Infectious Diseases Practice Questions

Q: An 11-year-old boy presented with a cough for 15 days. On examination, he was found to have cervical lymphadenopathy. Lymph node biopsy showed the following findings. What could be the diagnosis?

Tuberculosis. ***Tuberculosis*** - The image likely displays **granulomatous inflammation** with **caseous necrosis**, which is highly characteristic of **tuberculosis**, especially in someone presenting with a persistent cough and lymphadenopathy. - The presence of **cervical lymphadenopathy** along with a **cough** for 15 days in an 11-year-old boy points towards extrapulmonary tuberculosis or primary tuberculosis infection affecting the mediastinal lymph nodes with cervical involvement. *Leprosy* - While leprosy also causes granulomas, it typically manifests as skin lesions and nerve involvement, and lymphadenopathy is less common or specific as the primary initial presentation. - The granulomas in leprosy are often **epithelioid** with **foamy histiocytes** and numerous acid-fast bacilli, which are not explicitly described or obvious in the provided context for a definitive diagnosis without special stains. *Sarcoidosis* - Sarcoidosis involves **non-caseating granulomas**, meaning there is no central necrosis, which is a key differentiating feature from the caseating necrosis often seen in tuberculosis. - Although sarcoidosis can cause lymphadenopathy and cough, the microscopic features in the image, particularly if showing necrosis, would argue against sarcoidosis. *Syphilis* - Syphilis can cause lymphadenopathy (especially in secondary syphilis), but the characteristic histological finding is usually a **plasma cell-rich infiltrate** with **endarteritis obliterans**, not typically prominent granulomas with caseous necrosis. - Clinical presentation with cough and chronic lymphadenopathy in an 11-year-old would also make syphilis a less likely primary consideration without other suggestive signs.

Q: After 4 months of renal transplantation, which infection is most likely to develop?

Cytomegalovirus (CMV). ***Cytomegalovirus (CMV)*** - **CMV infection** or reactivation is most common in transplant recipients between 1 and 6 months post-transplantation, often peaking around 3-4 months when immunosuppression is high [1]. - It can cause a wide range of clinical syndromes, including **fever**, **leukopenia**, **gastroenteritis**, and organ-specific disease in immunocompromised individuals [1]. *EBV* - **Epstein-Barr virus (EBV)** is primarily associated with **post-transplant lymphoproliferative disorder (PTLD)**, which tends to occur later, typically more than 6 months after transplantation, especially in pediatric recipients [1]. - While EBV can reactivate, severe clinical disease or PTLD is less likely to peak at 4 months compared to CMV [1]. *Candida* - **Candida infections** are typically **early complications** after transplantation, usually occurring within the first month [1]. - They are often related to indwelling catheters, antibiotics, and surgical anastomoses, making them less likely to be the most common infection at 4 months. *Histoplasma* - **Histoplasma capsulatum** causes **histoplasmosis**, a fungal infection prevalent in endemic areas (e.g., Ohio and Mississippi River valleys). - While possible in immunocompromised patients, it's generally an **opportunistic infection** that can occur at any time, but is less specific to the 4-month post-transplant window compared to CMV.

Q: Which of the following conditions is least associated with HIV infection?

Tertiary syphilis. ***Tertiary syphilis*** - While syphilis can be more aggressive in HIV-positive individuals, **tertiary syphilis** (e.g., gummas, neurosyphilis, cardiovascular syphilis) is not specifically or exclusively associated with HIV infection itself, but rather the untreated progression of syphilis within an immunocompromised host [1]. - The other conditions listed are **AIDS-defining illnesses** or strongly associated with the severe immunodeficiency caused by HIV [1]. *Oesophageal candidiasis* - This is an **AIDS-defining illness**, indicating severe immunosuppression in HIV-positive individuals [1]. - It results from an overgrowth of *Candida albicans* due to a compromised immune system [1]. *Kaposi sarcoma* - This is a cancer caused by **human herpesvirus 8 (HHV-8)**, and its incidence is significantly increased in HIV-infected individuals, leading to its classification as an **AIDS-defining illness** [1]. - It presents as vascular lesions on the skin, mucous membranes, lymph nodes, or internal organs [1]. *Primary CNS lymphoma* - This is another **AIDS-defining illness** that occurs with increased frequency in HIV-positive individuals, particularly those with advanced immunosuppression [1]. - It is often associated with the **Epstein-Barr virus (EBV)** in this population [1].

