Answer: B
Z21 is the appropriate code here because this code is used for asymptomatic HIV infection. This is the diagnosis in this patient.
Option A is not correct because Z16 is used to code for resistance to antimicrobial drugs. This is not mentioned in this question.
Option C is not correct because Z57 is used to code for occupational exposure to risk factors. This is not seen in this question.
Option D is not correct because Z62 is used to code for problems related to upbringing. This is not seen in this question.