A nurse is implementing a plan of care for a client who has AIDS with recurring pneumonia. Which of the following actions should the nurse take?

When a client with AIDS has recurring pneumonia, obtaining a sputum culture is the priority nursing action because it identifies the causative organism and guides appropriate antibiotic or antifungal therapy. Clients with AIDS are susceptible to opportunistic pneumonias such as Pneumocystis jirovecii pneumonia, bacterial pneumonia, and fungal infections, so pathogen identification directly informs treatment decisions. Coughing and deep breathing every 8 hours is insufficient frequency — respiratory hygiene measures should generally be performed every 2 hours to promote airway clearance and prevent mucus stasis. Positioning the head of bed at only 10 degrees is incorrect and potentially harmful; the head of the bed should be elevated to at least 30–45 degrees to facilitate lung expansion, reduce aspiration risk, and improve oxygenation. Encouraging fluid intake of 1,500 mL per day is below the recommended level for a client with pneumonia; adequate hydration (typically 2,000–3,000 mL per day unless contraindicated) helps thin secretions and facilitate expectoration. Therefore, obtaining a sputum culture provides the clinical data needed to direct targeted treatment, making it the most appropriate and priority nursing action among the options given.