Infectious Diseases Practice Questions

Q: A 45-year-old woman is undergoing chemotherapy for breast cancer and presents 10 days after her last treatment with fever (temperature >38.5°C) and a sore throat. On examination, she has oral mucositis, and her WBC count is 800/mL with an absolute neutrophil count below 500/mL. Other investigations, including CXR, urinalysis, and biochemistry, are normal. What is the most appropriate next step in management?

Start empiric bacterial antibiotics.. This patient presents with **Febrile Neutropenia**, defined as a single oral temperature of >38.3°C (or >38.0°C sustained for 1 hour) and an Absolute Neutrophil Count (ANC) <500 cells/mm³. This is a medical emergency in oncology patients [1]. **1. Why Option A is Correct:** In neutropenic patients, the inflammatory response is blunted, making fever often the only sign of a life-threatening infection [1]. The most common pathogens are skin and gut flora (e.g., *Pseudomonas aeruginosa*, *Staphylococcus aureus*). Because these infections can progress to septic shock within hours, **immediate empiric broad-spectrum intravenous antibiotics** (e.g., Piperacillin-Tazobactam, Cefepime, or Meropenem) must be started after blood cultures are drawn, without waiting for results [2]. **2. Why Other Options are Incorrect:** * **Option B:** Empiric antifungal therapy is typically reserved for patients who remain febrile after 4–7 days of broad-spectrum antibiotics and have no identified source. * **Option C:** Delaying antibiotics to wait for cultures is dangerous and associated with high mortality in neutropenic sepsis. * **Option D:** While mucositis can be associated with HSV, the primary threat to life is bacterial translocation; antivirals are not the first-line empiric treatment for fever unless specific lesions are present. **Clinical Pearls for NEET-PG:** * **ANC Calculation:** Total WBC × (% Neutrophils + % Bands). * **MASCC Score:** Used to determine if a patient is low-risk (eligible for oral antibiotics) or high-risk (requires IV admission). * **Monotherapy:** For most cases, anti-pseudomonal beta-lactam monotherapy is sufficient. Vancomycin is added only if there is clinical suspicion of MRSA, catheter infection, or skin/soft tissue edition.

Q: A 20-year-old woman presents with fever, severe myalgia and arthralgia, pain behind the eyes, and rash for 3 days. Lab reports show thrombocytopenia and leucopenia. What is the most likely diagnosis?

Dengue fever. ### Explanation **Correct Option: B. Dengue fever** The clinical presentation is classic for **Dengue Fever**, often referred to as **"Break-bone fever"** due to the characteristic severe myalgia and arthralgia. The combination of high-grade fever, **retro-orbital pain** (pain behind the eyes), and a maculopapular rash is highly suggestive. Laboratory findings of **thrombocytopenia** (low platelets) and **leucopenia** (low WBC count) are hallmark features of the early phase of Dengue infection caused by the *Flavivirus* (transmitted by the *Aedes aegypti* mosquito). **Why other options are incorrect:** * **A. Malaria:** While it presents with fever and thrombocytopenia, it typically features cyclical paroxysms (chills/rigors) and splenomegaly. Retro-orbital pain and severe arthralgia are not primary features. * **C. Typhoid:** Presents with a "step-ladder" pattern fever, bradycardia (Faget’s sign), and abdominal symptoms. While leucopenia can occur, the severe "break-bone" pains and retro-orbital pain are absent. * **D. Yellow fever:** Though also a *Flavivirus*, it is characterized by jaundice (icterus), hematemesis (black vomit), and Councilman bodies on liver biopsy. It is not endemic in India. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Aedes aegypti* (Day biter; breeds in artificial collections of clean water). * **Serology:** **NS1 Antigen** is the marker of choice for the first 5 days. **IgM ELISA** is used after day 5. * **Tourniquet Test:** A positive test (≥10 petechiae/square inch) indicates capillary fragility. * **Critical Phase:** Occurs during defervescence (when fever drops); this is when plasma leakage and Dengue Shock Syndrome (DSS) are most likely to occur.

Q: What is the most common malignancy in patients with HIV?

