Q: My child has a persistent 40°C fever and severe lethargy despite a negative flu test. Should we retest for the flu?

Medically reviewed by Sang Hyun Ahn, MD

Content edited by Myeongchan Kim, MD

This post is a dramatization of a question and answer session experienced by our actual medical reviewers. Please note that this content is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional for any health concerns or before making any decisions related to your health or treatment.

Question:

My child started having a fever around 4 PM on Friday. We managed it overnight with antipyretics; the fever dropped without needing to alternate medications, but it kept returning every 4 to 5 hours. On Saturday at 11 AM, we had a flu test done at the clinic, which came back negative. The doctor diagnosed bronchitis, administered IV fluids, prescribed medication, and we went home.

However, starting around 3 PM on Saturday, my child developed a high fever approaching 40°C along with a phlegmy cough. There has been no improvement with the prescribed medication. My child is severely lethargic, complains of intense body aches, and the fever refuses to drop below 38°C even after taking fever reducers. This is our first time dealing with bronchitis. Can it cause such a continuous, unyielding high fever? Is a retest for the flu necessary?

Answer:

It must be very distressing to see your child struggling so much. The fever that started on Friday has clearly worsened since Saturday afternoon and is no longer responding well to antipyretics.

Based on your description, here is an assessment of the current situation:

• High fever near 40°C that is not responding to fever-reducing medication

• Severe lethargy and noticeable body aches

• New onset of a productive, phlegmy cough

• Symptoms worsening significantly despite an initial negative flu test

A retest for the flu is highly recommended. Rapid flu tests performed within the first 12 to 24 hours of symptom onset can sometimes yield false-negative results because the viral load may not be high enough to detect yet. Given that your child's symptoms are deteriorating and the fever is unresponsive to medication, retesting is the safest course of action.

Please take your child to the emergency room immediately if you observe any of the following red flag symptoms:

• Difficulty breathing or unusually rapid breathing

• Signs of dehydration (such as no urination for more than 8 hours)

• Altered consciousness, severe drowsiness, or very slow responses

Please visit a pediatrician or an urgent care clinic today. You should request a flu retest and also have the doctor evaluate your child for the possibility of pneumonia. While bronchitis can occasionally cause severe symptoms, this sudden and intense worsening requires a prompt, in-person medical evaluation to ensure an accurate diagnosis and proper treatment.

For extra peace of mind and clear guidance when tracking your child's symptoms, the FeverCoach app is always there to help.

https://fevercoach.us