Infectious Diseases Practice Questions

Q: Mycobacterium avium complex infections are common when the CD4+ counts in cells/mm3 are?

< 50. ***< 50*** - **_Mycobacterium avium_ complex (MAC)** infections are considered an **AIDS-defining illness** and typically occur in individuals with advanced immunosuppression. - The threshold for primary prophylaxis against MAC is a **CD4+ count below 50 cells/mm3**, indicating a severely compromised immune system. *< 100* - While a **CD4+ count below 100 cells/mm3** signifies severe immunosuppression, the specific threshold for MAC infection risk and prophylaxis initiation is generally lower. - At this level, opportunistic infections like **Pneumocystis pneumonia** and **Toxoplasmosis** are more common, though MAC risk is also elevated. *< 200* - A **CD4+ count below 200 cells/mm3** is significant as it defines **AIDS** in the absence of other AIDS-defining conditions. [1] - At this level, **Pneumocystis pneumonia (PCP)** prophylaxis is typically initiated, but the risk for MAC, while present, is not as high as at lower CD4+ counts. [2] *< 300* - A **CD4+ count below 300 cells/mm3** indicates moderate immunosuppression and an increased risk for various opportunistic infections compared to immunocompetent individuals. - However, it is generally above the threshold for the most severe, late-stage opportunistic infections like MAC.

Q: Cavitary lesions in lung are seen in which of the following infections?

Staphylococcal pneumonia. Staphylococcal pneumonia - Staphylococcus aureus is a common cause of necrotizing pneumonia, which frequently leads to multiple cavitations and abscess formation. - The organism produces toxins that cause extensive tissue destruction, predisposing to cavitary lesions. Primary pulmonary Tuberculosis - Primary TB typically presents as parenchymal consolidation, often in the mid-lung fields, and hilar lymphadenopathy, rather than prominent cavitation. - While cavitation can occur in TB, it is more characteristic of reactivation (secondary) TB, particularly in the lung apices [1]. Klebsiella pneumonia - Klebsiella pneumoniae is known for causing severe, rapidly progressive pneumonia with characteristic bulging interlobar fissures due to voluminous exudate, but cavitation is less common than seen with Staphylococcal infections [2]. - It often leads to lung abscesses and necrosis, but the pattern of cavitation can differ from Staphylococcus aureus or Mycobacterium tuberculosis [3]. Anaerobic lung abscess - Anaerobic infections commonly cause solitary or multiple lung abscesses, which are essentially large cavitary lesions, often due to aspiration. - Although anaerobic lung abscesses result in cavitation, Staphylococcal pneumonia is specifically known for its tendency to produce multiple, widespread cavitations.

Q: An elderly man who had been in several military conflicts during the early 1980s and received blood transfusions for injuries recently consulted his physician for a diagnosis of cryoglobulinemia and glomerulonephritis. Additional testing revealed that he was infected with a virus transmitted through blood. Which virus was involved in this infection?

Hepatitis C Virus (HCV). ***Hepatitis C Virus (HCV)*** - HCV infection is a common cause of **mixed cryoglobulinemia** and can lead to **glomerulonephritis**, particularly membranoproliferative glomerulonephritis. - Before widespread screening of the blood supply, HCV was a significant risk from **blood transfusions**, especially for individuals who received them in the early 1980s [1]. *Hepatitis A Virus (HAV)* - HAV is primarily transmitted via the **fecal-oral route** and does not typically cause chronic infection or lead to cryoglobulinemia or glomerulonephritis. - It causes **acute, self-limiting hepatitis** and is not associated with blood transfusions in the context described. *Hepatitis B Virus (HBV)* - While HBV can be transmitted through blood and can cause glomerulonephritis (e.g., membranous nephropathy), it is less commonly associated with **cryoglobulinemia** in comparison to HCV. - The constellation of cryoglobulinemia and glomerulonephritis, especially with a history of transfusions in the 1980s, points more strongly to HCV. *Hepatitis D Virus (HDV)* - HDV is a **defective virus** that requires co-infection with HBV to replicate. - While it can cause severe liver disease, it is not primarily associated with **cryoglobulinemia** or glomerulonephritis as a direct cause, but rather exacerbates HBV-related complications.

Q: Which of the following is the MOST characteristic clinical feature of Giardiasis?

Diarrhea with foul-smelling stools. ***Diarrhea with foul-smelling stools*** - This is a hallmark symptom of Giardiasis [1], resulting from **malabsorption of fats** due to parasite adherence to the intestinal lining. - The malabsorption leads to **steatorrhea**, characterized by greasy, malodorous, and often floating stools. *Presence of Giardia cysts in stool* - While essential for **diagnosis**, the presence of cysts in stool is a **laboratory finding**, not a clinical feature experienced by the patient. - Clinical features refer to the **symptoms and signs** a patient presents with [1], which are often what prompt diagnostic testing. *Abdominal cramps and bloating* - These are **common symptoms** of Giardiasis, but they are often present in various gastrointestinal disturbances and are **less specific** than foul-smelling diarrhea. - They also can be caused by gas production and intestinal irritation, which frequently accompany many forms of infectious diarrhea. *Nausea and vomiting* - Nausea and vomiting can occur in Giardiasis, but they are **less consistent** and characteristic than the distinctive diarrhea pattern. - These symptoms are **widespread in many gastrointestinal illnesses** and do not specifically point to Giardiasis more than other conditions.

