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Dark grey to black stools can indicate upper gastrointestinal bleeding
or severe infection viral or malarial or a sideeffectof medications.
Since your child was ill with bronchiolitis
, and still running fever it is advisable to consult her treating pediatrician
and get few investigations done like
1.complete blood counts & blood culture
to rule out low platelet counts or sepsis
2.blood smear to rule out malarial parasites.
3 repeat chest xrays to rule out worsening of bronchiolitis.
4 stool routine and culture.
This will confirm the cause of her persistent fever and black stools and appropriate management can be started.
If she is taking any iron or multivitamins containing medications as per prescription then it's just black discolouration of the normal stools and you need not worry.
If sideeffects of medications are ruled out then please consult her doctor for reevaluation or atleast get her stool test
done to be on the safer side.
Please do not hesitate to discuss her condition with the treating doctor.
Also most bronchiolitis cases take 10 days to recover and since she is under treatment you should not worry.Hope she has a speedy recovery .
Wishing her good health forever.