Q: A patient presents with hoarseness of voice and a clinical condition as shown in the image. Identify the lesion:

Diphtheria. ***Diphtheria*** - The image shows a **thick, grayish-white pseudomembrane** covering the tonsils and likely extending to other parts of the pharynx, which is a classic sign of diphtheria. - **Hoarseness** indicates laryngeal involvement, a severe complication of diphtheria due to pseudomembrane formation extending to the larynx, potentially causing airway obstruction. *Follicular tonsillitis* - This condition presents with **pus-filled follicles** or spots on the tonsils, which are typically yellow or white, rather than a confluent membrane. - While it causes throat pain and fever, it generally does not lead to the formation of a **firm, adherent pseudomembrane** or significant hoarseness from laryngeal obstruction as seen in diphtheria. *Aphthous ulcer* - An aphthous ulcer is a **small, painful, shallow sore** with a white or yellowish center and a red border, typically found on the non-keratinized oral mucosa. - It does not present as a widespread, thick membranous lesion covering the tonsils and causing hoarseness. *Membranous tonsillitis* - While "membranous tonsillitis" describes the presence of a membrane on the tonsils, this term is often used generally. However, the specific characteristics in the image (thick, grayish, adherent membrane with severe symptoms like hoarseness) are pathognomonic for **diphtheria**. - Other causes of membranous tonsillitis, such as infectious mononucleosis, typically present with a less adherent membrane and often lack the severe systemic toxicity and potential for rapid airway compromise seen in diphtheria.

Q: A patient complains about painful blisters around the angle of mouth, identify the pathogen

Herpes Simplex Virus type 1 (HSV-1). ***Herpes Simplex Virus type 1 (HSV-1)*** - HSV-1 is the primary cause of **oral herpes**, commonly presenting as **cold sores** or **fever blisters** around the mouth [1]. - The characteristic painful blisters at the angle of the mouth are typical of **recurrent HSV-1 infection** [1]. *Coxsackievirus* - Coxsackievirus primarily causes **hand-foot-and-mouth disease** or **herpangina**, characterized by lesions on the hands, feet, and inside the mouth/throat, not typically painful blisters around the external angle of the mouth [2]. - It often presents with a **rash** and **fever** in children [2]. *Epstein-Barr Virus* - Epstein-Barr Virus (EBV) is the causative agent of **infectious mononucleosis**, which presents with **fatigue**, **fever**, **sore throat**, and **lymphadenopathy**. - It does not typically cause painful blisters around the mouth. *Varicella-Zoster Virus* - Varicella-Zoster Virus (VZV) causes **chickenpox** (primary infection) and **shingles** (reactivation) [3]. - While shingles can cause painful blisters, it typically follows a **dermatomal distribution** and is not localized to the angle of the mouth in this manner [3].

Q: What are the essential major blood culture criteria for diagnosing infective endocarditis?

Single positive culture of Coxiella burnetii. ***Single positive culture of Coxiella burnetii*** - A single positive blood culture for **Coxiella burnetii** or **anti-phase I IgG antibody titer > 1:800** is considered a major criterion for infective endocarditis due to its highly pathogenic nature in this context [1], [2]. - This organism is a known cause of **culture-negative endocarditis**, and specific serology or molecular tests are often required for diagnosis [1]. *Single positive culture of Corynebacterium species* - **Corynebacterium species** are often considered **contaminants** in blood cultures, especially *Corynebacterium jeikeium*, and typically require multiple positive cultures, often from different sites, to be considered significant pathogens for infective endocarditis [2]. - A single positive culture of these organisms alone is generally insufficient to meet major diagnostic criteria for endocarditis [2]. *Both HACEK and Coxiella cultures* - While both **HACEK organisms** and **Coxiella burnetii** can cause endocarditis, the combination of both is not a specific major criterion in itself. - The diagnostic criteria address each organism individually [2]. *Single positive culture of HACEK group* - **HACEK organisms** (**H**aemophilus, **A**ggregatibacter, **C**ardiobacterium, **E**ikenella, **K**ingella) are well-known causes of endocarditis, but usually require **two separate positive blood cultures** for infective endocarditis major criteria [2]. - A single positive culture of a HACEK organism is typically classified as a minor criterion unless other supporting evidence is present.

Q: Which virus is typically associated with serpiginous ulcers in the distal esophagus?

CMV. CMV - Serpiginous ulcers in the distal esophagus are indicative of **cytomegalovirus (CMV) esophagitis**, especially in immunocompromised patients. - CMV infection can lead to **ulcerative lesions** that have a characteristic serpentine appearance, differentiating it from other causes. *Pill* - Pill-induced esophagitis generally results in **localized ulcers** rather than serpiginous ones and is often associated with the use of certain medications. - Symptoms typically include **dysphagia** and **odynophagia**, without the characteristic serpentine ulcer morphology. *Corrosive* - Corrosive injuries from chemicals present as **burn-like lesions** and strictures rather than serpiginous ulcers; the morphology is quite distinct. - These injuries usually occur due to ingestion of strong acids or alkalis, leading to **necrosis**, and don't show typical serpiginous ulceration. *Herpes* - Herpes simplex virus usually causes **multiple shallow ulcers** rather than deep, serpiginous ulcers, and is more commonly observed in the form of **vesicular lesions**. - Typically it presents with fever and significant **pain**, which is not the primary characteristic of CMV esophagitis.

