Infectious Diseases — MCQs

A patient presents to the emergency room with vomiting, diarrhea, high fever, and delirium. Upon physical examination, you notice large buboes, which are painful on palpation, and purpura and ecchymoses suggestive of disseminated intravascular coagulation. Gram stain on aspirate of a bubo reveals gram-negative rods with bipolar staining. Which of the following antibiotics is the drug of choice for empiric therapy?

Q928

Legionella causes:

Q929

A man with chills, fever, and headache is thought to have "atypical" pneumonia. History reveals that he raises chickens, and that approximately 2 weeks ago he lost a large number of them to an undiagnosed disease. Which of the following is the most likely diagnosis of this man's condition?

Q930

Regarding yaws, all are true except -

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 921: Which of the following statements is true about dengue fever? a) ↑ Hematocrit b) ↓ Platelet c) Positive tourniquet test d) Vector (Aedes aegypti) usually bites in day time

A. ↑ Hematocrit
B. ↓ Platelet
C. Positive tourniquet test
D. Vector (Aedes aegypti) usually bites in day time (Correct Answer)

Explanation: ***Vector (Aedes aegypti) usually bites in day time*** - The **Aedes aegypti mosquito**, the primary vector for dengue, is a **day-biting** mosquito, particularly active during early morning and late afternoon. - This characteristic behavior influences prevention strategies, as protection is needed during daylight hours. *↑ Hematocrit* - An **increased hematocrit** is a sign of **plasma leakage** and **hemoconcentration**, which is a *potential complication* of severe dengue [1]. - While it can occur, it's not a universal feature of all dengue cases and is more indicative of **dengue hemorrhagic fever** or **dengue shock syndrome** [1]. *↓ Platelet* - A **decrease in platelet count (thrombocytopenia)** is a common finding in dengue fever, often indicative of viral suppression of bone marrow or increased platelet destruction. - However, the severity of thrombocytopenia can vary, and it's not the *most universally true* or defining characteristic compared to the vector's biting habits. *Positive tourniquet test* - A **positive tourniquet test** (petechiae appearing after pressure application) is an indicator of **capillary fragility** and a sign of possible dengue, especially in endemic areas [1]. - While frequently observed in dengue, particularly in **dengue hemorrhagic fever**, it is not always positive and its absence doesn't rule out the infection [1].

Question 922: True about measles

A. Long term complication follows in form of SSPE (Correct Answer)
B. Rash appear first on leg
C. Koplik spots are seen in retina
D. Caused by DNA virus

Explanation: ***Long term complication follows in form of SSPE*** - **Subacute sclerosing panencephalitis (SSPE)** is a rare, but fatal, progressive neurodegenerative disease that can develop years after a measles infection [1]. - It is caused by persistent measles virus in the brain, leading to **neurological deterioration** and eventually death [2]. *Rash appear first on leg* - The characteristic rash of measles typically appears first on the **face and behind the ears**, then spreads downward to the trunk and extremities [1]. - The rash is usually **maculopapular** and confluent, turning brownish and fading in the same order it appeared [1]. *Koplik spots are seen in retina* - **Koplik spots** are pathognomonic for measles and are found on the **buccal mucosa** (inside the cheeks), opposite the molars [1]. - They appear as small, white, or bluish-white spots with an erythematous base before the onset of the rash. *Caused by DNA virus* - Measles is caused by the **measles virus**, which is a **single-stranded RNA virus** belonging to the genus *Morbillivirus* in the family *Paramyxoviridae*. - It is not a DNA virus; this classification has significant implications for its replication cycle and vaccine development.

Question 923: Ridley's scale is used in classification of which disease?

