Medical Definition of persistent
1: existing or continuing for a long time: asa: effective in the open for an appreciable time usually through slow volatilizing <mustard gas is persistent>b: degraded only slowly by the environment <persistent pesticides>c: remaining infective for a relatively long time in a vector after an initial period of incubation <persistent viruses>
2: continuing to exist despite interference or treatment <a persistent cough> <has been in a persistent vegetative state for two years>
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