Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The heart size is normal with mild tortuosity of the thoracic aorta . Hilar contours are unremarkable . Subtle increased density of the left lung base compared to prior examination is worrisome for infection . The right lung is clear . There is no pleural effusion or pneumothorax .
    OUTPUT:
    
Subtle increased opacity of the left lung base worrisome for infection .