Infectious Diseases Practice Questions

Q: Leukopenia is characteristic of which of the following conditions?

Enteric fever. **Explanation:** **Correct Answer: B. Enteric fever** Leukopenia (a decrease in the total white blood cell count) is a classic hematological hallmark of **Enteric Fever (Typhoid)** caused by *Salmonella Typhi* [1]. While most bacterial infections trigger neutrophilic leukocytosis, Enteric fever is a notable exception [1]. The underlying mechanism involves the invasion of the Reticuloendothelial System (RES), specifically the bone marrow, where the bacteria cause marrow suppression and increased destruction of cells. Typically, the WBC count ranges between 3,000 to 5,000/mm³. **Analysis of Incorrect Options:** * **A. Appendicitis:** This is an acute pyogenic inflammatory condition. It characteristically presents with **leukocytosis** (elevated WBC) with a "shift to the left" (increased immature neutrophils), which helps in clinical diagnosis. * **C. Meningitis:** Acute bacterial meningitis typically presents with significant **polymorphonuclear leukocytosis** as the body mounts an immune response against the invading pathogen (e.g., *S. pneumoniae* or *N. meningitidis*). * **D. Myocardial Infarction:** Tissue necrosis in MI triggers a systemic inflammatory response, leading to a transient **leukocytosis** (usually appearing within 24 hours), not leukopenia. **High-Yield Clinical Pearls for NEET-PG:** * **Relative Bradycardia (Faget’s Sign):** Another classic feature of Enteric fever where the pulse rate is slower than expected for the degree of fever [1]. * **Other causes of Leukopenia in Infections:** Viral infections (Influenza, Measles, Hepatitis), Malaria, Kala-azar, and Brucellosis [2]. * **Diagnostic Gold Standard:** Bone marrow culture is the most sensitive test for Enteric fever, especially if antibiotics have already been started. Blood culture is most sensitive in the first week.

Q: Cavitation is most often seen in which type of pneumonia?

Tuberculous pneumonia. **Explanation:** **Correct Answer: B. Tuberculous pneumonia** Cavitation is a hallmark of **Tuberculous pneumonia**, particularly in post-primary (reactivation) tuberculosis [1]. The underlying mechanism is **caseous necrosis**, where a cell-mediated immune response (Type IV hypersensitivity) leads to tissue destruction [1]. When this necrotic material liquefies and drains into the bronchial tree, it leaves behind a gas-filled cavity. These cavities are typically thick-walled and located in the upper lobes (apical/posterior segments) due to higher oxygen tension [1], [4]. **Analysis of Incorrect Options:** * **A. Mycoplasma pneumonia:** Known as "Atypical Pneumonia," it typically presents with interstitial infiltrates and "reticulonodular" patterns. Cavitation is extremely rare. * **C. Streptococcal pneumonia:** *Streptococcus pneumoniae* is the most common cause of community-acquired pneumonia (lobar pattern). It is non-necrotizing; therefore, it rarely causes cavitation or permanent lung scarring [3]. * **D. Staphylococcal pneumonia:** While *Staphylococcus aureus* is a well-known cause of necrotizing pneumonia and can cause **pneumatoceles** (thin-walled, air-filled cysts) or abscesses, it is statistically less frequent than Tuberculosis in the context of chronic cavitary lesions in the Indian subcontinent. **NEET-PG High-Yield Pearls:** * **Most common cause of cavitation globally:** Tuberculosis [1]. * **Most common cause of cavitation in Acute Pneumonia:** *Staphylococcus aureus* and *Klebsiella pneumoniae* (Friedlander’s pneumonia). * **Pneumatoceles:** Characteristically seen in Pediatric Staphylococcal pneumonia. * **Air-fluid levels:** If seen within a cavity, suspect a lung abscess or superinfected TB cavity [2], [4]. * **Bulging Fissure Sign:** Classically associated with *Klebsiella* pneumonia.

Q: What is the causative agent responsible for the chronic carrier state in liver disease?

