Q: My 5-year-old had high fever and two negative flu tests, but now his sibling has the flu. Should we test again?
- Myeongchan Kim, MD
- Jun 19
- 3 min read
Updated: Jul 8
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:
I have a question regarding the flu for my 5-year-old son. His temperature logs are as follows:
Saturday morning: 39.5°C
Sunday: 39°C - 40°C (Flu test was negative, took fever reducers)
Monday: Continued at 39.5°C (Flu test was negative, took fever reducers)
Tuesday: Mild fever, occasionally normal temperature (No medication)
Wednesday: 38°C
He also has a runny nose, phlegm, and a cough. Should we retest him for the flu? Would a test even show a positive result at this point? His older sibling was at home all last week but was officially diagnosed with the flu today. I suspect the younger one had the flu and passed it to the older sibling.
Answer:
It must have been very worrying to see your child with a high fever since Saturday.
Current Situation Summary:
High fever (39–40°C) from Saturday to Monday, which dropped to a mild fever (up to 38°C) starting Tuesday.
Accompanied by a runny nose, phlegm, and coughing.
Negative flu tests on Sunday and Monday, but a sibling has now been confirmed to have the flu.
Should You Retest for the Flu?
While it is relatively uncommon for a test to turn positive after initial negative results, given the sibling's confirmed diagnosis and your son's symptom pattern, a pediatrician might make a clinical diagnosis of the flu (without needing another test) or consider retesting.
As of Wednesday (day 4-5 of the illness), the sensitivity of a rapid flu test may be lower than in the initial stages. However, a doctor will make a judgment based on both his symptoms and the history of household contact.
Home Care Guidelines:
Offer fluids frequently in small amounts to prevent dehydration.
Dress him in light clothing and keep the room at a comfortable temperature.
Use fever reducers only when the child is uncomfortable (a mild fever around 38°C does not necessarily require medication if he is active).
Use saline nasal drops and maintain indoor humidity (40-60%) to help alleviate the runny nose and loosen phlegm.
When to Seek Immediate Medical Attention:
Please visit a doctor today if you observe any of the following:
His breathing becomes fast or he appears to have difficulty breathing.
He refuses all fluids and food, and has no urine output for over 8 hours.
He suddenly becomes severely lethargic or difficult to wake.
The high fever (39°C or above) returns and persists.
Actionable Guidance:
If his fever is trending downward and he is comfortable, observing his condition at home is generally acceptable. However, because his sibling has officially been diagnosed with the flu, it is safest to visit your pediatrician's office. You should consult with the doctor to determine if a clinical flu diagnosis can be made, whether a retest or antiviral medication is necessary at this stage, or if simply monitoring his improving symptoms is sufficient.
For extra peace of mind and clear guidance when tracking your child's symptoms, the FeverCoach app is always there to help.
