Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 111: Which of the following is not a mode of transmission for Hepatitis B?

A. Transmission occurs via sexual contact
B. Transmitted by respiratory droplets (Correct Answer)
C. Can be transmitted from mother to child
D. Transmission occurs via blood

Explanation: ***Transmitted by respiratory droplets*** - Hepatitis B virus (HBV) is primarily transmitted through bodily fluids, not through the air via **respiratory droplets** like cold or flu viruses. - This means casual contact, coughing, or sneezing does **not** spread HBV. *Transmission occurs via sexual contact* - HBV is highly concentrated in bodily fluids like **blood, semen, and vaginal secretions**, making sexual intercourse a common mode of transmission. - Unprotected sexual contact with an infected partner significantly increases the risk of acquiring HBV. *Can be transmitted from mother to child* - **Perinatal transmission** from an infected mother to her baby during birth is a significant route of HBV transmission, especially in endemic areas. - This can lead to chronic infection in infants if not prevented with vaccination and hepatitis B immunoglobulin. *Transmission occurs via blood* - HBV is readily transmitted through contact with infected blood, such as via **sharing needles** among intravenous drug users or through **blood transfusions** in settings where screening is inadequate. - Accidental **needle sticks** in healthcare settings are also a risk factor for HBV transmission.

Question 112: A 30-year-old woman with a history of HIV presents with a persistent fever and night sweats. Blood cultures reveal non-lactose fermenting gram-negative rods. Which pathogen is most likely?

A. Klebsiella pneumoniae
B. Salmonella typhi (Correct Answer)
C. Escherichia coli
D. Enterobacter cloacae

Explanation: ***Salmonella typhi*** - **Salmonella typhi** is a **non-lactose fermenting gram-negative rod** commonly associated with **persistent fever**, **night sweats**, and **bacteremia**, especially in immunocompromised individuals like those with HIV. - It causes **typhoid fever**, a systemic illness characterized by prolonged fever, **rose spots**, and hepatosplenomegaly. - **Note:** In HIV patients, non-typhoidal Salmonella species (e.g., *S. enteritidis*, *S. typhimurium*) are actually more common causes of recurrent bacteremia, but *S. typhi* remains a significant pathogen and is the only non-lactose fermenter among the given options. *Escherichia coli* - **Escherichia coli** is typically a **lactose-fermenting gram-negative rod**, which contradicts the blood culture finding of a non-lactose fermenter. - While *E. coli* can cause fever and bacteremia, it usually presents as a more acute infection, such as a **urinary tract infection (UTI)** or **sepsis**, rather than prolonged fever and night sweats in this context. *Klebsiella pneumoniae* - **Klebsiella pneumoniae** is a **lactose-fermenting gram-negative rod**, inconsistent with the blood culture result. - It commonly causes **pneumonia** and UTIs, and while it can lead to bacteremia, the fermentation characteristic excludes it in this scenario. *Enterobacter cloacae* - **Enterobacter cloacae** is a **lactose-fermenting gram-negative rod**, making it unlikely given the non-lactose fermenting finding. - It is often associated with nosocomial infections and can cause bacteremia, but the lactose fermentation characteristic is key in differentiation here.

Question 113: Which pathogen is commonly responsible for causing diarrhea in patients with HIV/AIDS?

