Infectious Diseases Practice Questions

Q: Which of the following is not considered an opportunistic infection in AIDS?

Rubella. ***Rubella*** - Rubella, or **German measles**, is a relatively mild viral infection that typically affects children and is not considered an **opportunistic infection** in immunocompromised individuals like those with AIDS [1]. - While it can cause congenital rubella syndrome in infants whose mothers are infected during pregnancy, it does not disproportionately affect or cause severe disease in AIDS patients due to their compromised immunity [1]. *Candidiasis* - **Oropharyngeal** and **esophageal candidiasis** are common opportunistic infections in AIDS patients, often indicating significant immune suppression [2,3]. - The fungus *Candida albicans* can proliferate unchecked when the **CD4 count** is low [2]. *Kaposi's sarcoma* - This is a **cancer** caused by the **human herpesvirus 8 (HHV-8)**, which is a classic AIDS-defining illness [3]. - Its presence indicates severe immunodeficiency and was a hallmark of the early AIDS epidemic [3]. *Cytomegalovirus infection* - **Cytomegalovirus (CMV)** can cause severe and widespread disease in AIDS patients, including **retinitis**, **colitis**, and **encephalitis** [2]. - It becomes a significant risk when the **CD4 count** drops below 100 cells/mm³ [2].

Q: A patient who has developed fever and oral lesions after a trip to Bangkok is diagnosed as:

Enterovirus infection (HFMD). ***Enterovirus infection (HFMD)*** - **Hand, foot, and mouth disease (HFMD)** caused by **enteroviruses** (Coxsackievirus A16, enterovirus 71) classically presents with **fever** and **oral enanthems** (vesicles/ulcers in mouth), often accompanied by vesicular rash on hands and feet. - Travel to **Bangkok/Southeast Asia** is a key epidemiological clue, as this region is **endemic for HFMD**, making it the most likely diagnosis in this clinical context. *Bacterial skin infection* - Bacterial infections typically present with **purulent lesions**, **cellulitis**, or **abscess formation** rather than the characteristic oral vesicles/ulcers described. - The combination of **fever** and **oral lesions** without signs of bacterial involvement (pus, warmth, erythema) makes this diagnosis less likely. *Viral skin infection* - While **herpes simplex virus** can cause oral lesions, the travel history to Bangkok specifically points to **HFMD** as the intended diagnosis rather than HSV. - Other viral skin infections like **varicella** or **measles** have distinct rash patterns that differ from the oral-predominant presentation described. *Autoimmune blistering disorder* - Conditions like **pemphigus vulgaris** or **bullous pemphigoid** typically present as chronic blistering diseases without acute **fever** or travel-related onset. - These disorders are **non-infectious** and usually affect older patients with gradual onset, unlike the acute febrile presentation following recent travel.

Q: In a patient where only Anti-HBsAg is positive in the serum, with all other viral markers being negative, this indicates

Immunized person with hepatitis B vaccine. ***Immunized person with hepatitis B vaccine*** - The presence of **Anti-HBsAg** (Hepatitis B surface antibody) as the *only* positive marker indicates immunity to hepatitis B [1]. - This immunity is most commonly acquired through **vaccination**, which introduces HBsAg to the immune system, leading to anti-HBsAg production without actual infection [1]. *Acute hepatitis infection* - Acute hepatitis B infection would typically show positive **HBsAg** (Hepatitis B surface antigen) and **Anti-HBc IgM** (hepatitis B core antibody, IgM class) [1]. - Anti-HBsAg is generally *not* present during acute infection, as it signals resolution or immunity rather than active disease [1]. *Chronic hepatitis infection* - A chronic hepatitis B infection would involve persistent **HBsAg** positivity for more than six months, often accompanied by **Anti-HBc IgG** and sometimes **HBeAg** [1]. - The isolated presence of Anti-HBsAg rules out chronic infection [1]. *Chronic carrier state* - A chronic carrier state is characterized by persistent presence of **HBsAg** in the blood, indicating ongoing viral replication or presence [1]. - The absence of HBsAg and the sole presence of anti-HBsAg would contradict a chronic carrier state [1].

