Correct Answer: B

Rationale: The correct statements about secondary immunodeficiencies are that they may develop after viral infections, following immunosuppressive therapies, and are caused by superimposed conditions. Choice B ('Develop before birth') is incorrect because secondary immunodeficiencies do not develop before birth. They are acquired later in life. Therefore, the correct answers are A, C, and D.

Correct Answer: C

Rationale: The correct answer is C. In emphysema, impaired oxygenation results from enlarged and permanently inflated alveoli, leading to reduced surface area for gas exchange. Choices A, B, and D are incorrect. In emphysema, bronchioles are not typically filled with mucus, alveoli losing surfactant and collapsing is more characteristic of conditions like atelectasis, and purulent fluid accumulation in the bronchioles is commonly seen in conditions like pneumonia, not emphysema.

Correct Answer: A

Rationale: The correct answer is Clarithromycin. Clarithromycin is one of the recommended medications for treating Mycobacterium avium complex (MAC) infections in patients with HIV. It is a macrolide antibiotic that is effective against MAC. Isoniazid (INH) is used to treat tuberculosis, not MAC. Rifabutin is another medication used in the treatment of MAC infections, but clarithromycin is preferred as a first-line agent. Azithromycin is also used in the treatment of MAC infections; however, clarithromycin is more commonly recommended due to its efficacy and safety profile.

Correct Answer: A

Rationale: The correct answer is A: 'Bronchospasm after exercise.' Exercise-induced asthma involves the narrowing of the airways (bronchospasm) triggered by physical activity. This bronchospasm leads to symptoms such as coughing, wheezing, and shortness of breath. Choices B, C, and D are incorrect because exercise-induced asthma is not primarily caused by an IgE-mediated inflammatory response to an antigen, bronchoconstriction after ingesting high-allergen foods, or increased mucus production due to a genetic mutation.

Correct Answer: C

Rationale: The correct answer is C. The administration of live vaccines may be contraindicated in patients taking steroid therapy. Steroids can suppress the immune system, reducing the effectiveness of live vaccines. Patients with renal insufficiency or hepatic failure can typically receive live vaccines as these conditions are not direct contraindications. Age alone, such as being over 65 years old, is not a contraindication for live vaccines unless there are other specific health considerations. Therefore, the patient taking steroid therapy is the most likely candidate for whom the administration of a live vaccine would be contraindicated.