Lymphoma. **Explanation:** In the era of **Highly Active Antiretroviral Therapy (HAART)**, the epidemiology of malignancies in HIV patients has shifted. While Kaposi Sarcoma (KS) was historically the most common, **Non-Hodgkin Lymphoma (NHL)** is now recognized as the most common malignancy overall in HIV-infected individuals [2]. **Why Lymphoma is Correct:** HIV-associated lymphomas are primarily B-cell in origin (e.g., Diffuse Large B-cell Lymphoma and Burkitt Lymphoma). The underlying mechanism involves chronic B-cell activation, immune dysregulation, and the oncogenic role of co-infections like **Epstein-Barr Virus (EBV)** and **HHV-8** [2]. These are classified as "AIDS-Defining Illnesses." **Analysis of Incorrect Options:** * **B. Squamous Cell Carcinoma (SCC):** While HIV patients have a higher risk of SCC (particularly anal and cervical due to HPV co-infection), it is not as prevalent as lymphoma. * **C. Adenocarcinoma:** Though the risk of lung adenocarcinoma is increased in HIV patients (often due to high smoking rates), it is not the most common malignancy. * **D. Fibroma:** These are benign connective tissue tumors and are not specifically associated with or common in HIV. **High-Yield Clinical Pearls for NEET-PG:** * **Most common AIDS-defining malignancy:** Non-Hodgkin Lymphoma (specifically DLBCL). * **Most common "Non-AIDS Defining" malignancy:** Lung Cancer. * **Primary CNS Lymphoma:** Strongly associated with **EBV**; it is a critical differential for ring-enhancing lesions on MRI (alongside Toxoplasmosis). * **Kaposi Sarcoma:** Caused by **HHV-8**; it presents as violaceous skin lesions and was the most common malignancy *before* the widespread use of HAART [1].

Q: Antiretroviral drugs are started for HIV/AIDS patients if the CD4 count is:

Any CD4 count. **Explanation:** The management of HIV has evolved significantly over the last decade. The correct answer is **D (Any CD4 count)**, reflecting the current **"Test and Treat"** policy. **1. Why "Any CD4 count" is correct:** Current WHO and National AIDS Control Organization (NACO) guidelines recommend that Antiretroviral Therapy (ART) should be initiated in **all** individuals living with HIV, regardless of their clinical stage or CD4 cell count [1]. This shift is based on the **START (Strategic Timing of AntiRetroviral Treatment) trial**, which demonstrated that early initiation of ART significantly reduces the risk of AIDS-defining events, non-AIDS-related complications (like cardiovascular or renal disease), and prevents horizontal transmission of the virus (U=U: Undetectable = Untransmittable). **2. Why other options are incorrect:** * **Options A, B, and C:** Historically, ART was deferred until the immune system showed signs of failure to avoid drug toxicity and preserve future options. Previous thresholds were <200 (1990s), <350 (2010), and <500 (2013) [3]. These are now considered outdated as the benefits of early viral suppression far outweigh the risks of early drug exposure. **High-Yield Clinical Pearls for NEET-PG:** * **First-line ART Regimen (NACO):** TLD regimen — **T**enofovir (TDF) + **L**amivudine (3TC) + **D**olutegravir (DTG) [1]. * **Exception to Immediate Start:** In cases of **Cryptococcal Meningitis** or **Tubercular Meningitis**, ART is typically delayed by 4–6 weeks to prevent a life-threatening Immune Reconstitution Inflammatory Syndrome (IRIS) [4]. * **Monitoring:** Viral load is the preferred tool for monitoring ART response (Target: <50 copies/ml). CD4 count is used primarily to assess the need for opportunistic infection prophylaxis (e.g., Co-trimoxazole if CD4 <200) [2].

Q: Rigidity of facial muscles, 'Risus sardonicus', is associated with which condition?

Tetanus. **Explanation:** **Tetanus** is the correct answer. It is caused by the neurotoxin **tetanospasmin** produced by *Clostridium tetani*. The toxin acts by blocking the release of inhibitory neurotransmitters (GABA and Glycine) from Renshaw cells in the spinal cord. This leads to unchecked excitatory impulses, resulting in generalized muscle rigidity and spasms. * **Risus sardonicus** (Sardonic smile) is a characteristic clinical sign caused by the sustained spasm of the facial muscles (specifically the *frontalis* and *orbicularis oris*). * **Trismus** (Lockjaw) is often the presenting symptom due to masseter muscle involvement. **Analysis of Incorrect Options:** * **Tetany:** Caused by hypocalcemia, it presents with carpopedal spasm and neuromuscular irritability (Chvostek’s and Trousseau’s signs), but not the classic "sardonic smile" of tetanus. * **Leprosy:** While it can cause facial nerve palsy (leading to sagging or inability to close eyes), it does not cause spastic rigidity or Risus sardonicus. * **Actinomycosis:** Known for causing "lumpy jaw" with chronic granulomatous lesions and sulfur granules, it involves local swelling rather than generalized muscle spasms. **High-Yield Clinical Pearls for NEET-PG:** * **Opisthotonus:** A backward arching of the spine caused by powerful extensor muscle spasms. * **Mechanism:** Retrograde axonal transport of the toxin to the CNS. * **Management:** Wound debridement, Metronidazole (preferred over Penicillin as Penicillin is a GABA antagonist), and Tetanus Immunoglobulin (TIG). * **Neonatal Tetanus:** Known as "8th-day disease," usually due to unsterile umbilical cord cutting.

