A 3yo boy with hx of recurrent upper respiratory infections and chronic diarrhea is brought ot physician because of weight loss, irritability, fever, and a productive cough. Physical exam shows intercostal retractions and wheezing and rhonci are heard on auscultation of chest. Nose exam shows nasal polyps. CXR shows patchy infiltrates and atelectasis. Gram stain and culture of sputum shows non-lactose fermenting gram negative rods. 1.What is the most likely underlying pathology in this child and why? 2. What is the likely causal organism for his infection and why? 3. What is most important pathogenic attribute of this organism?

The main function of the respiratory system is gas exchange (O2 and CO2). Ventilation is the movement of air through the respiratory tract into (inspiration) and out of (expiration) the respiratory zone (lungs).