Infectious Diseases Practice Questions

Q: Blood culture is positive in which infection caused by Staphylococcus aureus?

Infective endocarditis. ***Infective endocarditis*** - **Infective endocarditis** is characterized by the presence of bacteria in the bloodstream, leading to a **positive blood culture** [2]. *Staphylococcus aureus* is a common cause, particularly in intravenous drug users [1], [2]. - The infection involves the **endothelial lining of the heart**, often affecting heart valves, causing vegetations that can shed bacteria into the circulation [2], [3]. *Toxic Shock Syndrome (TSS)* - TSS is caused by toxins (e.g., **TSST-1**) produced by *Staphylococcus aureus*, not by the direct presence of bacteria in the bloodstream in high numbers that would consistently yield a positive blood culture. - While *S. aureus* is present, the systemic effects are primarily **toxin-mediated**, and blood cultures are often negative. *Impetigo* - Impetigo is a **superficial skin infection** caused by *Staphylococcus aureus* or *Streptococcus pyogenes*. - It does not involve systemic bacteremia, so **blood cultures are typically negative**. *Staphylococcal Scalded Skin Syndrome (SSSS)* - SSSS is a **toxin-mediated disease** caused by exfoliatin toxins produced by *Staphylococcus aureus*. - The bacteria usually remain localized at the site of infection (e.g., nose, throat, or skin), and **blood cultures are generally negative**.

Q: The most common site for amoebiasis is:

Caecum. ***Caecum*** - The **caecum** is the most common site for intestinal amoebiasis because it provides an ideal environment for the **trophozoites** of *Entamoeba histolytica* to embed and colonize [1]. - The slower transit time and abundant bacterial flora in the caecum contribute to its susceptibility to **amoebic invasion and ulceration**. *Sigmoid colon* - While the sigmoid colon can be affected by amoebiasis, leading to symptoms like **dysentery**, it is not the initial or most frequent site of colonization [1]. - Involvement of the sigmoid colon typically indicates more widespread or severe intestinal infection. *Transverse colon* - The transverse colon can also be involved in amoebiasis, especially in cases of extensive disease, but it is less commonly the primary site compared to the caecum. - Symptoms related to transverse colon involvement are often diffuse and can include **abdominal pain** and **tenderness**. *Liver* - The **liver** is the most common site for **extraintestinal amoebiasis**, leading to an **amoebic liver abscess** [1]. - However, the question asks for the most common site for amoebiasis in general, implying initial infection, which is typically in the intestine (specifically the caecum).

Q: Loeffler's syndrome occurs in all except:

Giardia. ***Giardia*** - **Giardia lamblia** is an intestinal flagellate that causes **giardiasis**, primarily presenting with gastrointestinal symptoms such as diarrhea, abdominal cramps, and malabsorption [1]. - It does not undergo a **pulmonary migration phase** in its life cycle, which is a prerequisite for causing eosinophilic pneumonitis (Loeffler's syndrome). *Toxocara* - **Toxocara canis** and **Toxocara cati** larvae migrate through the lungs, causing **visceral larva migrans (VLM)** and pulmonary eosinophilia [1]. - This migration can trigger an immune response in the lungs, leading to symptoms consistent with **Loeffler's syndrome**. *Strongyloides* - **Strongyloides stercoralis** larvae migrate through the lungs as part of their life cycle (both in initial infection and in auto-infection), which can cause **eosinophilic pneumonitis** [1]. - This pulmonary migration commonly results in respiratory symptoms and is associated with **Loeffler's syndrome**. *Ascaris* - **Ascaris lumbricoides** larvae undergo essential **pulmonary migration** after ingestion, breaking out of capillaries into the alveoli before being coughed up and swallowed [1]. - This larval migration through the lungs is a classic cause of **Loeffler's syndrome**, characterized by transient pulmonary infiltrates and eosinophilia [1].

