In which condition would a patient likely experience significant gastrointestinal distress?

Gastroenteritis is characterized by inflammation of the stomach and intestines, often leading to symptoms such as nausea, vomiting, diarrhea, and abdominal pain. This condition is typically caused by infections—viral, bacterial, or parasitic—and is specifically known for causing significant gastrointestinal distress.

It manifests with distress due to the body's response to the inflammation and the irritation of the digestive tract. In contrast, while the other conditions mentioned may have their own set of symptoms, they do not primarily involve gastrointestinal complications. For instance, carditis involves inflammation of the heart, pneumonitis affects the lungs, and nephritis pertains to inflammation of the kidneys, all of which do not produce the same level of gastrointestinal issues as gastroenteritis does.