Which of the following indicates severe heat-related illness?

High body temperature with confusion indicates a severe heat-related illness, such as heat stroke. This condition occurs when the body overheats, and it can lead to serious health complications if not treated promptly. The presence of confusion signifies that the body's normal thermoregulatory processes have become overwhelmed, affecting the brain's function. Elevated body temperature, typically above 104°F (40°C), alongside neurological symptoms like confusion, disorientation, or altered mental status, is a critical warning sign that immediate medical intervention is necessary.

In contrast, the other options listed represent less severe conditions. A persistent headache can result from dehydration but doesn't necessarily indicate a severe heat illness on its own. Sunburn is an injury to the skin caused by excessive sun exposure, and while it is a concern, it does not indicate systemic heat stress. Temporary fatigue is often associated with heat exposure and can be a sign of heat exhaustion, but it generally lacks the immediate danger that confusion and high body temperature signify. Therefore, recognizing high body temperature accompanied by confusion is essential for identifying and responding to a severe heat-related illness effectively.