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: 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: 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: 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: Duration of treatment in paucibacillary leprosy is?

6 months. ***6 months*** [1] - The World Health Organization (WHO) recommends a **6-month multidrug therapy (MDT)** regimen for paucibacillary (PB) leprosy [1]. - This regimen typically includes **rifampicin** and **dapsone** [1]. *9 months* - This duration is **not the standard WHO recommendation** for paucibacillary leprosy. - Longer durations (e.g., 12 months) are typically reserved for multibacillary leprosy [1]. *2 years* - A 2-year treatment duration is **excessive** for paucibacillary leprosy. - This longer period is usually associated with **multibacillary leprosy** [1] or specific relapse cases. *Till symptoms subside* - Treatment for leprosy is based on a **fixed-duration regimen**, not on symptom resolution [1]. - Stopping treatment once symptoms subside can lead to **relapse** and drug resistance.

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: Which of the following waterborne diseases is characterized by rice water stools?

Cholera. ***Typhoid fever*** - **Rice water stools** are a classic symptom of **cholera**, not typhoid fever. Typhoid fever is characterized by a **step-ladder fever pattern**, **bradycardia**, and abdominal pain, eventually leading to a rose-spot rash. - The causative agent of typhoid fever is **Salmonella typhi**, which primarily invades the gastrointestinal tract and then disseminates systemically. *Giardiasis* - Giardiasis is caused by the parasite **Giardia lamblia**, and its typical symptoms include **fatty**, **foul-smelling stools**, **bloating**, cramps, and weight loss, not rice water stools. - This infection is often acquired through the ingestion of **cysts** from contaminated water or food. *Cholera* - **Cholera** is the correct answer and is classically characterized by the production of **massive watery diarrhea** with **“rice water” stools**, which are gray, turbid, and flecked with mucus. - This severe dehydration is due to the action of **cholera toxin**, which causes electrolyte and fluid secretion into the intestinal lumen. *Hepatitis A* - **Hepatitis A** is primarily a **viral liver infection** characterized by **jaundice**, dark urine, fatigue, and nausea, and it does not typically present with diarrhea, especially not rice water stools. - It is transmitted via the **fecal-oral route**, often through contaminated food or water, but its primary target is the liver.

Question 1

Which of the following is not considered an opportunistic infection in AIDS?

Accepted Answer

Rubella

Answer

Candidiasis

Answer

Kaposi's sarcoma

Answer

Cytomegalovirus infection

Question 2

A patient who has developed fever and oral lesions after a trip to Bangkok is diagnosed as:

Accepted Answer

Enterovirus infection (HFMD)

Answer

Bacterial skin infection

Answer

Viral skin infection

Answer

Autoimmune blistering disorder

Question 3

In a patient where only Anti-HBsAg is positive in the serum, with all other viral markers being negative, this indicates

Accepted Answer

Immunized person with hepatitis B vaccine

Answer

Acute hepatitis infection

Answer

Chronic hepatitis infection

Answer

Chronic carrier state

Question 4

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 5

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

Accepted Answer

< 50

Answer

< 100

Answer

< 200

Answer

< 300

Question 6

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 7

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 8

Duration of treatment in paucibacillary leprosy is?

Accepted Answer

6 months

Answer

9 months

Answer

2 years

Answer

Till symptoms subside

Question 9

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

Accepted Answer

Staphylococcus aureus

Answer

Listeria

Answer

Streptococcus

Answer

Enterococcus

Question 10

Which of the following waterborne diseases is characterized by rice water stools?

Accepted Answer

Cholera

Answer

Giardiasis

Answer

Typhoid fever

Answer

Hepatitis A

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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