Q: Actinomycosis is most commonly found in which of the following locations?

Mandible. ***Mandible*** - **Cervicofacial actinomycosis** is the most common form, typically manifesting as a chronic, slowly progressing infection in the face and neck, often involving the jaw. - The organism *Actinomyces israelii* is a normal inhabitant of the oral cavity, and infection often occurs after trauma, dental procedures, or poor oral hygiene. *Tibia* - While actinomycosis can affect bone, **direct involvement of long bones** like the tibia is rare and usually occurs via hematogenous spread or direct extension from adjacent soft tissue infections. - It would be an atypical primary or most common presentation for actinomycosis. *Scapula* - Involvement of the scapula is **extremely uncommon** and would typically signify disseminated disease or direct extension from a rare thoracic or cervicofacial presentation. - The scapula is not a common site for localized actinomycosis. *Femur* - Similar to the tibia, **femur involvement** by actinomycosis is rare and usually secondary to other primary sites or widespread disease. - It does not represent a common or typical anatomical location for actinomycosis.

Q: Most common extra-cutaneous manifestation of varicella is involvement of

Lungs. **Lungs** - **Varicella pneumonia** is the most common and serious extra-cutaneous manifestation, particularly in adults, immunocompromised individuals, and pregnant women [1]. - It can lead to severe respiratory distress and has a significant mortality rate. *CNS* - **Aseptic meningitis** and **encephalitis** can occur, but less frequently than pulmonary involvement, and are often mild [1]. - Other neurological complications like **cerebellar ataxia** are also less common than pneumonia. *Kidneys* - **Renal involvement** in varicella is rare and typically mild, such as transient hematuria or proteinuria. - Serious renal complications like acute kidney injury are not characteristic features. *CVS* - **Cardiac complications** like myocarditis or pericarditis are exceedingly rare in varicella infections. - They are not considered a common extra-cutaneous manifestation of the disease.

Q: Which of the following is not a recognized complication of diphtheria?

Vasculitis. ***Vasculitis*** - **Vasculitis** is **not a recognized direct complication** of diphtheria, which primarily involves toxin-mediated damage to tissues [1]. - Diphtheria toxin causes cellular damage leading to inflammation but does not typically induce a systemic vasculitic process [3]. *Polyneuritis* - **Polyneuritis** (also known as diphtheritic polyneuropathy) is a common **neurological complication** of diphtheria, occurring due to the neurotoxic effects of the diphtheria toxin [2]. - It can manifest as **progressive weakness** and *sensory disturbances*, often affecting cranial nerves and eventually peripheral nerves. *Myocarditis* - **Myocarditis** is a serious and potentially fatal **cardiac complication** of diphtheria, resulting from the direct toxic effect of diphtheria toxin on heart muscle cells [2]. - It can lead to **arrhythmias**, **heart failure**, and **cardiogenic shock** [2]. *Palatal paralysis* - **Palatal paralysis** is a **common early neurological complication** of diphtheria, caused by the neurotoxic effects on the nerves supplying the soft palate [2]. - It typically results in **nasal speech** and **regurgitation of fluids** through the nose [2].

Q: Acute endocarditis with abscess is most commonly associated with which organism?

Staphylococcus aureus. ***Staphylococcus aureus*** - **_Staphylococcus aureus_** is the most common cause of **acute infective endocarditis** and is notorious for its rapid destruction of heart valves and its frequent association with **abscess formation** (e.g., peri-annular abscesses, myocardial abscesses). [1] - Its virulence factors, such as hemolysins and coagulase, contribute to its aggressive nature and ability to cause **severe, rapidly progressive disease**. [3] *Listeria* - **_Listeria monocytogenes_** is an uncommon cause of endocarditis, typically seen in immunocompromised individuals or those with prosthetic valves, but it is not the most common organism associated with acute endocarditis and abscess formation. - While it can cause severe systemic infections, **abscess formation** in the context of endocarditis is not its hallmark clinical feature compared to _S. aureus_. *Streptococcus* - **_Streptococcus_ species**, particularly **_Streptococcus viridans_**, are common causes of **subacute infective endocarditis**, often affecting previously damaged valves. [1] - While they can cause complications, they are less frequently associated with **acute onset**, rapid valve destruction, and primary abscess formation compared to _S. aureus_. [2] *Enterococcus* - **_Enterococcus_ species** (e.g., _E. faecalis_, _E. faecium_) are important causes of endocarditis, especially in healthcare-associated infections and in older patients, but are not the leading cause of **acute endocarditis with abscess**. [1] - **Enterococcal endocarditis** tends to be more subacute to chronic in presentation and, while serious, does not commonly feature the aggressive **abscess formation** seen with _S. aureus_.