Q: Pneumocystis jirovecii, typically seen in immunocompromised patients, is a:

Fungus. ***Fungus*** - *Pneumocystis jirovecii* is a **yeast-like fungus** that causes severe lung infections, particularly in individuals with **compromised immune systems**, such as those with HIV/AIDS. - Its classification has evolved, but it is now firmly established as a fungus based on its **genetic makeup** and cell wall structure. *Bacteria* - Bacteria are single-celled microorganisms that belong to the kingdom **Prokaryotae**, lacking a true nucleus and membrane-bound organelles. - While bacteria can cause pneumonia in immunocompromised patients, *Pneumocystis jirovecii* has a distinct **eukaryotic cell structure** and genetic characteristics of fungi. *Virus* - Viruses are **acellular infectious agents** that replicate only inside the living cells of other organisms. - Viruses cause a wide range of infections, but *Pneumocystis jirovecii* possesses its own **cellular machinery** and metabolic pathways, classifying it outside the viral domain. *Parasite* - Parasites are organisms that live on or in a host organism and obtain their food at the expense of their host. - Although *Pneumocystis jirovecii* was historically misclassified as a protozoan parasite due to its morphology, molecular studies have since confirmed its **fungal lineage**.

Q: A boy presented with multiple non suppurative osteomyelitis with sickle cell anaemia. What will be the causative organism?

Salmonella. ***Salmonella*** - **Salmonella species** are a well-known cause of **osteomyelitis** in patients with **sickle cell anemia**, due to factors like gut mucosal damage and functional asplenia. [1] - The unique pathophysiology of sickle cell disease, including areas of bone infarction and compromised reticulendothelial system function, predisposes these patients to **Salmonella infections**. [1] *Staphylococcus aureus* - While **Staphylococcus aureus** is the most common cause of osteomyelitis in the general population, it is less likely to be the causative organism in patients with **sickle cell anemia** compared to Salmonella. - Its presence usually indicates other predisposing factors like trauma or prosthetic devices. *H. influenzae* - **Haemophilus influenzae** was a common cause of osteomyelitis in children before widespread vaccination but is now rare, especially with routine immunizations. - It is not specifically associated with a higher risk in patients with **sickle cell disease** for osteomyelitis compared to other pathogens. *Enterobacter species* - **Enterobacter species** can cause osteomyelitis, particularly in immunocompromised individuals or following surgery, but they are not uniquely associated with **sickle cell anemia** as a primary cause compared to Salmonella. - Their involvement in non-suppurative osteomyelitis in this specific patient population is less common.

Question 1

An 11-year-old boy presented with a cough for 15 days. On examination, he was found to have cervical lymphadenopathy. Lymph node biopsy showed the following findings. What could be the diagnosis?

Accepted Answer

Tuberculosis

Answer

Leprosy

Answer

Sarcoidosis

Answer

Syphilis

Question 2

After 4 months of renal transplantation, which infection is most likely to develop?

Accepted Answer

Cytomegalovirus (CMV)

Answer

EBV

Answer

Candida

Answer

Histoplasma

Question 3

Which of the following conditions is least associated with HIV infection?

Accepted Answer

Tertiary syphilis

Answer

Kaposi sarcoma

Answer

Oesophageal candidiasis

Answer

Primary CNS lymphoma

Question 4

A patient presents with hoarseness of voice and a clinical condition as shown in the image. Identify the lesion:

Accepted Answer

Diphtheria

Answer

Follicular tonsillitis

Answer

Aphthous ulcer

Answer

Membranous tonsillitis

Question 5

A patient complains about painful blisters around the angle of mouth, identify the pathogen

Accepted Answer

Herpes Simplex Virus type 1 (HSV-1)

Answer

Coxsackievirus

Answer

Epstein-Barr Virus

Answer

Varicella-Zoster Virus

Question 6

What are the essential major blood culture criteria for diagnosing infective endocarditis?

Accepted Answer

Single positive culture of Coxiella burnetii

Answer

Single positive culture of Corynebacterium species

Answer

Both HACEK and Coxiella cultures

Answer

Single positive culture of HACEK group

Question 7

Which virus is typically associated with serpiginous ulcers in the distal esophagus?

Accepted Answer

CMV

Answer

Herpes

Answer

Pill

Answer

Corrosive

Question 8

Pneumocystis jirovecii, typically seen in immunocompromised patients, is a:

Accepted Answer

Fungus

Answer

Parasite

Answer

Virus

Answer

Bacteria

Question 9

A boy presented with multiple non suppurative osteomyelitis with sickle cell anaemia. What will be the causative organism?

Accepted Answer

Salmonella

Answer

H. influenzae

Answer

Enterobacter species

Answer

Staphylococcus aureus

Question 10

What is the most commonly recommended COMPLETE antiretroviral regimen for a pregnant woman with HIV infection?

Accepted Answer

Tenofovir disoproxil fumarate/emtricitabine/dolutegravir

Answer

Abacavir/lamivudine

Answer

Didanosine/stavudine

Answer

Tenofovir disoproxil fumarate/emtricitabine (2-drug regimen)

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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