Hepatitis B virus (HBV). **Explanation:** The chronic carrier state is defined as the persistence of the Hepatitis B surface antigen (**HBsAg**) in the blood for more than **6 months** [1]. Among the options provided, **Hepatitis B Virus (HBV)** is the classic causative agent associated with this state. The risk of becoming a chronic carrier is inversely proportional to the age at infection: approximately 90% of infected neonates become carriers, compared to only 5–10% of immunocompetent adults [1]. **Analysis of Options:** * **Hepatitis A (HAV) & Hepatitis E (HEV):** These are transmitted via the fecal-oral route and cause **acute** hepatitis only [2]. They do not progress to chronic infection or a carrier state (Exception: HEV can cause chronic infection in severely immunocompromised individuals/transplant recipients, but it is not the standard "carrier state" answer). * **Hepatitis C (HCV):** While HCV has a very high rate of **chronicity** (75–85% of cases), the term "chronic carrier state" (asymptomatic persistence with low viral replication) is traditionally and most frequently associated with HBV in medical literature and examinations. **NEET-PG High-Yield Pearls:** * **HBsAg:** First serological marker to appear; indicates active infection (acute or chronic) [1]. * **HBeAg:** Marker of high infectivity and active viral replication. * **Anti-HBs:** Indicates immunity (via recovery or vaccination) [1]. * **Window Period:** The interval when HBsAg disappears but Anti-HBs has not yet appeared; **Anti-HBc IgM** is the only diagnostic marker during this phase [1]. * **Ground-glass hepatocytes:** The characteristic histopathological finding in chronic HBV carriers.

Q: CSF findings show protein 60%, sugar 40%, and neutrophils are predominant. What is the most likely diagnosis?

Bacterial meningitis. **Explanation:** The CSF (Cerebrospinal Fluid) profile provided is characteristic of **Bacterial Meningitis**. In bacterial infections, the inflammatory response is intense, leading to a significant breakdown of the blood-brain barrier and the recruitment of polymorphonuclear leukocytes. * **Why Bacterial Meningitis is correct:** The hallmark findings are **Neutrophilic pleocytosis** (predominance of neutrophils), **elevated protein** (due to increased permeability), and **decreased sugar/glucose** (hypoglycorrhachia). In this case, the sugar is 40% (typically <40-50% of blood glucose), and neutrophils are the dominant cell type, which strongly points to a pyogenic bacterial etiology. **Analysis of Incorrect Options:** * **Viral Meningitis:** Typically presents with **lymphocytic predominance**, normal or slightly elevated protein, and **normal sugar** levels. * **Tuberculous Meningitis (TBM):** While TBM features high protein and low sugar, the cellular response is characteristically **lymphocytic** (chronic inflammation) rather than neutrophilic. * **Fungal Meningitis:** Similar to TBM, it usually presents with a **lymphocytic** picture and low sugar, often seen in immunocompromised patients. **NEET-PG High-Yield Pearls:** 1. **Normal CSF Glucose:** Usually 60-70% of simultaneous blood glucose. 2. **Early Viral Meningitis:** Can rarely show neutrophils in the first 24 hours (neutrophilic shift), but sugar remains normal. 3. **Late Bacterial Meningitis:** If partially treated, the cell type may shift toward lymphocytes, but sugar remains low. 4. **Most common cause (Pediatrics):** *Streptococcus pneumoniae* (overall), *Group B Streptococcus* (neonates).

Q: A 19-year-old male tests positive for hepatitis C infection. He was arrested twice for stealing and belongs to a gang of friends. Which of the following is the most likely method of transmission?

Intravenous drug use. **Explanation:** The correct answer is **D. Intravenous drug use (IVDU).** Hepatitis C Virus (HCV) is primarily a **blood-borne pathogen**. [2] In developed and developing countries alike, the most common risk factor for HCV transmission is the sharing of needles and paraphernalia among intravenous drug users [3]. The clinical vignette provides behavioral clues—history of arrests for theft and gang affiliation—which are high-yield "social markers" in medical exams pointing toward a lifestyle associated with substance abuse and IVDU. **Analysis of Incorrect Options:** * **A. Fecal-oral:** This is the primary route for Hepatitis A and E ("The vowels hit the bowels"). HCV is not transmitted via the fecal-oral route. * **B. Fomite:** HCV is not typically spread through casual contact or inanimate objects (fomites) unless they are contaminated with fresh blood (e.g., shared razors or toothbrushes), but this is significantly less common than IVDU. * **C. Sexual transmission:** While possible, the efficiency of sexual transmission for HCV is remarkably low (unlike HBV or HIV). It is generally only a significant risk factor in individuals with multiple partners or co-infection with HIV. **NEET-PG High-Yield Pearls:** * **Most common cause of post-transfusion hepatitis:** Historically HCV, though now rare due to rigorous screening. * **Chronicity:** HCV has the highest rate of progression to chronic infection (~75–85%) among the hepatitis viruses. * **Screening:** Anti-HCV antibody is the initial screening test; HCV RNA (PCR) is the gold standard for confirming active infection. [1] * **Extrahepatic manifestations:** Essential mixed cryoglobulinemia, Membranoproliferative glomerulonephritis (MPGN), and Porphyria cutanea tarda (PCT).

