[Etiological monitoring and analysis of cases of acute flaccid paralysis in Hebei Province in 2011-2014].

Objective

To identify poliomyelitis(polio)virus, the VP1 gene, and its nucleotide sequence in fecal samples from patients with acute flaccid paralysis(AFP)in Hebei Province in 2011-2014.

Methods

A surveillance system for AFP was established in Hebei Province in 2011-2014 and registered in 2014. Stool samples, each weighing 5 g, were collected from 1 504, 15-year-old symptomatic patients with AFP, resulting in a total of 3 001 samples(1 497 patients provided duplicate samples and 7 provided single specimens). Poliovirus nucleic acid was extracted, the RNA was reverse transcribed, and a VP1 gene fragment was amplified with real-time PCR. The PCR products were sequenced to construct a phylogenetic tree and check the relatedness of the strains to the Sabin vaccine strain. A χ2 test was used to compare the differences in the incidence of infection in different years.

Results

Poliovirus was isolated from 50(1.7%)of the 3 001 stool samples, 10 of which were type Ⅰ strains, 15 were type Ⅱ strains, 16 were type Ⅲ strains, and 9 were mixed-type strains. The positive rates for poliovirus in the years 2011-2014 were 1.0%(9/890), 1.5%(12/824), 2.2%(17/770), and 2.3%(12/517), respectively(χ2=2.24, P=0.525). Analyses of the VP1 nucleotide and amino acid sequence homologies revealed that the type Ⅰ, type Ⅱ, and type Ⅲ poliovirus strains shared nucleotide sequence homologies with the Sabin vaccine strain of 98.8%- 100%, 99.1%- 100%, and 99.2%- 100%, respectively, and amino acid sequence homologies of 98.6%- 100%, 98.3%-100% and 98.6%-100%, respectively. A VP1-based phylogenetic analysis showed that the variation rates for the poliovirus type Ⅰ, type Ⅱ, and type Ⅲ strains were 0.66%, 0.66%, and 0.55%, respectively.

Conclusion

Only one poliovirus strain was detected in Hebei Province in 2011-2014, except for the type Ⅱ vaccine-derived poliovirus. The remaining strains were all similar to the Sabin vaccine strain, with high VP1 homology.