Infectious Diseases Practice Questions

Q: Prodromal symptom complex of tetanus consists of which of the following?

All the above. Tetanus is caused by the neurotoxin **tetanospasmin**, produced by *Clostridium tetani*. The clinical presentation typically follows an incubation period (usually 3–21 days) and begins with a non-specific prodromal phase before the onset of classic generalized muscle spasms [1]. 1. **Restlessness and Irritability:** These are among the earliest signs of autonomic nervous system involvement and neuromuscular irritability. Patients often feel an unexplained sense of unease or anxiety. 2. **Headache:** This is a common early constitutional symptom. Along with low-grade fever and malaise, it reflects the initial systemic response to the toxin. 3. **Masseter Muscle Spasm (Trismus):** While trismus is the hallmark of "Lockjaw," it often begins as a subtle stiffness or mild spasm of the masseter muscles during the prodromal phase before progressing to full-blown rigidity. Since all three symptoms—restlessness, headache, and early masseter involvement—characterize the transition from the incubation period to the clinical disease, **Option D (All the above)** is the correct choice. **High-Yield Clinical Pearls for NEET-PG:** * **Descending Paralysis:** Tetanus typically follows a descending pattern: Trismus (Lockjaw) → Risus Sardonicus (facial grin) → Opisthotonus (archback) → Respiratory failure. * **Diagnosis:** It is a **clinical diagnosis**. Laboratory tests (like wound cultures) are often negative and not required for treatment. * **Spatula Test:** A high-yield bedside test where touching the oropharynx triggers a reflex bite (positive) instead of a gag reflex (negative). * **Management:** The priority is neutralizing unbound toxin with **Human Tetanus Immune Globulin (HTIG)** and controlling spasms with benzodiazepines.

Q: A 26-year-old patient presents with suspected pneumococcal meningitis. CSF culture is sent for antibiotic sensitivity. Which empirical antibiotic should be given until culture sensitivity results are available?

Cefotaxime + vancomycin. **Explanation:** The management of bacterial meningitis is a medical emergency requiring immediate empirical antibiotic therapy. The choice of drugs is guided by the most likely pathogens and current resistance patterns. [2] **1. Why Option D is Correct:** * **Streptococcus pneumoniae** is the most common cause of community-acquired bacterial meningitis in adults. [1] * Due to the rising prevalence of **penicillin-resistant** and **cephalosporin-resistant** pneumococci, monotherapy with a third-generation cephalosporin (Cefotaxime or Ceftriaxone) is no longer sufficient. * **Vancomycin** is added empirically to ensure coverage against these highly resistant strains. Once culture sensitivity results are available, the regimen can be narrowed. **2. Why Other Options are Incorrect:** * **Option A (Penicillin G):** While historically the drug of choice, it is no longer used empirically due to widespread high-level penicillin resistance in *S. pneumoniae*. * **Option B (Ceftriaxone + Metronidazole):** Ceftriaxone is appropriate, but Metronidazole is used for anaerobic coverage (e.g., brain abscesses) and has no role in the standard empirical treatment of community-acquired pneumococcal meningitis. [3] * **Option C (Doxycycline):** This is a bacteriostatic drug with poor CNS penetration and is not indicated for the treatment of acute bacterial meningitis. **Clinical Pearls for NEET-PG:** * **Steroids:** Dexamethasone should be administered **before or with** the first dose of antibiotics to reduce neurological complications (hearing loss, edema). [1] * **Age-specific coverage:** In patients >50 years or those who are immunocompromised, **Ampicillin** must be added to the regimen to cover *Listeria monocytogenes*. * **CSF Findings:** Classic bacterial meningitis shows high opening pressure, high protein (>45 mg/dL), low glucose (<40 mg/dL), and neutrophilic pleocytosis. [1]

Q: Hepatitis C is associated with all of the following except:

Dermatomyositis-like syndrome. **Explanation:** Hepatitis C Virus (HCV) is a systemic infection known for its numerous extrahepatic manifestations, primarily mediated by immune complex deposition and chronic immune activation. **Why Dermatomyositis-like syndrome is the correct answer:** Dermatomyositis-like syndrome is classically associated with **Hepatitis B Virus (HBV)** and certain malignancies, but it is not a recognized association of Hepatitis C. While HCV can cause various skin and muscle symptoms, it does not typically present with the specific inflammatory myopathy and heliotrope rash characteristic of dermatomyositis. **Analysis of other options:** * **Polyarteritis nodosa (PAN):** While PAN is most famously associated with Hepatitis B (up to 30% of cases), it is also documented in patients with **Hepatitis C** [1]. However, HCV is more strongly linked to **Mixed Cryoglobulinemia (Type II)**, which presents as a small-vessel vasculitis. * **Lichen planus:** There is a statistically significant correlation between HCV infection and Lichen planus (especially the oral form). It is a high-yield association frequently tested in postgraduate exams. **High-Yield Clinical Pearls for NEET-PG:** * **Most common HCV association:** Mixed Cryoglobulinemia (presents with Meltzer’s triad: purpura, arthralgia, and weakness). * **Renal association:** Membranoproliferative glomerulonephritis (MPGN). * **Dermatological associations:** Porphyria cutanea tarda (PCT) and Lichen planus. * **Endocrine association:** Type 2 Diabetes Mellitus and Autoimmune Thyroiditis [2]. * **B-cell Lymphoma:** Chronic HCV stimulation can lead to Non-Hodgkin Lymphoma.

Q: A 10-year-old school girl has recurrent episodes of boils on the scalp. The boils subside with antibiotic therapy but recur after some time. What is the most likely cause of these recurrences?

Pediculosis capitis. **Explanation:** The clinical presentation of recurrent boils (furunculosis) on the scalp of a school-going girl, which respond to antibiotics but recur shortly after, is a classic sign of an underlying **predisposing factor** rather than a primary infectious failure [1]. **Why Pediculosis Capitis is the correct answer:** Pediculosis capitis (head lice) is the most common cause of recurrent scalp pyoderma in school-aged children. The lice cause intense pruritus; subsequent scratching leads to **micro-abrasions and skin breaches**. These breaches serve as a portal of entry for commensal bacteria like *Staphylococcus aureus*, leading to secondary bacterial infections (boils/impetigo) [1]. While antibiotics clear the current infection, they do not eliminate the lice. The persistent itching and scratching cycle leads to inevitable recurrence. **Analysis of Incorrect Options:** * **Primary Immunodeficiency:** While these can cause recurrent infections, they typically present with systemic involvements (pneumonia, abscesses in deep organs, or failure to thrive) rather than localized scalp boils alone. * **Juvenile Diabetes Mellitus:** Poor glycemic control predisposes to skin infections, but it is a less common cause in this specific age group compared to the high prevalence of head lice in schools. It would usually present with systemic symptoms like polyuria or weight loss. * **HPV Infection:** Human Papillomavirus causes warts (verrucae), not acute inflammatory boils or furuncles. **NEET-PG Clinical Pearls:** * In any case of **recurrent pyoderma** in children, always look for an underlying itchy dermatosis (Lice, Scabies, or Atopic Dermatitis) [1]. * **Occipital lymphadenopathy** is a common physical finding associated with secondary infection in pediculosis capitis. * The drug of choice for Pediculosis capitis is **Topical Permethrin (1%)**; alternatively, Ivermectin can be used.

Q: All are true about post-meningococcal reactive disease, EXCEPT?

Develops after 4 weeks of meningococcal disease. ### Explanation **Post-meningococcal Reactive Disease (PMRD)** is an immune-mediated phenomenon that occurs during the recovery phase of meningococcal meningitis. **1. Why Option A is the Correct Answer (The "Except"):** The timing in Option A is incorrect. PMRD typically develops **4 to 10 days** after the onset of the initial meningococcal illness, not 4 weeks. It is characterized by an immune-complex mediated (Type III hypersensitivity) reaction as the patient is recovering from the acute infection. **2. Analysis of Other Options:** * **Option B:** The clinical triad of PMRD includes **arthritis** (most common), **maculopapular or vasculitic rash**, and **polyserositis** (such as pleurisy or pericarditis). Fever often recurs during this phase. * **Option C:** The condition is self-limiting. These immune-mediated features **resolve spontaneously** within 1 to 2 weeks without causing permanent joint damage or long-term sequelae. * **Option D:** Since PMRD is an **immunological reaction** and not a relapse of the bacterial infection, additional or prolonged antibiotic prophylaxis is not indicated. Treatment is primarily supportive, using NSAIDs for pain and inflammation. **Clinical Pearls for NEET-PG:** * **Pathogenesis:** It is caused by the deposition of circulating immune complexes (meningococcal antigen + antibody) in synovial tissues and blood vessels. * **Synovial Fluid:** If joints are aspirated, the fluid is usually sterile (culture negative) with a high polymorphonuclear leukocyte count. * **Differential Diagnosis:** It must be distinguished from a treatment failure or secondary infection; however, the patient with PMRD usually appears clinically stable despite the new-onset fever and joint pain.