Q: A 59-year-old man undergoes coronary bypass surgery and receives vancomycin prophylactically for 24 hours. On the ninth postoperative day, he develops a fever of 39.8°C (103°F) with a heart rate of 115 beats/min and a blood pressure of 105/65 mm Hg. The surgical site is healing well with no redness or discharge. His white blood cell count is 14,000/mm³ and urinalysis reveals many white blood cells per high-power field. Blood and urine cultures grow a non-lactose-fermenting oxidase-positive gram-negative rod. Which of the following antibiotics is most appropriate to treat this infection?

Imipenem. ### Explanation **1. Why Imipenem is Correct:** The clinical presentation describes a healthcare-associated infection (likely a UTI/urosepsis) following surgery. The key to the diagnosis lies in the microbiology: a **non-lactose-fermenting, oxidase-positive, Gram-negative rod**. This description is classic for ***Pseudomonas aeruginosa***. Among the options provided, **Imipenem** (a carbapenem) is a potent anti-pseudomonal agent [1]. It is highly effective against multidrug-resistant Gram-negative bacteria often encountered in hospital settings. **2. Why the Other Options are Incorrect:** * **Moxifloxacin (Option A):** While it is a respiratory fluoroquinolone, it lacks reliable activity against *Pseudomonas*. Ciprofloxacin and Levofloxacin are the only fluoroquinolones with anti-pseudomonal activity. * **Ceftriaxone (Option B):** This is a third-generation cephalosporin. While it covers many Gram-negative rods, it has **no activity** against *Pseudomonas*. * **Trimethoprim-sulfamethoxazole (Option D):** This is typically used for uncomplicated UTIs or specific organisms like *Stenotrophomonas*, but it is not effective against *Pseudomonas*. **3. Clinical Pearls for NEET-PG:** * **Pseudomonas Identification:** Gram-negative rod, Oxidase positive, Non-lactose fermenter (NLF), produces pigments (Pyocyanin/Pyoverdin), and has a characteristic "fruity/grape-like" odor. * **Anti-pseudomonal "Must-Knows":** * **Penicillins:** Piperacillin-Tazobactam (Pip-Tazo). * **Cephalosporins:** Ceftazidime (3rd gen), Cefepime (4th gen). * **Carbapenems:** Imipenem, Meropenem (**Note:** *Ertapenem* does NOT cover Pseudomonas). * **Fluoroquinolones:** Ciprofloxacin, Levofloxacin. * **Monobactams:** Aztreonam. * **Aminoglycosides:** Amikacin, Gentamicin, Tobramycin.

Q: What is the recommended duration for isolation of a patient with bacterial meningitis?

24 hours after the start of antibiotic treatment. **Explanation:** In cases of bacterial meningitis, particularly those caused by *Neisseria meningitidis* and *Haemophilus influenzae* type b, the primary goal of isolation is to prevent droplet transmission. The correct answer is **24 hours after the start of effective antibiotic treatment** because most pathogenic bacteria are rapidly cleared from the nasopharynx within this timeframe. Once therapeutic levels of antibiotics (such as Ceftriaxone) are achieved, the patient is no longer considered contagious to others. **Analysis of Options:** * **Option A:** Waiting for a negative culture is impractical and unnecessary. Cultures can take 48–72 hours, and patients are typically non-infectious long before results are finalized. * **Option C & D:** Clinical markers like fever subsidence or resolution of neck rigidity are indicators of clinical recovery, not infectivity. A patient may remain symptomatic for several days despite being bacteriologically sterile and non-contagious. **High-Yield Clinical Pearls for NEET-PG:** * **Type of Isolation:** **Droplet Precautions** are mandatory for *N. meningitidis* and *H. influenzae*. For other causes like *S. pneumoniae*, standard precautions usually suffice, but 24-hour isolation is a safe general rule in clinical practice. * **Chemoprophylaxis:** Close contacts of patients with Meningococcal meningitis should receive prophylaxis (Rifampicin, Ciprofloxacin, or Ceftriaxone) as soon as possible. * **Steroids:** Dexamethasone should be administered **before or with the first dose** of antibiotics to reduce the risk of sensorineural hearing loss, especially in *H. influenzae* meningitis.