A. Malaria
B. Leprosy (Correct Answer)
C. Measles
D. Tuberculosis

Explanation: ***Leprosy*** - The **Ridley-Jopling classification** system is a historical and widely used method to classify leprosy based on clinical, histological, and immunological features [1]. - This scale categorizes leprosy into five forms: **tuberculoid (TT), borderline tuberculoid (BT), mid-borderline (BB), borderline lepromatous (BL), and lepromatous leprosy (LL)**, reflecting the patient's immune response to *Mycobacterium leprae* [1]. *Malaria* - Malaria is classified by **parasite species** (*Plasmodium falciparum, vivax, ovale, malariae, knowlesi*) and disease severity (uncomplicated vs. severe malaria). - There is no "Ridley's scale" involved in the classification of malaria. *Measles* - Measles, a viral disease, is typically diagnosed clinically based on its characteristic **rash, fever, cough, coryza, and conjunctivitis**. - Classification primarily involves whether it's uncomplicated or complicated (e.g., with pneumonia or encephalitis), not a specific Ridley's scale. *Tuberculosis* - Tuberculosis (TB) is classified by its **site of infection (pulmonary vs. extrapulmonary)**, bacteriological status (culture-positive or negative), and drug resistance profile. - The disease state is also described as latent TB infection (LTBI) or active TB disease; Ridley's scale is not used for TB.

Question 924: Kissing disease is also known as

A. Rubella
B. Scarlet fever
C. Acute herpetic gingivostomatitis
D. Glandular fever (Correct Answer)

Explanation: ***Glandular fever*** - **Glandular fever** is the common name for **infectious mononucleosis**, which is frequently nicknamed the "kissing disease" due to its primary transmission route through saliva [1]. - It is predominantly caused by the **Epstein-Barr virus (EBV)** [1]. *Rubella* - Rubella is commonly known as **German measles** and is also a viral infection, but it presents with a characteristic rash and is not associated with the term "kissing disease." - It can cause serious complications like **congenital rubella syndrome** if contracted during pregnancy. *Scarlet fever* - Scarlet fever is a bacterial infection caused by **Streptococcus pyogenes** (Group A Strep) and is characterized by a distinctive red rash and sore throat. - It is not referred to as the "kissing disease" and is primarily spread through respiratory droplets. *Acute herpetic gingivostomatitis* - This condition is caused by the **Herpes Simplex Virus (HSV-1)** and primarily involves inflammation and sores in the mouth and gums [2]. - While it can be transmitted via saliva, it is not commonly known as the "kissing disease" and its clinical presentation is distinct from glandular fever [2].

Question 925: Sero conversion in HIV Infection takes place in ?

A. 4 weeks (Correct Answer)
B. 12 weeks
C. 9 weeks
D. 2 weeks

Explanation: ***4 weeks*** - HIV **seroconversion**, the time when antibodies to HIV become detectable, typically occurs around **3 to 6 weeks** (approximately 4 weeks on average) after initial infection. - During this period, individuals may experience **acute retroviral syndrome**, which presents with flu-like symptoms. *12 weeks* - While 12 weeks (3 months) was historically considered the upper end of the window period for HIV antibody testing, **newer, more sensitive tests** can detect seroconversion much earlier [1]. - Waiting 12 weeks is more relevant for older generation antibody tests, not current standard tests. *9 weeks* - This falls within the broader range of the window period, but it's not the average or most common time for seroconversion with modern testing. - Many individuals will have already seroconverted by 9 weeks, especially with **third and fourth-generation tests** [1]. *2 weeks* - This is generally too early for HIV **antibody seroconversion** to reliably occur. - While some highly sensitive tests (e.g., p24 antigen or nucleic acid tests) might detect viral components this early, antibody production usually takes more time.

