In this question, we need to determine the most characteristic symptom of infectious esophagitis. Let's analyze the given options to identify the correct answer:

• Dysphagia: This term refers to difficulty in swallowing. While dysphagia can occur in esophagitis, it is not the most characteristic symptom specifically for infectious esophagitis.
• Chest pain: Although chest pain can be associated with esophagitis, it is a less specific symptom and often overlaps with other conditions such as cardiac issues.
• Odynophagia: This is defined as painful swallowing and is the most characteristic symptom of infectious esophagitis. The pain occurs as the esophagus becomes inflamed and irritated due to the infection.
• Haematemesis: It involves vomiting blood and is typically associated with severe conditions affecting the gastrointestinal tract, like a bleeding ulcer, rather than being a primary symptom of infectious esophagitis.

Based on the explanations above, Odynophagia is the correct answer because it is the most characteristic symptom of infectious esophagitis. The inflammation and infection of the esophageal lining lead to pain when swallowing, making it the hallmark symptom in such cases.