Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 801: Most common opportunistic infection in AIDS worldwide is:-

A. Candida
B. Histoplasmosis
C. Tuberculosis
D. Pneumocystis jirovecii pneumonia (Correct Answer)

Explanation: ***Pneumocystis jirovecii pneumonia*** - Historically and currently, **Pneumocystis jirovecii pneumonia (PJP)** is the most common serious opportunistic infection in patients with **AIDS** in resource-rich settings [1]. - It presents with **non-productive cough**, **dyspnea**, and **fever**, with a characteristic diffuse interstitial infiltrate on chest X-ray. *Candida* - **Oropharyngeal candidiasis (thrush)** is very common in AIDS patients, but it is generally a milder infection and not typically considered the "most common opportunistic infection" in terms of severity and mortality on a global scale. - While it can be a sign of immunosuppression, disseminated **candidiasis** is less frequent than PJP or TB [1]. *Histoplasmosis* - **Histoplasmosis** is an opportunistic fungal infection primarily found in specific geographic regions where the fungus is endemic (e.g., Ohio and Mississippi River valleys in the US) [1]. - It is not the most common opportunistic infection worldwide, as its prevalence is limited by geographical factors. *Tuberculosis* - **Tuberculosis (TB)** is the leading cause of death among people with **HIV/AIDS** worldwide, particularly in resource-limited settings [1]. - While extremely prevalent and deadly, PJP generally surpassed TB as the most common *initial* opportunistic infection in the early stages of the AIDS epidemic in many regions, and its incidence remains high globally, especially as a presenting illness of **AIDS**.

Question 802: A 40-year old woman presented to the surgical OPD with features suggestive of colitis. She was on prolonged treatment with clindamycin. Fecal sample was positive for toxin produced by this agent. Her condition improved on treatment with metronidazole. The clinical condition is associated with -

A. Listeria monocytogenes
B. Bacillus anthracis
C. Clostridium difficile (Correct Answer)
D. Acinetobacter baumannii

Explanation: ***Clostridium difficile*** - The history of **clindamycin use**, followed by **colitis symptoms**, a **positive fecal toxin test**, and improvement with **metronidazole**, are classic indicators of *Clostridium difficile* infection (CDI) [1]. - *C. difficile* produces toxins (Toxin A and Toxin B) that cause **pseudomembranous colitis**, often after antibiotic disruption of normal gut flora [1]. *Listeria monocytogenes* - This bacterium is primarily a cause of **foodborne illness**, leading to febrile gastroenteritis, meningitis, or sepsis, particularly in immunocompromised individuals, pregnant women, and neonates. - It is not typically associated with **antibiotic-associated colitis** or treated with metronidazole as a primary agent for bowel infection. *Bacillus anthracis* - This is the causative agent of **anthrax**, which can manifest as cutaneous, inhalational, or gastrointestinal forms. - **Gastrointestinal anthrax** causes severe abdominal pain, vomiting, bloody diarrhea, and fever, but it is rare and not linked to antibiotic use or toxin detection in stool in the context described. *Acinetobacter baumannii* - *Acinetobacter baumannii* is an important **opportunistic pathogen** often associated with hospital-acquired infections, such as pneumonia, urinary tract infections, and bloodstream infections, particularly in critically ill patients. - It is not a known cause of **antibiotic-associated colitis** due to toxin production, nor is metronidazole the primary treatment.

Question 803: Most characteristic oral lesion associated with HIV is:

A. Herpes simplex
B. Gingivitis
C. Oral hairy leukoplakia (Correct Answer)
D. Aphthous ulcers

Explanation: ***Oral hairy leukoplakia*** - This lesion is a **white, corrugated patch** that typically appears on the lateral borders of the tongue and cannot be scraped off. - It is caused by the **Epstein-Barr virus (EBV)** and is a strong indicator of **HIV progression** to AIDS, especially in individuals with declining CD4 counts. *Herpes simplex* - While common in HIV-positive individuals, **herpes simplex** presents as painful vesicles and ulcers, often recurrent, and is not exclusive to HIV [2]. - Oral hairy leukoplakia is far more specific and characteristic as an **early indicator** of HIV-related immune suppression. *Gingivitis* - **Gingivitis** is widespread inflammation of the gums and is very common in the general population, not specifically characteristic of HIV infection solely [1]. - Although more severe forms like **necrotizing ulcerative gingivitis** can be seen in advanced HIV, simple gingivitis is not the most characteristic oral lesion [1]. *Aphthous ulcers* - **Aphthous ulcers** are common, painful, recurrent oral lesions that can occur in the general population and are not specific to HIV [3]. [4] - While they can be more severe and persistent in HIV-positive individuals, they lack the diagnostic specificity seen with oral hairy leukoplakia [1].