Question 926: Hemolytic uremic syndrome is caused by:

A. Streptococcus pneumoniae
B. Shiga toxin-producing E. coli and complement dysregulation (Correct Answer)
C. Streptococcus pneumoniae and complement dysregulation
D. Streptococcus pneumoniae and adenovirus
E. Enteroinvasive E. coli

Explanation: Shiga toxin-producing E. coli and complement dysregulation - The most common cause of **hemolytic uremic syndrome (HUS)** is infection with **Shiga toxin-producing E. coli (STEC)**, typically O157:H7, leading to typical HUS [1]. - Atypical HUS (aHUS) is primarily caused by **complement dysregulation**, often due to genetic mutations in complement regulatory proteins [1]. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* can cause HUS, but it is typically associated with **pneumococcal-associated HUS**, a less common form. - The mechanism involves neuraminidase production by the bacteria, which exposes T-antigen on red blood cells, leading to their destruction. *Streptococcus pneumoniae and complement dysregulation* - While both can cause HUS, *Streptococcus pneumoniae* and **complement dysregulation** are typically distinct causes, leading to different forms of the syndrome. - This option incorrectly combines the primary causes of two different subtypes of HUS. *Streptococcus pneumoniae and adenovirus* - *Streptococcus pneumoniae* can cause HUS, but **adenovirus** is not a generally recognized cause of HUS. - HUS is primarily linked to bacterial toxins or genetic complement defects, not typically viral infections like adenovirus. *Enteroinvasive E. coli* - **Enteroinvasive E. coli (EIEC)** causes a dysentery-like illness but does not produce Shiga toxin. - HUS is specifically triggered by toxins that damage endothelial cells, which EIEC does not produce.

Question 927: A patient presents to the emergency room with vomiting, diarrhea, high fever, and delirium. Upon physical examination, you notice large buboes, which are painful on palpation, and purpura and ecchymoses suggestive of disseminated intravascular coagulation. Gram stain on aspirate of a bubo reveals gram-negative rods with bipolar staining. Which of the following antibiotics is the drug of choice for empiric therapy?

A. Penicillin
B. Ceftazidime
C. Streptomycin (Correct Answer)
D. Chloramphenicol

Explanation: ***Streptomycin*** - The clinical presentation (high fever, delirium, **buboes**, purpura, ecchymoses, and **bipolar staining gram-negative rods**) is highly suggestive of **septicemic** or **bubonic plague** caused by *Yersinia pestis* [1]. - **Streptomycin** and **gentamicin** are the **drugs of choice** for treating plague, especially in severe forms [1]. *Penicillin* - **Penicillin** is effective against many gram-positive bacteria and some gram-negative cocci, but generally **not effective** against *Yersinia pestis*, a gram-negative rod. - Using penicillin would likely lead to treatment failure and worsening of the patient's condition given the severity of plague. *Ceftazidime* - **Ceftazidime** is a **third-generation cephalosporin** effective against a broad spectrum of gram-negative bacteria, including *Pseudomonas aeruginosa*. - While it has gram-negative coverage, it is **not considered the first-line empiric therapy** for suspected plague; aminoglycosides like streptomycin are preferred due to their established efficacy [1]. *Chloramphenicol* - **Chloramphenicol** is an effective antibiotic that can be used for plague, particularly in cases of **meningitis** due to its good central nervous system penetration. - However, for initial empiric therapy of **bubonic or septicemic plague**, **streptomycin** or **gentamicin** are generally preferred over chloramphenicol [1].

Question 928: Legionella causes:

A. Myocarditis
B. Diarrhea
C. Pontiac fever (Correct Answer)
D. All of the options

Explanation: ***Pontiac fever*** - **Pontiac fever** is a self-limiting, **flu-like illness** caused by *Legionella* species, without pneumonia. - Symptoms include fever, chills, headache, and myalgia, typically lasting 2-5 days. *Myocarditis* - While rare, **myocarditis** is not a primary or common manifestation of *Legionella* infection. - *Legionella* is primarily known for causing respiratory and, sometimes, gastrointestinal symptoms. [1] *Diarrhea* - **Diarrhea** can occur in some cases of severe *Legionella* infection, particularly **Legionnaires' disease**. - However, it is not a hallmark or exclusive symptom, and *Legionella* causes a broader spectrum of illness. *All of the options* - While *Legionella* can cause some extrapulmonary symptoms, **myocarditis** is exceedingly rare and not a characteristic feature. - **Pontiac fever** is a distinct, non-pneumonic illness caused by *Legionella*, making this option partially correct but not wholly accurate regarding the full spectrum of manifestations.

