The overall number of cases of STIs is:

Choice A reason: CD4 counts are not used to detect HIV, but to monitor the progression of the infection and the immune system status. CD4 cells are a type of white blood cell that HIV targets and destroys. A normal CD4 count ranges from 500 to 1,500 cells per microliter of blood. A low CD4 count indicates a high risk of opportunistic infections and AIDS.

Choice B reason: Virus is a vague term that does not specify what kind of virus is being detected. HIV is a type of virus that belongs to the retrovirus family. It is difficult to detect the virus itself, as it hides inside the host cells and has a low concentration in the blood. Therefore, most laboratory tests focus on the antibodies that the body produces in response to the virus.

Choice C reason: HIV antibodies are the most common way to detect HIV, as they are produced by the immune system to fight the virus. Antibodies are proteins that bind to specific antigens (foreign substances) and mark them for destruction. HIV antibodies can be detected by a blood test, a saliva test, or a rapid test. However, antibodies may take several weeks to develop after exposure, so a negative test does not rule out the possibility of infection.

Choice D reason: CD8 counts are not used to detect HIV, but to monitor the immune system response and the viral load. CD8 cells are a type of white blood cell that kill infected cells and secrete antiviral substances. A high CD8 count indicates a strong immune response and a low viral load. A low CD8 count indicates a weak immune response and a high viral load.

Choice A reason: Human papillomavirus is incorrect because it is not caused by a bacterium, but by a virus. It can cause genital warts and cervical cancer, but it cannot be cured with antibiotics.

Choice B reason: Gonorrhea is correct because it is caused by a bacterium called Neisseria gonorrhoeae, often produces no symptoms, but can be treated with antibiotics. If symptoms occur, they may include painful urination and discharge from the penis or vagina. If left untreated, the infection can result in more serious long-term problems, including infertility, pain, and joint problems.

Choice C reason: Herpes simplex virus is incorrect because it is not caused by a bacterium, but by a virus. It can cause genital herpes, which is marked by painful blisters and sores in the genital area. It cannot be cured with antibiotics, but antiviral medications can help reduce the frequency and severity of outbreaks.

Choice D reason: Cytomegalovirus is incorrect because it is not caused by a bacterium, but by a virus. It usually causes mild or no symptoms in healthy people, but can be serious in people with weakened immune systems or unborn babies. It cannot be cured with antibiotics, but antiviral medications can help treat the symptoms.