MERGE (c:contact {guid : '500010'})
ON CREATE SET
    c.data_source = '1',
    c.guid = '500010',
    c.created = timestamp()
ON MATCH SET
    c.lastUpdated = timestamp()
MERGE (s:speciality {specialtygroup_desc : 'cold'})
ON CREATE SET s.data_source = '1',
    s.specialtygroup_desc = 'fever',
    s.created = timestamp()
ON MATCH SET s.data_source = '1',
    s.specialtygroup_desc = 'comman cold',
    s.lastUpdated = timestamp()
MERGE (c)-[r:is_specialised_in]->(s)
ON CREATE SET
    r.duration = 1
ON MATCH SET
    r.duration = r.duration + 1

On the first run, node is created as "fever". On the second run, I have updated the specialty_group to "common cold". But it is creating new node with "fever". I am not able to update the "fever" to "common cold". What changes should I make to the above query?