**Question:** Chemoprophylaxis can be done for all of the following infections, except:

A. Pneumococcal pneumonia
B. Tuberculosis
C. Hepatitis B
D. HIV infection

**Correct Answer: D. HIV infection**

**Core Concept:** Chemoprophylaxis is the prevention of infectious diseases by using medication to reduce the risk of infection or to reduce the severity and duration of an infection. This technique is commonly used for infectious diseases caused by bacteria, viruses, or parasites.

**Why the Correct Answer is Right:** Chemoprophylaxis is typically used to prevent or control infections caused by organisms like bacteria, viruses, or parasites. In the case of HIV infection, antiretroviral therapy is used to manage the disease progression rather than prevent it. HIV (Human Immunodeficiency Virus) infects and destroys CD4+ T-cells, which are essential for immune system function. Since HIV is a virus, it cannot be directly targeted by conventional chemoprophylaxis techniques.

**Why Each Wrong Option is Incorrect:**

A. Pneumococcal pneumonia: This is a bacterial infection caused by Streptococcus pneumoniae. Chemoprophylaxis, such as the use of pneumococcal vaccine, can be effective in preventing pneumococcal pneumonia in high-risk individuals.

B. Tuberculosis: Chemoprophylaxis for tuberculosis involves administering antituberculous medications to prevent infection or control progression. This is a common strategy in high-risk groups, such as those with close contact to a tuberculosis patient or those with weakened immune systems.

C. Hepatitis B: Chemoprophylaxis is available for hepatitis B, particularly for newborns of infected mothers or high-risk individuals. Antiviral medications can help prevent the onset of active hepatitis B infection or reduce its severity.

In summary, chemoprophylaxis is effective for preventing or controlling bacterial, viral, and parasitic infections, but it is ineffective for HIV infection due to its nature as a virus and its impact on immune system cells.