Pneumonia: This is the most common cause of a patchy infiltrate on a chest radiograph. The left basilar region is a typical location for aspiration pneumonia or community-acquired pneumonia, especially in the context of symptoms like cough, fever, and shortness of breath.

Atelectasis: This condition, which involves the collapse or closure of a lung resulting in reduced or absent gas exchange, can present with similar radiographic findings. It is often seen post-operatively or in patients who are bedridden and have poor respiratory effort.
Pulmonary Edema: While typically more diffuse, pulmonary edema can present with patchy infiltrates, especially in the basilar regions. It is often associated with heart failure or fluid overload.
Chronic Interstitial Lung Disease: Conditions like idiopathic pulmonary fibrosis can present with patchy infiltrates, although these are usually more diffuse and bilateral.

Pulmonary Embolism: Although pulmonary embolism typically presents with more dramatic symptoms and may not always show clear infiltrates on a chest X-ray, it can sometimes cause infarction leading to a patchy infiltrate. Missing this diagnosis can be fatal.
Tuberculosis: Especially in endemic areas or in immunocompromised patients, tuberculosis can present with patchy infiltrates and must be considered to prevent missing a potentially treatable condition.

Lymphangitic Carcinomatosis: A rare condition where cancer spreads to the lymphatic vessels of the lungs, causing interstitial infiltrates.
Eosinophilic Pneumonia: A rare condition characterized by an accumulation of eosinophils in the lungs, which can present with patchy infiltrates.
Cryptogenic Organizing Pneumonia (COP): A rare condition that can present with patchy infiltrates and is characterized by the presence of organizing pneumonia on histopathology.