Q: What is the standard treatment therapy for Pneumocystis jirovecii pneumonia (PCP)?

Co-trimoxazole. **Explanation:** **Pneumocystis jirovecii pneumonia (PCP)** is a life-threatening opportunistic fungal infection primarily seen in immunocompromised individuals, particularly those with HIV/AIDS (CD4 count <200 cells/µL). **1. Why Co-trimoxazole is correct:** Co-trimoxazole (Trimethoprim-Sulfamethoxazole/TMP-SMX) is the **drug of choice** for both the treatment and prophylaxis of PCP [1]. It works by inhibiting sequential steps in the fungal folic acid synthesis pathway. For moderate-to-severe cases, it is administered intravenously; for mild cases, oral administration is sufficient. It has superior efficacy compared to alternative agents like Pentamidine or Atovaquone. **2. Why the other options are incorrect:** * **Ceftriaxone (Option B):** A third-generation cephalosporin used for community-acquired bacterial pneumonia (e.g., *S. pneumoniae*). It has no activity against fungi like *P. jirovecii*. * **Ceftazidime (Option C):** An antipseudomonal third-generation cephalosporin used for hospital-acquired infections. It is ineffective against PCP. * **Amikacin (Option D):** An aminoglycoside antibiotic used for Gram-negative bacterial infections and certain mycobacteria. It does not target fungal pathogens. **High-Yield Clinical Pearls for NEET-PG:** * **Steroid Add-on:** In HIV patients, if the arterial oxygen partial pressure (**PaO2**) is ** 35 mmHg**, systemic corticosteroids (Prednisolone) must be added to Co-trimoxazole to reduce inflammation caused by dying organisms [1]. * **Diagnosis:** The gold standard is identifying the organism via **Gomori Methenamine Silver (GMS)** stain or Direct Fluorescent Antibody (DFA) testing of induced sputum or Bronchoalveolar Lavage (BAL) fluid [1]. * **Radiology:** Classic presentation shows bilateral perihilar "ground-glass" opacities on CXR/HRCT.

Q: Which of the following causes tropical spastic paraplegia?

HTLV-I. ### Explanation **Correct Answer: C. HTLV-I** **Underlying Medical Concept:** Tropical Spastic Paraplegia (TSP), also known as **HTLV-I Associated Myelopathy (HAM)**, is a chronic progressive demyelinating disease of the spinal cord [1]. It is caused by the **Human T-cell Lymphotropic Virus Type I (HTLV-I)**, a retrovirus [1]. The pathogenesis involves a robust immune response against virus-infected T-cells, leading to bystander damage of the spinal cord (primarily the thoracic levels). Clinically, it presents with slowly progressive spastic weakness of the lower limbs, bladder dysfunction, and sensory changes [1]. **Analysis of Incorrect Options:** * **A. EBV (Epstein-Barr Virus):** Primarily associated with Infectious Mononucleosis, Burkitt Lymphoma, Nasopharyngeal Carcinoma, and Oral Hairy Leukoplakia. It does not cause chronic spastic paraplegia. * **B. CMV (Cytomegalovirus):** In immunocompromised patients (like those with AIDS), CMV typically causes retinitis, esophagitis, or polyradiculopathy, but not the specific clinical entity of TSP. * **D. HSV (Herpes Simplex Virus):** HSV-1 is the most common cause of sporadic viral encephalitis, while HSV-2 is associated with aseptic meningitis and Mollaret’s meningitis. **High-Yield Clinical Pearls for NEET-PG:** * **Epidemiology:** TSP/HAM is most common in tropical regions (Caribbean, South America, Africa) and Southern Japan [1]. * **Other HTLV-I Associations:** It is also the causative agent of **Adult T-cell Leukemia/Lymphoma (ATL)**, characterized by "flower cells" on peripheral smear and hypercalcemia [1]. * **Diagnosis:** Detection of HTLV-I antibodies in both serum and CSF (CSF titers are often higher). * **Key Differential:** Always rule out Multiple Sclerosis and spinal cord compression (Pott’s spine) in cases of progressive paraparesis [2].

