Which type of same can be used to isolate polio virus earliest

Stool examination Isolation of wild polio virus from stool is 'the recommended method for laboratory confirmation of paralytic poliomyelitis' Recommended in every case of AFP Virus usually can be found in the feces from onset to up to <8 weeks after paralysis, with the highest probability of detection during the first 2 weeks after paralysis onset Ref : Park 25th edition Pgno : 223