanwhile,6 nucleotide sequence variations were found in 1 strain of the type Ⅱ poliovirus,which was confirmed as the pre-vaccine-derived poliovirus(pre-VDPV).26 strains of non-polio enterovirus were also isolated.,The isolating rate was 8.47%.Conclusions From 2008 to 2011 in Chongqing,no wild polio virus was isolated from the acute flaccid paralysis cases,which meant Chongqing remain polio-free area.However,the surveillance of AFP cases should be continued to ensure reaching the target of poliomyelitis eradication all over the world.