def disease_term(self, disease_identifier):
        """Return a disease term

        Checks if the identifier is a disease number or a id

        Args:
            disease_identifier(str)

        Returns:
            disease_obj(dict)
        """
        query = {}
        try:
            disease_identifier = int(disease_identifier)
            query['disease_nr'] = disease_identifier
        except ValueError:
            query['_id'] = disease_identifier

        return self.disease_term_collection.find_one(query)