The most common causative agents of bacterial meningitis are:

Correct Answer: B

Rationale: The correct answer is B because Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae are the most common causative agents of bacterial meningitis. Streptococcus pneumoniae is a leading cause in adults, Neisseria meningitidis is common in adolescents and young adults, and Haemophilus influenzae is more frequent in children. The other choices, Rubella virus (C) and Herpangina (D), are not bacterial agents known to cause meningitis.

Correct Answer: D

Rationale: The correct answer is D, Formation of CD4+ cells. In autoimmune reactions, CD4+ cells are actually involved in the immune response. Here's the rationale: 1. CD4+ cells are helper T cells that play a crucial role in activating other immune cells in autoimmune reactions. 2. Decreased functional activity of T-suppressors (Choice A) is typical in autoimmune reactions as it leads to unchecked immune responses. 3. Loss of tolerance for T-helpers and B-lymphocytes (Choice B) is common in autoimmune reactions, where the immune system mistakenly attacks self-cells. 4. Ag released by normally isolated tissues (Choice C) is a typical mechanism in autoimmune reactions where self-antigens trigger immune responses.

Correct Answer: A

Rationale: The correct answer is A: Staphylococcus saprophyticus. This bacterium is the second most common cause of cystitis in healthy sexually active women after E. coli. Staphylococcus saprophyticus is commonly found in the gastrointestinal and genital areas. It has a unique ability to adhere to uroepithelial cells, making it a common pathogen in urinary tract infections. Proteus mirabilis is more commonly associated with complicated UTIs, especially in catheterized patients. Pseudomonas aeruginosa is more commonly seen in hospitalized or immunocompromised patients. Klebsiella pneumoniae is typically associated with UTIs in elderly patients or those with structural abnormalities in the urinary tract.

Correct Answer: B

Rationale: The correct answer is B: FALSE. Adenoviral infections are not restricted only to the upper respiratory tract; they can also affect the gastrointestinal tract, eyes, and other organs. Adenoviruses are known to cause a wide range of illnesses beyond just respiratory infections. Therefore, option B is correct. Option A is incorrect because it states that adenoviral infections are restricted to the upper respiratory tract, which is not true. Option C is incorrect because there is no circumstance where adenoviral infections are solely limited to the upper respiratory tract. Option D is also incorrect as the correct answer is B.

Correct Answer: D

Rationale: The correct answer is D: Exanthematous rash. Erythema infectiosum, also known as fifth disease, is characterized by a distinctive rash on the cheeks that looks like a "slapped cheek." This rash then spreads to the rest of the body, resulting in a lace-like rash (exanthem). Swelling of salivary glands (choice A) is not a typical symptom of erythema infectiosum. Diarrhea (choice B) and hepatitis (choice C) are also not associated with this condition. Therefore, the most characteristic clinical symptom of erythema infectiosum is the exanthematous rash.