'Find the case record for a person for a disease
@param person_id: the person record ID
@param disease_id: the disease record ID'

@staticmethod
def get_case(person_id, disease_id):

    ctable = current.s3db.disease_case
    query = (((ctable.person_id == person_id) & (ctable.disease_id == disease_id)) & (ctable.deleted != True))
    record = current.db(query).select(ctable.id, ctable.case_number, limitby=(0, 1)).first()
    return record
