Streptococcus pneumoniae, Moraxella catarrhalis and Haemophilus influenzae colonise the nasopharynx of a large proportion of healthy preschool children, and rates are higher still in crowded settings and day care. A swab that grows one of them has established colonisation status, not a diagnosis.
The practical trouble is that the result arrives looking like an answer. A clinician holding a positive culture and an unwell child finds it hard not to treat, and the culture supplies a justification that feels objective. But the same organism would have grown from most of the well children in the waiting room.
The discipline is to decide whether there is an infection on clinical grounds — a focus, a fever pattern, an examination or imaging finding — and to use microbiology to identify the organism once that decision is made, not to make the decision. Where no clinical focus exists, a positive nasopharyngeal result should change nothing.
- Establish the clinical indication for antibiotics before looking at a nasopharyngeal result
- Do not send a nasopharyngeal swab expecting it to decide whether to treat — it cannot
- Where a swab has already come back positive without a focus, document why it is not being acted on
- Explain carriage to parents explicitly; 'the test grew a bacterium' is otherwise heard as 'there is an infection'
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