When triaging an infant, which finding would necessitate placing the infant in isolation?

Placing an infant in isolation during triage is critical when there is a purpuric rash present. This finding is particularly concerning as it can indicate serious conditions such as meningococcemia or other severe infections that may be contagious and require immediate medical attention. The purpuric rash, which can appear as petechiae (small purple spots) or larger bruise-like areas, signals that there may be underlying septicemia, which poses a risk of transmission to other patients and healthcare personnel.

While other symptoms like a barking cough, high-pitched cry, or mottled skin may indicate various infections or conditions, they do not possess the same level of infectious risk as a purpuric rash. For instance, a barking cough might suggest croup, and a high-pitched cry could indicate pain or distress without necessarily pointing to an infectious process that is highly communicable. Mottled skin can represent circulatory compromise but again does not imply an immediate risk of contagion like a purpuric rash does. Thus, the presence of a purpuric rash requires isolation to protect others from potential transmission of a severe and contagious condition.