Q: Antibiotic-associated diarrhea is most commonly caused by which organism?

Clostridioides difficile. **Explanation:** **1. Why Clostridioides difficile is correct:** *Clostridioides difficile* (formerly *Clostridium*) is the most common identifiable cause of antibiotic-associated diarrhea (AAD) [1]. The underlying mechanism involves the disruption of normal colonic flora by broad-spectrum antibiotics (most commonly Clindamycin, Fluoroquinolones, and Cephalosporins). This allows *C. difficile* to colonize the gut and release **Toxin A (Enterotoxin)** and **Toxin B (Cytotoxin)**, leading to mucosal inflammation and, in severe cases, the formation of yellow-white plaques known as **Pseudomembranous colitis** [1]. **2. Why the other options are incorrect:** * **Vibrio cholerae:** Causes "rice-water" stools through a toxin-mediated mechanism (adenylate cyclase activation) but is associated with contaminated water/food, not antibiotic use. * **Salmonella species:** Typically causes food poisoning or enteric fever. While it causes diarrhea, it is not a sequela of antibiotic-induced flora disruption. * **Klebsiella pneumoniae:** While *K. oxytoca* is specifically linked to antibiotic-associated hemorrhagic colitis, *K. pneumoniae* is primarily a respiratory and urinary pathogen and is not the "most common" cause of AAD. **3. NEET-PG High-Yield Pearls:** * **Drug of Choice:** Oral **Vancomycin** or **Fidaxomicin** are first-line treatments. Metronidazole is now reserved for non-severe cases if other options are unavailable. * **Diagnosis:** The gold standard for toxin identification is the **Cell Cytotoxicity Assay**, but the most common initial tests are **GDH (Glutamate Dehydrogenase) screening** and **NAAT/PCR** for toxin genes [1]. * **Risk Factors:** Advanced age, prolonged hospitalization, and use of **Proton Pump Inhibitors (PPIs)** [1]. * **Alcohol-based rubs** are ineffective against *C. difficile* spores; handwashing with soap and water is mandatory.

Q: A 62-year-old man presents with new symptoms of fevers, chills, and malaise. His past medical history is significant for a prosthetic aortic valve replacement 5 years ago due to aortic stenosis from a bicuspid valve. On physical examination, the blood pressure is 130/85 mm Hg, heart rate is 88/min, and temperature is 38.5°C. He has a 2/6 systolic ejection murmur heard best at the aortic region and a mechanical second heart sound, but no other abnormalities on examination. Blood cultures are most likely to grow which of the following organisms?

Staphylococcus epidermidis. The patient presents with symptoms of **Prosthetic Valve Endocarditis (PVE)**. The key to identifying the causative organism in PVE is the **timing** of symptom onset after surgery. 1. **Why D is correct:** PVE is classified into early ( 1 year) onset [1]. While **Staphylococcus epidermidis** (Coagulase-negative Staphylococci) is the most common cause of *early* PVE due to perioperative contamination, it remains a significant pathogen in late PVE as well. However, in the context of NEET-PG questions, if a patient has a prosthetic valve and the clinical picture suggests endocarditis, **Staphylococci** (specifically *S. epidermidis*) are the most frequently implicated organisms across various stages of the disease due to their ability to form biofilms on prosthetic material [1]. 2. **Why other options are incorrect:** * **A & B (Fungi/Bartonella):** These are causes of "Culture-Negative Endocarditis." While they occur, they are far less common than bacterial causes. * **C (Diphtheroids):** *Corynebacterium* species are rare causes of PVE and are usually considered contaminants unless isolated from multiple blood cultures. **Clinical Pearls for NEET-PG:** * **Early PVE ( 12 months):** The microbiology starts to resemble Native Valve Endocarditis (NVE) [4], with *Streptococcus* species and *Staphylococcus aureus* becoming more prevalent. However, *S. epidermidis* remains a high-yield answer for any prosthetic material infection. * **Duke’s Criteria:** Remember that a new valvular regurgitation or positive blood cultures are "Major Criteria" for diagnosis [2]. * **Treatment:** PVE caused by *S. epidermidis* usually requires a combination of Vancomycin + Rifampin + Gentamicin [3].

