Infectious Diseases Practice Questions

Q: Which of the following is least appropriate for the treatment of tetanus?

Doxycycline. ***Doxycycline*** - While doxycycline is an antibiotic, it is **not considered a primary agent** for treating tetanus due to its generally inferior efficacy against *Clostridium tetani* compared to other options. - The main goal of antibiotic therapy in tetanus is to **eradicate vegetative forms of C. tetani** at the wound site, to stop further toxin production, which doxycycline is not optimally suited for. *Clindamycin* - **Clindamycin** is an effective antibiotic against *Clostridium tetani* and is often used in combination with metronidazole. - Its mechanism of action involves **inhibiting bacterial protein synthesis**, thereby preventing bacterial growth and toxin production. *Penicillin* - **Penicillin** was historically a first-line antibiotic for tetanus due to its bactericidal activity against *C. tetani*. - However, some concerns exist about its potential to **exacerbate seizures** due to its GABA antagonism, leading to a preference for metronidazole. *Metronidazole* - **Metronidazole** is the antibiotic of choice for tetanus as it is highly effective against anaerobic bacteria like *C. tetani*. - It is preferred over penicillin due to its similar efficacy and **lack of CNS excitability effects**.

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: 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: 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: 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: 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: 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: 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: 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.

Question 1

Which of the following is least appropriate for the treatment of tetanus?

Accepted Answer

Doxycycline

Answer

Clindamycin

Answer

Penicillin

Answer

Metronidazole

Question 2

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 3

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 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

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 6

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 7

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

Accepted Answer

< 50

Answer

< 100

Answer

< 200

Answer

< 300

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

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

Accepted Answer

Vasculitis

Answer

Polyneuritis

Answer

Myocarditis

Answer

Palatal paralysis

Question 10

Most common extra-cutaneous manifestation of varicella is involvement of

Accepted Answer

Lungs

Answer

Kidneys

Answer

CVS

Answer

CNS

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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