Q: A 3-year-old child presented with fatigue, malaise, fever, sore throat, headache, nausea, abdominal pain, and myalgia. On examination, generalized lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, palatal petechiae, rashes, and edema of the eyelids were observed. Some unusual cells were seen in the peripheral blood. A specific serological test was performed. What is the receptor involved in the pathogenesis of the disease associated with these symptoms?

CD21. ***CD21*** - The constellation of symptoms (fatigue, fever, sore throat, lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, palatal petechiae, edema of eyelids, and atypical lymphocytes) in a child strongly suggests **infectious mononucleosis**, which is most commonly caused by the **Epstein-Barr Virus (EBV)** [1]. - EBV primarily infects **B lymphocytes** by binding to the **CD21 receptor** (also known as complement receptor type 2, CR2) on the B cell surface. *CD20* - **CD20** is another transmembrane protein found on the surface of B lymphocytes, but it is not the primary receptor used by EBV for entry. - It plays a role in B cell activation and is a target for immunotherapy in some B cell malignancies. *CD19* - **CD19** is a B-cell specific surface marker that is part of a receptor complex involved in B cell activation and growth. - While present on B cells, it is not the direct receptor that EBV uses to enter the cell. *CD117* - **CD117** (c-Kit receptor) is a receptor tyrosine kinase primarily found on hematopoietic stem cells, mast cells, and interstitial cells of Cajal. - It is not expressed on B lymphocytes and is therefore not involved in EBV infection.

Q: Which of the following is more frequently associated with Klebsiella pneumoniae than with Pseudomonas aeruginosa?

Upper lobe cavitation. Upper lobe cavitation - **Upper lobe cavitation** is a characteristic feature of pneumonia caused by **Klebsiella pneumoniae**, particularly in chronic alcoholics or individuals with poor host defenses [1]. - While *Pseudomonas aeruginosa* can cause severe pneumonia, **cavitary lesions** are less frequently reported and typically occur in immunocompromised patients. *Artificial ventilation* - **Artificial ventilation** is a significant risk factor for nosocomial pneumonia caused by both *Klebsiella pneumoniae* and *Pseudomonas aeruginosa*. - However, the question asks for a feature *more frequently associated* with *Klebsiella pneumoniae*, and ventilation is a common risk for both. *Cystic fibrosis* - **Cystic fibrosis** is overwhelmingly associated with chronic *Pseudomonas aeruginosa* infections, which establish persistent biofilms in the respiratory tract. - While *Klebsiella pneumoniae* can colonize CF patients, it is not the primary or most frequent pathogen linked to this condition. *Diabetes mellitus* - **Diabetes mellitus** increases susceptibility to various infections, including those caused by *Klebsiella pneumoniae* and *Pseudomonas aeruginosa*. - However, it is an underlying condition and not a specific clinical characteristic of the pneumonia itself that differentiates the two organisms.

Q: Romana's sign is seen in infection due to:

Trypanosoma cruzi. ***Trypanosoma cruzi*** - **Romana's sign** is characteristic of the **acute phase** of **Chagas disease**, caused by *Trypanosoma cruzi*. - It presents as **unilateral periorbital edema** and swelling, indicating the site of parasite entry, often from the bite of a **reduviid bug** near the eye or by rubbing the parasite-laden feces into the eye. *Trypanosoma brucei* - This parasite causes **African trypanosomiasis** (sleeping sickness), which presents with distinct symptoms like **fever**, **headache**, **lymphadenopathy** (winterbottom's sign), and later neurological involvement [2]. - Ocular signs are not typically a primary or diagnostic feature in the way Romana's sign is for Chagas disease. *Leishmania donovani* - *Leishmania donovani* is the causative agent of **visceral leishmaniasis** (**kala-azar**), characterized by **fever**, **splenomegaly**, **hepatomegaly**, and **pancytopenia** [1]. - It does not cause Romana's sign; ocular involvement, if present, is usually different and not a hallmark diagnostic feature. *Onchocerca volvulus* - This filarial nematode causes **onchocerciasis** (river blindness), primarily associated with **subcutaneous nodules**, **dermatitis**, and **ocular lesions** leading to blindness. - While it causes eye pathology, it does not involve the specific periorbital edema known as Romana's sign.

