Investigations of clinical isolations of oral poliovirus vaccine strains between 2000 and 2005 in southern Taiwan

Background: In Taiwan, trivalent oral poliovirus vaccine (tOPV) is in the routine immunization schedule, but its association with illnesses had not been examined. Objectives: To investigate clinical presentations and viral characteristics of patients with poliovirus isolates. Study design: Clinical data, vaccination records and viral sequences were retrospectively analyzed for patients from whom polioviruses were isolated during 2000-2005. Results: OPV-like strains were the only pathogen identified in 208 children who were diagnosed with lower respiratory tract infection (24.5%), acute gastroenteritis (16.8%) or upper respiratory tract infection (10.6%). Timing of poliovirus isolation relative to the tOPV vaccination was unusual in 59 patients, including 6 before any dose and 53 more than 10 weeks after the 3rd or later dose of tOPV. Sequence analyses of the VP1, 2C and 3C/D regions for 19 poliovirus isolates revealed that 4 had previously reported neurovirulence reversions, 1 had intertypic recombination, and 6 had both. No patient had neurological complications, but 3 died of myocarditis, including 2 with recombinant strains and 1 who never received OPV. Conclusion: This study describes the isolation of OPV-like strains from patients with a variety of illnesses, raising concerns about their pathogenic potential in an area where tOPV is routinely administered. The detection of genetic variations among OPV-like strains warrants continuing surveillance for these variants in patients with severe illnesses besides neurological complications.