Q: What is the primary aim of tuberculosis treatment?

Achieving complete bacteriological cure. ***Achieving complete bacteriological cure*** - The primary aim of tuberculosis treatment is to **eliminate all Mycobacterium tuberculosis bacteria** from the patient's body to prevent relapse and further transmission [1]. - This involves a multi-drug regimen administered for a prolonged period to target both actively replicating and dormant bacteria [1]. *Prevention of complications* - While an important aspect of TB management, preventing complications like **pleural effusion** or **meningitis** is a secondary goal that naturally follows effective bacteriological cure [3]. - If the bacteria are not eradicated, **complications can still arise** even if initial symptoms improve. *Prevention of disease spread* - Preventing transmission to others is a crucial public health goal, directly linked to achieving bacteriological cure in the infected individual [1]. - A patient is no longer infectious once **bacteriologically cured**, making this a consequence rather than the primary *aim* of treatment for the individual [1]. *Achieving clinical improvement* - **Symptom resolution** (e.g., fever, cough, weight loss) indicates clinical improvement, but it does not guarantee the eradication of all bacteria. - Patients can feel better with some remaining bacteria, which could lead to **relapse** or **drug resistance** if treatment is stopped prematurely [2].

Q: Cyroglobulinemia is associated with:

Hepatitis C. ***Hepatitis C*** - **Cryoglobulinemia** is most strongly associated with chronic **Hepatitis C virus (HCV)** infection [1]. - HCV infection can lead to the formation of **cryoglobulins**, which are immunoglobulins that precipitate in the cold and can cause systemic vasculitis [1]. *Hepatitis A* - **Hepatitis A** is an acute, self-limiting viral infection that is not typically associated with chronic complications like cryoglobulinemia. - It primarily causes **acute hepatitis** and does not lead to chronic carrier states or immune complex diseases. *Hepatitis B* - While **Hepatitis B virus (HBV)** can be associated with immune complex diseases, such as **polyarteritis nodosa (PAN)** and **glomerulonephritis**, it is less commonly linked to cryoglobulinemia than HCV. - HBV-associated immune complex diseases generally involve different pathogenesis and clinical presentations than HCV-associated cryoglobulinemia. *Hepatitis D* - **Hepatitis D virus (HDV)** infection occurs only in individuals already infected with HBV. - While HDV can worsen the progression of HBV-related liver disease, it is not independently associated with cryoglobulinemia.

Question 1

Mycobacterium avium complex infections are common when the CD4+ counts in cells/mm3 are?

Accepted Answer

< 50

Answer

< 100

Answer

< 200

Answer

< 300

Question 2

Cavitary lesions in lung are seen in which of the following infections?

Accepted Answer

Staphylococcal pneumonia

Answer

Primary pulmonary Tuberculosis

Answer

Klebsiella pneumonia

Answer

Anaerobic lung abscess

Question 3

An elderly man who had been in several military conflicts during the early 1980s and received blood transfusions for injuries recently consulted his physician for a diagnosis of cryoglobulinemia and glomerulonephritis. Additional testing revealed that he was infected with a virus transmitted through blood. Which virus was involved in this infection?

Accepted Answer

Hepatitis C Virus (HCV)

Answer

Hepatitis A Virus (HAV)

Answer

Hepatitis B Virus (HBV)

Answer

Hepatitis D Virus (HDV)

Question 4

Which of the following is the MOST characteristic clinical feature of Giardiasis?

Accepted Answer

Diarrhea with foul-smelling stools

Answer

Presence of Giardia cysts in stool

Answer

Abdominal cramps and bloating

Answer

Nausea and vomiting

Question 5

Actinomycosis is most commonly found in which of the following locations?

Accepted Answer

Mandible

Answer

Tibia

Answer

Scapula

Answer

Femur

Question 6

Most common extra-cutaneous manifestation of varicella is involvement of

Accepted Answer

Lungs

Answer

Kidneys

Answer

CVS

Answer

CNS

Question 7

Which of the following is not a recognized complication of diphtheria?

Accepted Answer

Vasculitis

Answer

Polyneuritis

Answer

Myocarditis

Answer

Palatal paralysis

Question 8

Acute endocarditis with abscess is most commonly associated with which organism?

Accepted Answer

Staphylococcus aureus

Answer

Listeria

Answer

Streptococcus

Answer

Enterococcus

Question 9

What is the primary aim of tuberculosis treatment?

Accepted Answer

Achieving complete bacteriological cure

Answer

Prevention of complications

Answer

Prevention of disease spread

Answer

Achieving clinical improvement

Question 10

Cyroglobulinemia is associated with:

Accepted Answer

Hepatitis C

Answer

Hepatitis A

Answer

Hepatitis B

Answer

Hepatitis D

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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