Final answer:
The nurse should use airborne precautions for a patient with pulmonary tuberculosis to prevent the spread of the infection through the air.
Step-by-step explanation:
The correct precaution for a nurse to begin for an older adult with pulmonary tuberculosis is airborne precautions. Tuberculosis (TB) is known to be spread through the inhalation of droplet nuclei containing tubercle bacilli, which can then travel to the alveoli of the lungs. Airborne precautions include the use of a high-efficiency particulate air (HEPA) mask for the healthcare provider and placing the patient in a negative pressure room if possible. This is to prevent the spread of the infection through the air, as TB can be easily transmitted through coughing, sneezing, or spitting.