Infectious diseases in the adult population are responsible for about one third of all deaths in individuals over the age of:

Correct Answer: C

Rationale: The correct answer is C (60 years) because as individuals age, their immune system weakens, making them more susceptible to infectious diseases. Around the age of 60, people are more likely to succumb to infections, leading to a higher mortality rate. Choices A, B, and D are incorrect because they are younger ages, and the likelihood of infectious diseases causing a significant proportion of deaths increases with age.

Correct Answer: D

Rationale: The correct answer is D: salmonellosis. Zoonotic diseases are those that can be transmitted from animals to humans. Salmonella is not directly transmitted from animals to humans, instead, it is typically transmitted through contaminated food or water. Brucellosis (A), undulant fever (B), and plague (C) are all zoonotic diseases that can be directly transmitted from animals to humans through various means. Therefore, salmonellosis does not fit the definition of a zoonotic disease, making it the correct answer.

Correct Answer: B

Rationale: The correct answer is B because the capsule of bacteria is mainly composed of polysaccharides or polypeptides. This outer layer helps bacteria evade the host's immune system and protects them from desiccation. Peptidoglycan (choice A) is a component of the bacterial cell wall, not the capsule. Flagellin (choice C) is a protein component of the bacterial flagella, not the capsule. Choice D is incorrect as the capsule is indeed composed of polysaccharides or polypeptides.

Correct Answer: D

Rationale: The correct answer is D: mixed infection. In a mixed infection, multiple infectious agents establish themselves at the same site, leading to a complex and diverse infection. This type of infection can involve different types of pathogens such as bacteria, viruses, fungi, and parasites. It can be challenging to diagnose and treat due to the presence of multiple pathogens. A: Chronic infection refers to an infection that persists over a long period but is typically caused by a single pathogen. B: Necrotizing infection is characterized by rapid tissue destruction but does not necessarily involve multiple infectious agents. C: Fatal infection does not specify the presence of multiple infectious agents, it simply implies that the infection leads to death. In summary, the correct answer, mixed infection, is the only choice that specifically describes the scenario of multiple infectious agents establishing themselves at the same site.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is the most likely causative agent because it is a Gram-positive cocci in pairs with a capsule, which matches the description provided. S. pneumoniae is a common cause of bacterial pharyngitis and can present with sore throat. Summary of other choices: B: Staphylococcus aureus is a Gram-positive cocci in clusters, not pairs, and is not typically associated with sore throat. C: Neisseria meningitidis is a Gram-negative diplococcus and more commonly causes meningitis or septicemia, not sore throat. D: Klebsiella pneumoniae is a Gram-negative rod bacterium, not a Gram-positive cocci, and is not a common cause of sore throat.

Correct Answer: A

Rationale: The correct answer is A: Salk and Sabin vaccines are vaccines against polio. Both Salk and Sabin vaccines are indeed vaccines specifically developed to prevent polio. The Salk vaccine is an inactivated polio vaccine, while the Sabin vaccine is an oral live attenuated vaccine. Therefore, choice B is incorrect as the Sabin vaccine is live attenuated, not inactivated. Choice C is also incorrect because the Salk vaccine is inactivated, not live attenuated. Choice D is incorrect because not all statements are true; only statement A is accurate.

Correct Answer: A

Rationale: The correct answer is A: Pertussis bacillus. The symptoms described - elevated temperature and typical cough - are indicative of whooping cough, caused by Bordetella pertussis. By inoculating mucus from the nasopharynx on agar, the doctor is trying to isolate the causative agent, which is likely to be Pertussis bacillus. Summary of other choices: B: Pfeiffer's bacillus (Haemophilus influenzae): Unlikely as symptoms do not match. C: Listeria: Unlikely as it typically causes foodborne illness, not respiratory infections. D: Klebsiella: Unlikely as it is more commonly associated with pneumonia in immunocompromised individuals.

Correct Answer: B

Rationale: The correct answer is B: Legionella and Neisseria are both gram-negative aerobic rods and cocci. Legionella is a rod-shaped bacterium, while Neisseria is a diplococcus. Both are aerobic, meaning they require oxygen for growth. The other choices are incorrect because Legionella and Neisseria are not facultative anaerobes (A), spirochetes (C), or anaerobic cocci (D). Understanding the characteristics of these bacteria helps in differentiating and selecting the correct answer.

Correct Answer: B

Rationale: The correct answer is B: CDC. The Centers for Disease Control and Prevention (CDC) is responsible for establishing hand-washing guidelines in healthcare settings to prevent infections. CDC is a leading authority in public health and provides evidence-based recommendations. OSHA (A) focuses on workplace safety, NIAD (C) is not a recognized organization, and WHO (D) provides global health guidelines but CDC is the primary authority for hand hygiene in the US healthcare system.