Q: A farmer who handles goats and sheep is presenting with fever, muscle and joint pain, and rash. What is the most likely diagnosis?

Brucellosis. **Explanation:** **Brucellosis** is the most likely diagnosis given the patient's occupation and clinical presentation. It is a classic zoonotic infection transmitted to humans through direct contact with infected animals (goats, sheep, cattle, pigs) or by consuming unpasteurized dairy products. 1. **Why Brucellosis is correct:** The triad of **occupational exposure** (farming goats/sheep), **constitutional symptoms** (fever, arthralgia, myalgia), and a **rash** (though less common than fever, it can occur) points strongly toward *Brucella melitensis* (common in goats/sheep) [1]. The fever is often "undulant" (rising and falling like waves). 2. **Why other options are incorrect:** * **Melioidosis:** Caused by *Burkholderia pseudomallei*, it is typically associated with exposure to **soil and surface water** (e.g., rice farmers), not specifically goats or sheep. It often presents with pulmonary involvement or abscesses. * **Malaria:** While it causes fever and body aches, it is transmitted by the *Anopheles* mosquito. It lacks a specific association with livestock handling. * **Glanders:** Caused by *Burkholderia mallei*, this is primarily a disease of **horses, donkeys, and mules**. While it is zoonotic, the specific mention of goats and sheep makes Brucellosis the superior choice. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Bone marrow culture (more sensitive than blood culture) [1]. * **Standard Serology:** Standard Agglutination Test (SAT); titers >1:160 are significant [1]. * **Treatment:** WHO recommends **Rifampicin + Doxycycline** for 6 weeks [1]. For complications like spondylitis or endocarditis, Streptomycin is often added. * **Key Association:** Look for "Undulant fever" and "Malta fever" in clinical vignettes.

Q: What is the best treatment for a diabetic patient with the condition described below?

Amphotericin. ***Correct Answer: Amphotericin B*** The image shows **rhinocerebral mucormycosis** — a life-threatening fungal infection caused by *Mucor*, *Rhizopus*, or *Rhizomucor* species, seen characteristically in **poorly controlled diabetic patients** (especially those in diabetic ketoacidosis). **Key clinical features:** - **Black necrotic eschar** on nasal mucosa, hard palate, or periorbital region - Rapid spread to sinuses, orbit, and brain - Strongly associated with **diabetes mellitus** (high glucose + acidosis impairs phagocyte function) **Why Amphotericin B is correct:** - **Drug of choice** for mucormycosis - Liposomal Amphotericin B (L-AmB) is preferred for lower nephrotoxicity - Mucorales are **intrinsically resistant** to azole antifungals (including ketoconazole, fluconazole, voriconazole) *Incorrect: Ketoconazole* - An azole antifungal — **not effective** against Mucorales due to intrinsic azole resistance - Would be appropriate for dermatophytosis or candidiasis, not mucormycosis *Incorrect: Ceftriaxone* - A 3rd-generation cephalosporin (antibiotic) — **no antifungal activity** - Irrelevant for this fungal infection *Incorrect: Vancomycin* - A glycopeptide antibiotic active against Gram-positive bacteria (MRSA, etc.) — **no antifungal activity** - Completely ineffective against Mucorales **Key mnemonic:** "Mucor = Must use Amphotericin — azoles fail!"

Q: Which of the following is the most effective treatment of severe malaria?

