The baby has a low-grade fever at night but is normal during the day.

A baby who develops a low-grade fever only at night while remaining normal during the day may be experiencing either non-disease-related factors or conditions such as bronchitis or pneumonia.

1. Non-disease factors

This could occur because the body's temperature regulation functions well during the day, allowing self-regulation, but noticeably declines during nighttime sleep, leading to a slight fever. This condition usually resolves on its own.

2. Disease factors

1) Bronchitis

This may be caused by a viral infection triggering bronchitis, with extensive viral replication occurring in the bronchi. Treatment may include ribavirin granules, anti-viral oral liquid, or ganciclovir granules, used according to medical advice.

2) Pneumonia

This could result from a bacterial infection causing pneumonia, leading to inflammation of the alveoli and lung interstitium, which affects the body's temperature regulation center. Treatment may include azithromycin dispersible tablets, roxithromycin dispersible tablets, or clindamycin capsules, taken under a doctor's guidance.

In addition, tuberculosis could also be a possible cause. It is recommended to seek timely medical evaluation to determine the underlying cause and receive appropriate treatment.