Q: A 65-year-old man presented with skin lesions six weeks after returning from a vacation in Belize, which included time spent at the beach and in the rainforest. What is the diagnosis?

Bot fly. ***Bot fly*** - **Bot fly myiasis** (Dermatobia hominis) is endemic in **Central America** including Belize, presenting as **boil-like lesions** with a central pore developing weeks after exposure. - The **6-week incubation period** and travel to **rainforest and beach areas** in Belize are classic for bot fly larval development under the skin. *Cutaneous leishmaniasis* - Caused by **Leishmania species** transmitted by **sandflies**, typically presents as **painless ulcers** with raised borders, not boil-like lesions. - More commonly associated with **Mediterranean, Middle Eastern, or South American** regions rather than Belize's specific epidemiology. *Onchocerciasis* - Caused by **Onchocerca volvulus**, transmitted by **blackflies**, primarily presents with **subcutaneous nodules** and **chronic skin changes**. - Endemic in **sub-Saharan Africa** and some parts of Central/South America, but skin lesions develop over **months to years**, not weeks. *Plague* - Caused by **Yersinia pestis**, transmitted by **flea bites** from infected rodents, presents with **painful lymphadenopathy** (bubonic) or systemic illness. - **Acute onset** within days, not weeks, and skin lesions are **eschars** at bite sites, not boil-like lesions.

Question 1

A 30-year-old male with a history of high-grade fever with rigors followed by profuse sweating is admitted to the ICU after an episode of generalized tonic-clonic seizure. The patient was comatose with no focal neurological deficit or signs of meningeal irritation. The eyes were divergent, and the pout reflex was present. What is an important cause of death in this setting?

Accepted Answer

Acidosis

Answer

Aspiration

Answer

Hypoglycemia

Answer

Anemia

Question 2

An 18-year-old woman presents with a 2-day history of sore throat. Which of the following constellation of symptoms and signs is most consistent with group-A streptococcal pharyngitis?

Accepted Answer

Fever, no cough, tonsillar exudates, and tender anterior cervical lymphadenopathy

Answer

Fever, anorexia, dysphagia, and hoarseness

Answer

Fever, runny nose, cough, myalgia, and poor appetite

Answer

Fever, cough, pharyngeal erythema, and dysphagia

Question 3

A 45-year-old woman is undergoing chemotherapy for breast cancer and presents 10 days after her last treatment with fever (temperature >38.5°C) and a sore throat. On examination, she has oral mucositis, and her WBC count is 800/mL with an absolute neutrophil count below 500/mL. Other investigations, including CXR, urinalysis, and biochemistry, are normal. What is the most appropriate next step in management?

Accepted Answer

Start empiric bacterial antibiotics.

Answer

Start empiric antifungal and bacterial antibiotics.

Answer

Administer acetaminophen until culture results are available.

Answer

Start antiviral medications for HSV-1.

Question 4

A 20-year-old woman presents with fever, severe myalgia and arthralgia, pain behind the eyes, and rash for 3 days. Lab reports show thrombocytopenia and leucopenia. What is the most likely diagnosis?

Accepted Answer

Dengue fever

Answer

Malaria

Answer

Typhoid

Answer

Yellow fever

Question 5

What is the most common malignancy in patients with HIV?

Accepted Answer

Lymphoma

Answer

Squamous Cell Carcinoma (SCC)

Answer

Adenocarcinoma

Answer

Fibroma

Question 6

Antiretroviral drugs are started for HIV/AIDS patients if the CD4 count is:

Accepted Answer

Any CD4 count

Answer

< 500 cells/mm

Answer

< 350 cells/mm

Answer

< 200 cells/mm

Question 7

Rigidity of facial muscles, 'Risus sardonicus', is associated with which condition?

Accepted Answer

Tetanus

Answer

Tetany

Answer

Leprosy

Answer

Actinomycosis

Question 8

What is the standard treatment therapy for Pneumocystis jirovecii pneumonia (PCP)?

Accepted Answer

Co-trimoxazole

Answer

Ceftriaxone

Answer

Ceftazidime

Answer

Amikacin

Question 9

Which of the following causes tropical spastic paraplegia?

Accepted Answer

HTLV-I

Answer

EBV

Answer

CMV

Answer

HSV

Question 10

A 65-year-old man presented with skin lesions six weeks after returning from a vacation in Belize, which included time spent at the beach and in the rainforest. What is the diagnosis?

Accepted Answer

Bot fly

Answer

Cutaneous leishmaniasis

Answer

Onchocerciasis

Answer

Plague

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?