Q: Mucormycosis of the paranasal sinus is most common in?

Diabetes. Diabetes - **Diabetic ketoacidosis** significantly impairs neutrophil function, reducing the body's ability to resist fungal infections like mucormycosis. [1] - The **hyperglycemic** and **acidotic** environment in uncontrolled diabetes promotes the growth and invasiveness of Mucorales fungi. [1] *Individuals with HIV* - While HIV can lead to **immunocompromise**, mucormycosis is less common in this population than in those with diabetes; other opportunistic infections are more prevalent with HIV. - HIV primarily affects **CD4+ T-lymphocytes**, whereas mucormycosis is more often associated with defects in phagocytic function. *Individuals on immunosuppressive therapy* - **Immunosuppressive therapy**, such as corticosteroids or chemotherapy, can increase the risk of fungal infections, but **uncontrolled diabetes** is the most significant risk factor for rhinocerebral mucormycosis. [1] - The type of immunosuppression and underlying condition are critical; while relevant, it is not as uniquely predisposing as diabetic ketoacidosis. [1] *Patients who have undergone surgery* - Surgical patients, especially those with prolonged hospital stays or extensive wounds, can be susceptible to various infections, but mucormycosis is not specifically or most commonly linked to surgery as an isolated risk factor. - **Nosocomial infections** after surgery are often bacterial; fungal infections, when they occur, are typically associated with profound immunosuppression or specific device-related issues, not surgery alone.

Q: Which of the following statements about hyperplastic tuberculosis is false?

Surgery is the primary treatment modality.. ***Surgery is the primary treatment modality.*** - This statement is **false** because while surgery may have a role in complicated cases of hyperplastic tuberculosis (e.g., obstruction, perforation, massive bleeding), **antitubercular therapy (ATT)** is the primary and initial treatment modality for intestinal tuberculosis. - Surgery is typically reserved for patients who do not respond to ATT or present with complications that require surgical intervention for immediate relief. *Most common site is the ileocecal region.* - This statement is **true** because the **ileocecal region** is indeed the most common site for intestinal tuberculosis due to its rich lymphatic tissue, relative stasis of intestinal contents, and increased absorption. - The Peyer's patches in the ileum are particularly susceptible to Mycobacterium tuberculosis infection. *Presents as a mass in the right iliac fossa.* - This statement is **true** as hyperplastic intestinal tuberculosis often leads to **fibrotic thickening** of the bowel wall and mesentery, forming a palpable mass. - The **right iliac fossa** is the common location for such a mass due to the frequent involvement of the ileocecal region. *Antitubercular therapy is the treatment of choice.* - This statement is **true** as **antitubercular therapy (ATT)**, a multi-drug regimen, is the cornerstone of treatment for all forms of tuberculosis, including hyperplastic intestinal tuberculosis. - ATT aims to eradicate the infection, reduce inflammation, and prevent complications.

Q: Which of the following structures is least likely to be affected by gonococcus?

Testis. ***Testis*** - The **testis** itself is relatively protected from direct gonococcal infection and is thus least likely to be primarily affected. - While epididymitis can occur due to gonococcus, orchitis (inflammation of the testis) without epididymitis is rare and generally caused by other pathogens like mumps virus. *Urethra* - The **urethra** is the most common site of initial gonococcal infection in males, leading to **urethritis** [1]. - Symptoms often include dysuria and purulent discharge [1]. *Prostate* - The **prostate** can be affected by ascending gonococcal infection from the urethra, leading to **prostatitis**. - This typically presents with pelvic pain, dysuria, and fever. *Seminal vesicle* - The **seminal vesicles** can also be involved in ascending gonococcal infections, often alongside epididymitis or prostatitis. - Inflammation can contribute to pain and reproductive complications.

