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[Polio virus detection in stool by the pathogen surveillance system of Japan. An observational study].

OBJECTIVES
To examine the applicability of data on polio virus detection in stool by the Pathogen Surveillance System of Japan (PSSJ) for the evaluation of polio virus retention status in a regional community after oral polio vaccination (OPV).


METHODS
(1) Data for the city of Kobe (part of the PSSJ data): Cases of polio virus detection in stool reported to Kobe City Public Health Center from January 1, 2000 to June 30, 2010 were examined regarding time duration from vaccination to detection as well as age and gender. (2) PSSJ data: Cases of polio virus detection in stool reported to PSSJ from January 1, 2000 to December 31, 2010 were examined regarding the serological types of the virus as well as age and gender. A logistic regression analysis was used to derive odds ratios for the relationship between age and serological type of polio virus in stool.


RESULTS
Thirty-one cases (33 stool samples) were identified in the Kobe city data. Of these, 96.8% were in children two years old or younger and 54.8% were girls. The time duration between vaccination and detection of all the cases was within two months from vaccination. From the PSSJ data, 852 cases were identified. Of these, 97.3% were two years old or younger and 54.6% were girls. The proportion of serological types was different by age group: for those under one year old, the type 1 virus accounted for 33.2%; type 2, 44.8%; and type 3, 22.0%. In the one year old or older age group, these types accounted for 22.8%, 27.6% and 49.6%, respectively. Notably, the type 3 virus was detected more for the older age group. (odds ratio 3.4, 95% confidence interval 2.5-4.6).


CONCLUSION
The duration before detection and the serological types of polio virus in stool from the PSSJ and Kobe City data are consistent with the results of the prior studies that have evaluated the shedding of polio virus in stool after the administration of OPV. Since the PSSJ data are collected from a relatively wide range of samples, we conclude that the PSSJ data accurately represent polio virus retention status in a regional community after OPV. The current situation of polio virus shedding in stool cannot be ignored, and further consideration needs to be given to improving the accuracy of the PSSJ data, because Japan is to switch over to inactive polio vaccines in the near future.