Artemisinin-based combination therapy. **Explanation:** The management of malaria is a high-yield topic for NEET-PG. According to the latest WHO and National Vector Borne Disease Control Programme (NVBDCP) guidelines, **Artemisinin-based Combination Therapy (ACT)** is the treatment of choice for severe malaria and uncomplicated *P. falciparum* malaria. **Why ACT is Correct:** Artemisinin derivatives (like Artesunate or Artemether) are the most potent antimalarials. They produce a rapid reduction in parasite biomass and quick clinical resolution. In **severe malaria**, the standard of care is **Intravenous (IV) Artesunate** for at least 24 hours, followed by a full oral course of ACT [1]. ACTs combine a fast-acting artemisinin with a long-acting partner drug (e.g., Lumefantrine, Piperaquine) to ensure complete clearance of remaining parasites and prevent resistance. **Why Other Options are Incorrect:** * **Chloroquine:** Once the gold standard, it is now largely ineffective against *P. falciparum* due to widespread resistance. It remains the drug of choice only for sensitive *P. vivax* cases. * **Primaquine:** This is used primarily for its **gametocidal** action (to prevent transmission) and for **radical cure** (to kill hypnozoites in the liver) in *P. vivax* and *P. ovale*. It is not used as a primary treatment for acute severe malaria. * **Doxycycline:** This is a slow-acting antimalarial used as an adjunct to Quinine or for prophylaxis. It is never used as monotherapy for severe malaria. **High-Yield Clinical Pearls:** * **Drug of Choice for Severe Malaria:** IV Artesunate (preferred over Quinine due to lower risk of hypoglycemia) [1]. * **ACT in Pregnancy:** ACT is now recommended for *P. falciparum* in **all trimesters**, including the first. * **Blackwater Fever:** A complication of *P. falciparum* (and historically Quinine use) characterized by massive intravascular hemolysis and hemoglobinuria.

Question 1

Leukopenia is characteristic of which of the following conditions?

Accepted Answer

Enteric fever

Answer

Appendicitis

Answer

Meningitis

Answer

Myocardial infarction

Question 2

Cavitation is most often seen in which type of pneumonia?

Accepted Answer

Tuberculous pneumonia

Answer

Mycoplasma pneumonia

Answer

Streptococcal pneumonia

Answer

Staphylococcal pneumonia

Question 3

What is the causative agent responsible for the chronic carrier state in liver disease?

Accepted Answer

Hepatitis B virus (HBV)

Answer

Hepatitis A virus (HAV)

Answer

Hepatitis E virus (HEV)

Answer

Hepatitis C virus (HCV)

Question 4

CSF findings show protein 60%, sugar 40%, and neutrophils are predominant. What is the most likely diagnosis?

Accepted Answer

Bacterial meningitis

Answer

Viral meningitis

Answer

Tuberculous meningitis

Answer

Fungal meningitis

Question 5

A 19-year-old male tests positive for hepatitis C infection. He was arrested twice for stealing and belongs to a gang of friends. Which of the following is the most likely method of transmission?

Accepted Answer

Intravenous drug use

Answer

Fecal-oral

Answer

Fomite

Answer

Sexual transmission

Question 6

A 59-year-old man undergoes coronary bypass surgery and receives vancomycin prophylactically for 24 hours. On the ninth postoperative day, he develops a fever of 39.8°C (103°F) with a heart rate of 115 beats/min and a blood pressure of 105/65 mm Hg. The surgical site is healing well with no redness or discharge. His white blood cell count is 14,000/mm³ and urinalysis reveals many white blood cells per high-power field. Blood and urine cultures grow a non-lactose-fermenting oxidase-positive gram-negative rod. Which of the following antibiotics is most appropriate to treat this infection?

Accepted Answer

Imipenem

Answer

Moxifloxacin

Answer

Ceftriaxone

Answer

Trimethoprim-sulfamethoxazole

Question 7

What is the recommended duration for isolation of a patient with bacterial meningitis?

Accepted Answer

24 hours after the start of antibiotic treatment

Answer

Until the bacterial culture is negative

Answer

7 days after the subsidence of fever

Answer

3 days after the resolution of neck rigidity

Question 8

A farmer who handles goats and sheep is presenting with fever, muscle and joint pain, and rash. What is the most likely diagnosis?

Accepted Answer

Brucellosis

Answer

Melioidosis

Answer

Malaria

Answer

Glanders

Question 9

What is the best treatment for a diabetic patient with the condition described below?

Accepted Answer

Amphotericin

Answer

Ceftriaxone

Answer

Vancomycin

Answer

Ketoconazole

Question 10

Which of the following is the most effective treatment of severe malaria?

Accepted Answer

Artemisinin-based combination therapy

Answer

Chloroquine

Answer

Primaquine

Answer

Doxycycline

Infectious Diseases — MCQs

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