This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Tuberculin test is a cheap and easily available test. In which of the following situations there is high failure in the interpretation of the test? 
Select and explain. 
A. High percentage of immunized people, B. HIV cases are less, C. High prevalence of disease, D. Environmental mycobacterium infections are less
A: High percentage of immunized people
Answer: A: High percentage of immunized people 
Explanation: Ans: A. High percentage of immunized people(Ref Park 24/e p195-196, 23/e p186)High failure of tuberculin test:High percentage of immunized people - Due to higher BCG coverage producing tuberculin hypersensitivity.Exaggerated responses:In presence of atypical mycobacteria infection & 'boosting effect' of second tuberculin dose producing larger reaction than 1st.Tuberculin test lost its sensitivity as an indicator of true prevalence of infection.