Question 804: A man presents with fever and chills 2 weeks after a louse bite. There was maculo-papular rash on the trunk which spread peripherally. The cause of this infection can be -

A. Endemic typhus
B. Rickettsial pox
C. Epidemic typhus (Correct Answer)
D. Scrub typhus

Explanation: ***Epidemic typhus*** - **Epidemic typhus** is caused by **Rickettsia prowazekii** and transmitted by the **human body louse (Pediculus humanus corporis)**, consistent with the history of a louse bite. - The classic presentation includes **fever, chills**, and a **maculopapular rash** that starts on the trunk and spreads centrifugally, sparing the palms and soles [1]. *Endemic typhus* - **Endemic typhus** (murine typhus) is caused by **Rickettsia typhi** and transmitted by the **rat flea**, not a louse [1]. - While it also presents with fever and rash, the distinct vector and, typically, milder course differentiate it from epidemic typhus. *Rickettsial pox* - **Rickettsialpox** is caused by **Rickettsia akari** and transmitted by the **mite** from house mice, not a louse. - It is characterized by an **eschar** at the bite site followed by a generalized papulovesicular rash, which is different from the maculopapular rash described. *Scrub typhus* - **Scrub typhus** is caused by **Orientia tsutsugamushi** and transmitted by the **chigger mite** larvae, not a louse [1]. - Similar to rickettsialpox, it typically presents with an **eschar** at the bite site and can cause generalized rash, but the vector is different [1].

Question 805: Most common site of tuberculosis in gastrointestinal tract is ?

A. Small intestine
B. Stomach
C. Rectum
D. Ileocecal junction (Correct Answer)

Explanation: ***Ileocecal junction*** - The **ileocecal junction** is the most common site for gastrointestinal tuberculosis due to its rich lymphatic tissue, physiological stasis, and abundant fluid absorption. - The presence of Peyer's patches and constant exposure to luminal contents make it susceptible to colonization and granuloma formation by *Mycobacterium tuberculosis*. *Small intestine* - While the small intestine can be affected by tuberculosis, the **ileocecal junction** specifically is the predominant site within the small intestine and overall GI tract. - Other parts of the small intestine, such as the jejunum and duodenum, are less commonly involved due to faster transit time and fewer lymphoid follicles. *Stomach* - The **stomach** is rarely affected by tuberculosis due to its highly acidic environment, which is inhibitory to mycobacterial growth. - Gastric involvement, when it occurs, usually presents as ulcers or pyloric obstruction, but it is not the most common site. *Rectum* - The **rectum** is an uncommon site for gastrointestinal tuberculosis; when involved, it often presents with strictures or ulcers. - Rectal tuberculosis is typically seen in patients with disseminated disease or in immunocompromised individuals.

Question 806: Reactivation tuberculosis is almost exclusively a disease of the -

A. Joints
B. Brain
C. Lungs (Correct Answer)
D. Bones

Explanation: Lungs - Reactivation tuberculosis (TB) predominantly affects the lungs, presenting as secondary pulmonary TB [1]. - It arises from the reactivation of dormant Mycobacterium tuberculosis bacteria in the lungs, often decades after primary infection [3]. Joints - While TB can affect joints (known as Pott's disease when it affects the spine), it is a less common manifestation than pulmonary involvement, particularly in reactivation [2]. - Joint involvement typically occurs via hematogenous spread from a primary pulmonary focus [2]. Brain - Tuberculosis of the brain, or tuberculous meningitis, is a severe but less common extrapulmonary form of TB [2]. - It usually results from the rupture of a subpial or subependymal tubercle into the subarachnoid space. Bones - Bone TB is another form of extrapulmonary tuberculosis, often involving the spine [2]. - Like joint involvement, it is less frequently seen compared to the almost exclusive pulmonary involvement in reactivation.

Question 807: In HIV patients, Kaposi's sarcoma is most likely caused by which of the following?

A. Bacteria
B. Parasite
C. Fungus
D. Virus (Correct Answer)

Explanation: ***Virus*** - The image likely depicts **Kaposi's sarcoma**, a common lesion in HIV patients, which is caused by **Human Herpesvirus 8 (HHV-8)**. - Other viral infections like **Herpes Simplex Virus (HSV)** can also cause mucocutaneous lesions in immunocompromised individuals. *Bacteria* - While HIV patients are susceptible to bacterial infections (e.g., **Staphylococcus aureus** causing skin abscesses), the described lesion type is not characteristic of common bacterial skin infections. - Bacterial lesions often present as pustules, cellulitis, or ulcers with purulent discharge, which differ from typical Kaposi's sarcoma. *Parasite* - Parasitic infections can occur in HIV patients (e.g., **scabies** or **leishmaniasis**), but these typically present with different dermatological features like intensely itchy papules or nodular ulcerative lesions. - Lesions caused by parasites do not usually manifest as the violaceous, nodular, or plaque-like appearances seen in Kaposi's sarcoma. *Fungus* - Fungal infections in HIV patients can cause skin lesions (e.g., **candidiasis** with oral thrush or esophagitis, or **cryptococcosis** with molluscum-like lesions). - However, the morphology of these fungal lesions generally differs from the classic appearance of Kaposi's sarcoma or other common viral lesions in HIV.

