What symptom would warrant calling 9-1-1 for a swimmer with a history of allergies?

The symptom that warrants calling 9-1-1 for a swimmer with a history of allergies is difficulty in breathing. This symptom is particularly concerning because it can indicate a severe allergic reaction, known as anaphylaxis, which may lead to airway constriction and a lack of oxygen. When someone experiences difficulty breathing, it poses an immediate and significant risk to their health and well-being, necessitating emergency medical attention.

In contrast, while tightness in the throat can also suggest an impending respiratory issue, the phrasing may be more symptomatically vague compared to direct breathing difficulties. A rash on the skin and itchy eyes, though potentially uncomfortable and indicative of an allergic reaction, typically do not pose the same level of immediate danger as breathing difficulties. Hence, in an emergency situation, the priority is to address symptoms that directly threaten the swimmer's safety, which is why difficulty in breathing is the key symptom that requires calling 9-1-1.