Final answer:
Observation may be appropriate for an isolated, newly discovered, enlarged cervical lymph node if it is likely due to a mild infection and resolves within a few weeks. Persistent or accompanied by symptoms lymph nodes warrant further investigation. Immediate attention is necessary when systemic infection signs are present, as shown by Olivia's case.
Step-by-step explanation:
Observation is acceptable for a newly discovered, isolated, enlarged cervical lymph node when it is likely a reaction to a mild, unnoticed infection and there are no other concerning symptoms. Generally, if the enlargement reduces back to normal size within a few weeks, it is not a cause for concern.
However, persistent swelling, especially with additional symptoms or without signs of a recent infection, should be investigated further with medical examinations such as a biopsy, as in the case of Wei who continued to experience enlargement after treatment with antibiotics. In contrast, the scenario with Olivia indicates a systemic infection given her symptoms and abnormal laboratory findings, requiring immediate medical attention.