A. Cryptosporidium (Correct Answer)
B. Giardia lamblia
C. Escherichia coli
D. Clostridium difficile

Explanation: ***Cryptosporidium*** - **Cryptosporidium** is the most common opportunistic pathogen causing diarrhea in HIV/AIDS patients, especially those with CD4 counts <200 cells/μL - Causes **chronic, severe, watery diarrhea** that can be life-threatening in immunocompromised individuals - The parasite's ability to cause disease is amplified due to impaired cell-mediated immunity, resulting in **prolonged infection** and malabsorption - Cryptosporidiosis is an AIDS-defining opportunistic infection *Giardia lamblia* - While **Giardia lamblia** causes diarrhea (giardiasis), it is not typically an opportunistic infection specific to HIV/AIDS - Affects both immunocompetent and immunocompromised individuals equally - Symptoms include **greasy, foul-smelling stools** and **abdominal cramps**, but rarely causes the severe, chronic wasting diarrhea seen with cryptosporidiosis in AIDS *Escherichia coli* - Various strains of **E. coli** can cause diarrhea in both immunocompetent and immunocompromised individuals - Not uniquely associated with severe, chronic diarrhea in HIV/AIDS as an opportunistic pathogen - Can cause traveler's diarrhea or food poisoning, but typically doesn't lead to the severe wasting syndrome characteristic of AIDS-related opportunistic infections *Clostridium difficile* - **C. difficile** infection is primarily associated with **antibiotic use** disrupting the gut microbiota, leading to pseudomembranous colitis - While HIV-positive individuals can develop C. difficile infection, it's not an AIDS-defining opportunistic infection - Related to antibiotic exposure rather than HIV-induced immunosuppression directly

Question 114: What is the cause of Ritter disease?

A. Staphylococcus aureus infection (Correct Answer)
B. Autoimmune disease
C. Genetic disorder
D. Metabolic disorder

Explanation: ***Staphylococcus aureus infection*** - **Ritter disease**, also known as **Staphylococcal Scalded Skin Syndrome (SSSS)**, is caused by specific strains of **Staphylococcus aureus** that produce exfoliative toxins (ETA and ETB). - These toxins target **desmoglein 1**, a protein responsible for cell-to-cell adhesion in the stratum granulosum of the epidermis, leading to widespread blistering and skin shedding. *Autoimmune disease* - Autoimmune diseases involve the immune system mistakenly attacking the body's own tissues, as seen in conditions like **pemphigus vulgaris** or **bullous pemphigoid**. - Ritter disease is caused by an **exotoxin produced by bacteria**, not an immune response against self-antigens. *Genetic disorder* - Genetic disorders result from mutations or abnormalities in an individual's **DNA**, leading to functional or structural defects. - While susceptibility to infections can have genetic components, Ritter disease itself is directly caused by an **external bacterial infection**, not an inherited genetic defect. *Metabolic disorder* - Metabolic disorders occur when the body's normal chemical reactions are disrupted, often due to enzyme deficiencies or abnormal accumulation of substances, such as in **phenylketonuria** or **Tay-Sachs disease**. - Ritter disease is an **infectious condition** with a distinct bacterial etiology, not a problem with metabolism.

Question 115: A patient operated for transurethral resection of prostate [TURP] develops UTI. The organism most commonly grown on culture will be -

A. Proteus
B. E. coli (Correct Answer)
C. Pseudomonas
D. Klebsiella

Explanation: ***E. coli*** - **_E. coli_** is the most common pathogen responsible for both **community-acquired** and **healthcare-associated urinary tract infections (UTIs)**, including those following surgical procedures like TURP. - It accounts for **50-70% of healthcare-associated UTIs** and has enhanced ability to adhere to urothelial cells and form biofilms. - Its virulence factors make it the predominant uropathogen in post-operative settings. *Proteus* - While **_Proteus mirabilis_** can cause UTIs, particularly those associated with **struvite stones** due to urease production, it is not as common as _E. coli_ in post-TURP UTIs. - It accounts for approximately **5-10% of healthcare-associated UTIs** and often causes **alkaline urine** with characteristic "swarming" growth on culture. *Pseudomonas* - **_Pseudomonas aeruginosa_** is an important cause of **healthcare-associated UTIs**, especially in catheterized patients or those with complicated infections. - However, it accounts for only **10-15% of nosocomial UTIs** and is less common than _E. coli_ unless there are specific risk factors such as prolonged catheterization or previous antibiotic exposure. *Klebsiella* - **_Klebsiella pneumoniae_** is the **second most common cause of UTIs** after _E. coli_, accounting for **10-15% of cases**. - It is particularly associated with **healthcare settings**, catheter-related infections, and patients with diabetes or immunosuppression. - While important, it is still less common than _E. coli_ in post-TURP UTIs.