Question 1

Prodromal symptom complex of tetanus consists of which of the following?

Accepted Answer

All the above

Answer

Restlessness

Answer

Headache

Answer

Masseter muscle spasm

Question 2

A 26-year-old patient presents with suspected pneumococcal meningitis. CSF culture is sent for antibiotic sensitivity. Which empirical antibiotic should be given until culture sensitivity results are available?

Accepted Answer

Cefotaxime + vancomycin

Answer

Penicillin G

Answer

Ceftriaxone + metronidazole

Answer

Doxycycline

Question 3

Hepatitis C is associated with all of the following except:

Accepted Answer

Dermatomyositis-like syndrome

Answer

Polyarteritis nodosa (PAN)

Answer

Lichen planus

Answer

All of the above

Question 4

A 10-year-old school girl has recurrent episodes of boils on the scalp. The boils subside with antibiotic therapy but recur after some time. What is the most likely cause of these recurrences?

Accepted Answer

Pediculosis capitis

Answer

Primary immunodeficiency syndrome

Answer

Juvenile diabetes mellitus

Answer

HPV infection

Question 5

All are true about post-meningococcal reactive disease, EXCEPT?

Accepted Answer

Develops after 4 weeks of meningococcal disease

Answer

Maculopapular or vasculitic rash and polyserositis

Answer

These features resolve spontaneously without sequelae

Answer

Antibiotic prophylaxis is not needed

Question 6

Relapse in malaria is seen in which Plasmodium species?

Accepted Answer

P. vivax, P. ovale, and P. malariae

Answer

P. malariae and P. ovale

Answer

P. vivax and P. malariae

Answer

P. falciparum and P. ovale

Question 7

A 49-year-old gentleman undergoes a root canal procedure. A few days later, he develops fever, weight loss, and anorexia. He is diagnosed with mitral valve prolapse with mitral regurgitation. What is the most common organism implicated in the causation of this condition?

Accepted Answer

Viridans streptococci

Answer

Streptococcus pneumoniae

Answer

Staphylococcus aureus

Answer

Providencia stuartii

Question 8

Which of the following statements regarding diarrhea in HIV infection is incorrect?

Accepted Answer

Mycobacterium avium complex may cause diarrhea due to malabsorption, which responds well to treatment.

Answer

Diarrhea due to Salmonella has a greater incidence of associated bacteremia and may require chronic suppressive antibiotic therapy.

Answer

The most common parasites associated with diarrhea in HIV infection are Giardia lamblia, Entamoeba histolytica, and Cryptosporidium.

Answer

Cryptosporidium is diagnosed by acid-fast stain of intestinal biopsy or stool specimens, and there is no proven effective treatment.

Question 9

Antibiotic-associated diarrhea is most commonly caused by which organism?

Accepted Answer

Clostridioides difficile

Answer

Vibrio cholerae

Answer

Salmonella species

Answer

Klebsiella pneumoniae

Question 10

A 62-year-old man presents with new symptoms of fevers, chills, and malaise. His past medical history is significant for a prosthetic aortic valve replacement 5 years ago due to aortic stenosis from a bicuspid valve. On physical examination, the blood pressure is 130/85 mm Hg, heart rate is 88/min, and temperature is 38.5°C. He has a 2/6 systolic ejection murmur heard best at the aortic region and a mechanical second heart sound, but no other abnormalities on examination. Blood cultures are most likely to grow which of the following organisms?

Accepted Answer

Staphylococcus epidermidis

Answer

Fungi

Answer

Bartonella

Answer

Diphtheroids

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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