Which of the following is an early sign of pneumonia?

Cough is considered an early sign of pneumonia because it is one of the initial respiratory symptoms that patients typically experience when an infection in the lungs begins to develop. The cough associated with pneumonia can be either dry or productive, often producing sputum as the condition progresses. The presence of a cough indicates irritation in the airways or lung tissue, which commonly occurs with an infectious process such as pneumonia.

In contrast, pleural effusion, hemoptysis, and fever may develop as the condition worsens or in response to pneumonia but are not typically considered early signs. Pleural effusion can occur as a complication of pneumonia but does not present immediately. Hemoptysis, or coughing up blood, is more indicative of a severe or advanced stage of pulmonary issues rather than an early symptom. Fever is often present in pneumonia, but it may not always manifest in the early stages, particularly in elderly patients or those who are immunocompromised. Therefore, the cough stands out as an early indicator of respiratory infection leading towards pneumonia.