Q: The most common cause of sporadic viral encephalitis is what?

Herpes simplex encephalitis. ***Herpes simplex encephalitis*** - **Herpes simplex virus (HSV)**, particularly **HSV-1**, is the most frequent cause of **sporadic viral encephalitis** globally. - It often presents with characteristic temporal lobe involvement, leading to **focal neurological deficits** and **seizures** [1]. *Japanese B encephalitis* - This is a prominent cause of **epidemic viral encephalitis** in Asia, primarily affecting children, but not the most common cause of **sporadic cases**. - It is transmitted by **mosquitoes** and typically has a seasonal pattern. *Human immunodeficiency virus encephalitis* - HIV can cause **encephalopathy** and dementia in advanced stages, but it is not typically characterized as **acute viral encephalitis** [1]. - The neurological manifestations of HIV are more chronic and progressive rather than an acute inflammatory process of the brain [1]. *Rubeola encephalitis* - **Rubeola (measles virus)** can cause acute post-infectious encephalomyelitis or the rare, fatal, late-onset condition **subacute sclerosing panencephalitis (SSPE)**. - While serious, these conditions are not the most common cause of **sporadic acute viral encephalitis** in the general population.

Question 1

Blood culture is positive in which infection caused by Staphylococcus aureus?

Accepted Answer

Infective endocarditis

Answer

Impetigo

Answer

Toxic Shock Syndrome (TSS)

Answer

Staphylococcal Scalded Skin Syndrome (SSSS)

Question 2

The most common site for amoebiasis is:

Accepted Answer

Caecum

Answer

Sigmoid colon

Answer

Transverse colon

Answer

Liver

Question 3

Loeffler's syndrome occurs in all except:

Accepted Answer

Giardia

Answer

Toxocara

Answer

Strongyloides

Answer

Ascaris

Question 4

A 3-year-old child presented with fatigue, malaise, fever, sore throat, headache, nausea, abdominal pain, and myalgia. On examination, generalized lymphadenopathy, hepatosplenomegaly, tonsillar enlargement, palatal petechiae, rashes, and edema of the eyelids were observed. Some unusual cells were seen in the peripheral blood. A specific serological test was performed. What is the receptor involved in the pathogenesis of the disease associated with these symptoms?

Accepted Answer

CD21

Answer

CD20

Answer

CD19

Answer

CD117

Question 5

Which of the following is more frequently associated with Klebsiella pneumoniae than with Pseudomonas aeruginosa?

Accepted Answer

Upper lobe cavitation

Answer

Cystic fibrosis

Answer

Diabetes mellitus

Answer

Artificial ventilation

Question 6

Romana's sign is seen in infection due to:

Accepted Answer

Trypanosoma cruzi

Answer

Trypanosoma brucei

Answer

Leishmania donovani

Answer

Onchocerca volvulus

Question 7

Mucormycosis of the paranasal sinus is most common in?

Accepted Answer

Diabetes

Answer

Individuals with HIV

Answer

Individuals on immunosuppressive therapy

Answer

Patients who have undergone surgery

Question 8

Which of the following statements about hyperplastic tuberculosis is false?

Accepted Answer

Surgery is the primary treatment modality.

Answer

Antitubercular therapy is the treatment of choice.

Answer

Most common site is the ileocecal region.

Answer

Presents as a mass in the right iliac fossa.

Question 9

Which of the following structures is least likely to be affected by gonococcus?

Accepted Answer

Testis

Answer

Seminal vesicle

Answer

Urethra

Answer

Prostate

Question 10

The most common cause of sporadic viral encephalitis is what?

Accepted Answer

Herpes simplex encephalitis

Answer

Japanese B encephalitis

Answer

Human immunodeficiency virus encephalitis

Answer

Rubeola encephalitis

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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