Question 929: A man with chills, fever, and headache is thought to have "atypical" pneumonia. History reveals that he raises chickens, and that approximately 2 weeks ago he lost a large number of them to an undiagnosed disease. Which of the following is the most likely diagnosis of this man's condition?

A. Leptospirosis
B. Relapsing fever
C. Anthrax
D. Ornithosis (Correct Answer)

Explanation: ***Ornithosis*** - The patient's symptoms of **chills, fever, headache, and atypical pneumonia**, combined with a history of **raising chickens** that recently died from an undiagnosed disease, are highly suggestive of ornithosis (also known as **psittacosis** or **parrot fever**). [2], [3] - This zoonotic infection is caused by **Chlamydophila psittaci** and is transmitted to humans through inhalation of contaminated aerosols from infected birds (poultry, parrots, pigeons). [2] *Leptospirosis* - **Leptospirosis** is typically associated with exposure to **contaminated water or soil** with animal urine, not direct contact with sick poultry. - While it can cause fever and headache, it often presents with **jaundice, renal failure, and hemorrhagic manifestations**, which are not mentioned here. *Relapsing fever* - **Relapsing fever** is characterized by **recurrent episodes of fever** separated by afebrile periods, caused by **Borrelia** species transmitted by lice or ticks. - The clinical presentation does not align with the typical course or epidemiological link to sick chickens. *Anthrax* - **Inhalational anthrax** can cause severe respiratory symptoms and fever but is primarily associated with exposure to **Bacillus anthracis spores**, often from infected livestock (cattle, sheep) or bioweapon exposure. [1] - The rapid death of a large number of chickens and the patient's "atypical pneumonia" do not fit the typical presentation or common transmission routes of anthrax. [1]

Question 930: Regarding yaws, all are true except -

A. Drug of choice is penicillin
B. Caused by T. pertenue
C. Cross-reactive antibodies with syphilis
D. Sexually transmitted (Correct Answer)

Explanation: ***Sexually transmitted*** - Yaws is typically transmitted through **direct skin-to-skin contact** with an infected person, especially in tropical and subtropical regions [1]. - It is **not considered a sexually transmitted infection (STI)**, differentiating it from syphilis which is caused by a related spirochete [1]. *Drug of choice is penicillin* - **Penicillin** is the highly effective and standard treatment for yaws, usually a single dose of intramuscular benzathine penicillin. - Its efficacy makes it a cornerstone of eradication efforts for this disease [1]. *Caused by T. pertenue* - Yaws is caused by **_Treponema pallidum_ subspecies _pertenue_**, a spirochete closely related to the causative agent of syphilis. - This bacterial infection leads to chronic skin, bone, and cartilage lesions [1]. *Cross-reactive antibodies with syphilis* - Due to the close genetic relationship between **_T. pallidum_ subsp. _pertenue_** (yaws) and **_T. pallidum_ subsp. _pallidum_** (syphilis), immunological tests for syphilis often show positive results in individuals with yaws. - This cross-reactivity means that standard **nontreponemal** and **treponemal tests** for syphilis cannot differentiate between the two infections without clinical context [1].

Practice by Chapter

Principles of Antimicrobial Therapy

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Fever of Unknown Origin

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HIV/AIDS and Related Infections

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Tuberculosis and Mycobacterial Diseases

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Tropical and Parasitic Infections

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Viral Infections (Hepatitis, Herpes, etc.)

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Healthcare-Associated Infections

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Fungal Infections

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Sepsis and Septic Shock

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Infection in Immunocompromised Hosts

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Emerging and Re-emerging Infections

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Antimicrobial Resistance

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Vaccination Principles

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