Question 808: Which of the following is NOT a characteristic of hepatitis B infection?

A. HBcAg in serum indicate active infection (Correct Answer)
B. Alpha interferon is used for the treatment of chronic infection
C. Establishes chronic infections in those infected as infants
D. Can cause hepatocellular carcinoma

Explanation: Hepatitis B core antigen (HBcAg) is found within the infected hepatocytes and is not secreted into the bloodstream [1]. The presence of HBcAg in serum would typically indicate a ruptured hepatocyte and damaged liver, but it is not a routine marker for active infection. Alpha interferon is a common antiviral medication used in the treatment of chronic hepatitis B infection [1]. Its mechanism of action involves modulating the immune system to clear the virus and prevent liver damage. Perinatal transmission of hepatitis B is a major route, and infants infected at birth have a high risk (up to 90%) of developing chronic hepatitis B [1]. Their immature immune systems often fail to clear the virus, leading to persistent infection. Chronic hepatitis B infection is a significant risk factor for developing hepatocellular carcinoma (HCC) [1]. The persistent inflammation and liver damage associated with chronic infection promote cellular dysplasia and malignant transformation.

Question 809: Following urinary tract infection associated with extraction of a bladder stone, a 64-year-old woman developed gram-negative septicemia. Which statement is true for gram-negative bacterial septicemia?

A. Many of the adverse changes can be accounted for endotoxin release. (Correct Answer)
B. Pseudomonas is the most common organism isolated.
C. Central venous pressure (CVP) is high.
D. The cardiac index is low.

Explanation: ***Many of the adverse changes can be accounted for endotoxin release.*** - Gram-negative bacteria contain **lipopolysaccharide (LPS)** in their outer membrane, which acts as an **endotoxin**. - During infection and bacterial lysis, **LPS** is released, triggering a severe inflammatory response leading to **septic shock**, **coagulopathy**, and **organ dysfunction**. *Pseudomonas is the most common organism isolated.* - While *Pseudomonas aeruginosa* can cause severe infections, **Escherichia coli** is the most common gram-negative bacterium isolated in cases of **septicemia** originating from the urinary tract [1]. - Other common culprits include **Klebsiella pneumoniae** and **Proteus mirabilis**. *Central venous pressure (CVP) is high.* - In **septic shock**, patients typically exhibit **vasodilation** and **capillary leak**, leading to **hypovolemia** and a **low CVP**, indicating reduced preload. - A high CVP would suggest fluid overload or right heart failure, which is not typical in the initial stages of gram-negative septicemia. *The cardiac index is low.* - **Septic shock** is characterized by an initial phase of **hyperdynamic circulation**, where the **cardiac index** is often **high** due to decreased systemic vascular resistance and increased cardiac output striving to maintain perfusion. - While prolonged or severe shock can eventually lead to myocardial depression and a reduced cardiac index, the initial response is typically hyperdynamic.

Question 810: Most sensitive test for diagnosis of infectious mononucleosis:

A. Monospot test
B. Culture of the virus
C. Lymphocytosis in peripheral smear
D. Paul Bunnel test (Correct Answer)

Explanation: ***Paul Bunnel test*** - The **Paul-Bunnell test** detects heterophile antibodies by agglutinating sheep red blood cells, which are characteristic of infectious mononucleosis. - While largely replaced by the **Monospot test**, it is historically known for its **sensitivity** in detecting these antibodies. *Monospot test* - The **Monospot test** is a rapid, widely used test for infectious mononucleosis that detects **heterophile antibodies**, but its sensitivity is lower in the early stages of the disease. - Although convenient, it can produce **false negatives**, especially in young children or very early in the infection. *Culture of the virus* - **Culturing Epstein-Barr virus (EBV)**, the causative agent of infectious mononucleosis, is **not practical for routine diagnosis** due to its technical complexity and long turnaround time [1]. - Viral culture is typically reserved for **research purposes** rather than clinical diagnosis [1]. *Lymphocytosis in peripheral smear* - While **atypical lymphocytosis** (more than 10% atypical lymphocytes) on a peripheral smear is a **characteristic finding** in infectious mononucleosis, it is **not specific** for the condition [1]. - This finding can also be present in other viral infections and does not confirm the diagnosis on its own; it serves as a **supportive indicator** [1].

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

Practice Questions

HIV/AIDS and Related Infections

Practice Questions

Tuberculosis and Mycobacterial Diseases

Practice Questions

Tropical and Parasitic Infections

Practice Questions

Viral Infections (Hepatitis, Herpes, etc.)

Practice Questions

Healthcare-Associated Infections

Practice Questions

Fungal Infections

Practice Questions

Sepsis and Septic Shock

Practice Questions

Infection in Immunocompromised Hosts

Practice Questions

Emerging and Re-emerging Infections

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Antimicrobial Resistance

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Vaccination Principles

Practice Questions

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