My 2 & a half year old son has had hfm 5 times!! why is this reoccurring? do i need to investigate further?

Likely mislabeled: I can think of 2 to 3 strains of enterviruses that will give the HFM syndrome,after each,long term immunity to that strain would be expected.The syndrome can present with isolated blisters on just one,more than one or all of 4 areas (HFM and around the anus).Since lab testing is rarely done, the label may be overused on a condition that mimics HFM.A consult with infectious disease may help.