Question 116: What is the primary method for diagnosing Pneumocystis jirovecii pneumonia?

A. Sputum microscopy
B. Chest X-ray findings
C. Bronchoalveolar lavage (BAL) (Correct Answer)
D. Serum beta-D-glucan assay

Explanation: ***Bronchoalveolar lavage (BAL)*** - **BAL** is the **gold standard** and **primary definitive method** for diagnosing *Pneumocystis jirovecii* pneumonia (PJP), with **sensitivity of 90-99%** and high specificity. - It involves bronchoscopy with lavage of the affected lung segments, allowing direct visualization and sampling of organisms using stains like **Gomori methenamine silver (GMS)**, **Giemsa**, or **immunofluorescence**. - BAL is particularly important in **immunocompromised patients** (HIV/AIDS, transplant recipients, chemotherapy patients) where definitive diagnosis is crucial for treatment decisions. - Though invasive, it remains the **most reliable diagnostic method** when PJP is suspected, especially when non-invasive methods are negative or inconclusive. *Sputum microscopy* - **Induced sputum microscopy** is a useful **initial non-invasive screening method**, but has **limited sensitivity (50-60%)** compared to BAL. - Many PJP patients cannot produce adequate sputum samples, and negative results do not exclude the diagnosis. - When positive, it can guide early treatment, but **negative sputum requires proceeding to BAL** for definitive diagnosis in high-suspicion cases. *Serum beta-D-glucan assay* - The **serum beta-D-glucan assay** is a **highly sensitive supportive marker** for PJP (sensitivity 90-95%), detecting fungal cell wall components. - However, it is an **indirect test** that cannot differentiate PJP from other fungal infections (*Candida*, *Aspergillus*). - Used as an **adjunctive diagnostic tool** rather than a primary definitive method, particularly helpful in risk stratification. *Chest X-ray findings* - **Chest X-ray** typically shows **bilateral interstitial infiltrates** in a "ground-glass" pattern, but findings are **non-specific** and can be normal in early disease. - Radiographic findings support clinical suspicion but **cannot provide definitive diagnosis** without microbiological confirmation. - Useful for initial assessment and monitoring treatment response, not for primary diagnosis.

Question 117: What is the mammalian reservoir for Rickettsia prowazekii?

A. Rodents
B. Dogs
C. Cattle
D. Humans (Correct Answer)

Explanation: ***Humans*** - **Humans** are the primary and essentially sole mammalian reservoir for *Rickettsia prowazekii*, the causative agent of **epidemic typhus** - This characteristic makes **epidemic typhus** a human-to-human disease, primarily transmitted via the **human body louse** (*Pediculus humanus corporis*) - The disease can persist in human populations and reactivate years later as **Brill-Zinsser disease** (recrudescent typhus) *Rodents* - Rodents are reservoirs for other *Rickettsia* species, such as *Rickettsia typhi* (cause of **murine typhus**), but not for *Rickettsia prowazekii* - **Murine typhus** is typically transmitted by the **rat flea**, distinguishing its epidemiology from that of epidemic typhus *Dogs* - Dogs are known reservoirs for various disease-causing agents, including some rickettsial diseases like **Rocky Mountain spotted fever** (*Rickettsia rickettsii*), but not for *Rickettsia prowazekii* - Different *Rickettsia* species have specific **animal hosts** and **arthropod vectors** *Cattle* - Cattle are not typically considered a reservoir for *Rickettsia prowazekii* - They are more commonly associated with diseases like **Q fever** (*Coxiella burnetii*), which is related but distinct from typhus rickettsiae

Question 118: Which of the following viruses does not typically cause viral hepatitis?

A. Measles
B. EBV
C. Rhinovirus (Correct Answer)
D. Reovirus

Explanation: ***Rhinovirus*** - **Rhinoviruses** are the primary cause of the common cold, affecting the **upper respiratory tract**, and are not known to typically cause hepatitis. - They replicate optimally at lower temperatures found in the nasal passages, rather than the higher temperatures of internal organs like the liver. *Measles* - The **measles virus** (rubeola) can cause **transaminitis** and, in rare severe cases, can lead to hepatitis as part of a systemic infection. - While not its primary target, liver inflammation can occur in connection with measles. *EBV* - **Epstein-Barr virus (EBV)** is a common cause of **infectious mononucleosis** and frequently causes **mild, self-limiting hepatitis**, characterized by elevated liver enzymes. - In some cases, EBV can lead to more significant or prolonged hepatitis, especially in immunocompromised individuals. *Reovirus* - **Reoviruses** can cause a range of infections, including **gastroenteritis** and respiratory illnesses, and are known to cause hepatitis in infants and immunocompromised individuals. - While not as common as other hepatitis viruses, reoviruses can lead to liver inflammation.

Question 119: LGV (lymphogranuloma venereum) is caused by?

A. Chlamydia trachomatis (Correct Answer)
B. Calymmatobacter granulomatis
C. Haemophilus ducreyi
D. Treponema pallidum

Explanation: ***Correct: Chlamydia trachomatis*** - **Lymphogranuloma venereum (LGV)** is a sexually transmitted infection caused by specific serovars (**L1, L2, L3**) of *Chlamydia trachomatis* - These serovars are **invasive** and replicate in **mononuclear phagocytes** in regional lymph nodes - LGV presents with **painless genital ulcer** followed by **painful inguinal lymphadenopathy** (buboes) *Incorrect: Calymmatobacter granulomatis* - This bacterium causes **granuloma inguinale** (donovanosis), not LGV - Characterized by **painless, progressive ulcerative lesions** without prominent lymphadenopathy - Diagnosis shows **Donovan bodies** on tissue smear *Incorrect: Haemophilus ducreyi* - *H. ducreyi* causes **chancroid**, not LGV - Presents with **painful genital ulcers** and **suppurative inguinal lymphadenitis** - Key difference: painful ulcers (vs painless in LGV primary lesion) *Incorrect: Treponema pallidum* - *T. pallidum* causes **syphilis**, not LGV - Primary syphilis presents with **painless chancre** with firm borders - Lymphadenopathy is bilateral, firm, and non-tender (different from LGV buboes)

Question 120: Which of the following organisms is least likely to cause urethritis?

A. Chlamydia
B. Gonococcus
C. Trichomonas
D. H.ducreyi (Correct Answer)

Explanation: ***Haemophilus ducreyi*** - *Haemophilus ducreyi* is the causative agent of **chancroid**, an STI characterized by **painful genital ulcers** and regional lymphadenopathy. - While it's an STI, its primary manifestation is **not urethritis** but rather ulcerative disease. - Therefore, it is the **least likely** among these options to cause urethritis. *Trichomonas vaginalis* - *Trichomonas vaginalis* is a common cause of **trichomoniasis**, which can manifest as urethritis in both men and women. - In men, it can cause **non-gonococcal urethritis (NGU)** with symptoms like dysuria and penile discharge. *Chlamydia trachomatis* - *Chlamydia trachomatis* is one of the most frequent causes of **non-gonococcal urethritis (NGU)**. - It is the **leading cause of NGU** and often leads to **asymptomatic urethritis**, but can also cause dysuria and discharge. *Neisseria gonorrhoeae* - *Neisseria gonorrhoeae* (gonococcus) is a classic cause of **gonococcal urethritis**. - It typically results in **purulent urethral discharge** and painful urination.

Practice by Chapter

Respiratory Tract Infections

Practice Questions

Urinary Tract Infections

Practice Questions

Gastrointestinal Infections

Practice Questions

Skin and Soft Tissue Infections

Practice Questions

Central Nervous System Infections

Practice Questions

Bone and Joint Infections

Practice Questions

Cardiovascular Infections

Practice Questions

Sexually Transmitted Infections

Practice Questions

Zoonotic Infections

Practice Questions

Bloodstream Infections and Sepsis

Practice Questions

Fever of Unknown Origin

Practice Questions

Infections in Immunocompromised Host

Practice Questions

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