Infectious Diseases — MCQs
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Which of the following is the drug of first choice for Non-Gonococcal Urethritis?
A 26-year-old woman presents with fever, malaise, and jaundice. She denies alcohol abuse but reports consuming raw oysters 3 weeks prior. Physical examination reveals scleral icterus, a mildly enlarged and tender liver. Laboratory studies show markedly increased AST and ALT, and increased IgM and anti-HAV titers. What is the most likely outcome of this infection?
Which of the following statements is true about HIV?
What is the most common cause of acute bacterial endocarditis?
Typhoid intestinal perforation usually occurs in which week of typhoid fever?
Which of the following statements regarding Candida is true?
What is the most common ocular infection following renal transplantation?
A 24-year-old female presented to the ER with a characteristic rash and fever. On examination, a chronic lower extremity ulcer related to prior trauma, hypotension, and tachycardia were noted. Diffuse erythema was prominent on palms, conjunctiva, and oral mucosa. Lab findings revealed deranged RFTs, moderately increased SGOT and SGPT, and mild thrombocytopenia. The patient was resuscitated with IV fluid and vasopressors. Blood cultures were negative after 72 hours, and the patient's fingers started to desquamate. Which of the organisms is the most likely cause of the above condition?
What is the drug of choice in a patient with severe complicated falciparum malaria?
Which of the following tests specifically detects Plasmodium falciparum?
Infectious Diseases Indian Medical PG Practice Questions and MCQs
Question 271: Which of the following is the drug of first choice for Non-Gonococcal Urethritis?
- A. Ceftriaxone
- B. Ciprofloxacin
- C. Doxycycline (Correct Answer)
- D. Minocycline
Explanation: **Explanation:** **Non-Gonococcal Urethritis (NGU)** is most commonly caused by *Chlamydia trachomatis* (30-50% of cases), followed by *Mycoplasma genitalium* and *Ureaplasma urealyticum* [1]. 1. **Why Doxycycline is the Correct Choice:** According to the latest CDC and WHO guidelines, **Doxycycline (100 mg twice daily for 7 days)** is the first-line treatment for NGU. It has superior efficacy in eradicating *Chlamydia* and is more effective than a single dose of Azithromycin for rectal infections and *Mycoplasma genitalium* (though resistance is rising). Doxycycline works by inhibiting protein synthesis (30S subunit), providing excellent coverage against the atypical bacteria responsible for NGU. 2. **Why Other Options are Incorrect:** * **Ceftriaxone:** This is a third-generation cephalosporin and the drug of choice for **Gonococcal Urethritis** (Gonorrhea) [1]. It is ineffective against cell-wall-deficient organisms like *Chlamydia*. * **Ciprofloxacin:** While a fluoroquinolone, it is no longer recommended as first-line due to high rates of resistance in *Neisseria gonorrhoeae* and suboptimal efficacy against *Chlamydia*. * **Minocycline:** Although effective against some strains of *Chlamydia*, it is not the standard of care or the "first choice" compared to the established profile of Doxycycline. **High-Yield Clinical Pearls for NEET-PG:** * **Syndromic Management (NACO):** In India, NGU is managed under **Kit 2 (Green)**, which contains Secnidazole (2g single dose) and Fluconazole (150mg). However, for specific bacterial NGU, Doxycycline is the gold standard. * **Co-infection:** Patients with Gonorrhea are often co-infected with Chlamydia; hence, treatment usually combines Ceftriaxone (IM) + Doxycycline (Oral). * **Persistent NGU:** If symptoms persist after Doxycycline, suspect *Trichomonas vaginalis* or *Mycoplasma genitalium* resistance; consider Metronidazole or Moxifloxacin.
Question 272: A 26-year-old woman presents with fever, malaise, and jaundice. She denies alcohol abuse but reports consuming raw oysters 3 weeks prior. Physical examination reveals scleral icterus, a mildly enlarged and tender liver. Laboratory studies show markedly increased AST and ALT, and increased IgM and anti-HAV titers. What is the most likely outcome of this infection?
- A. Cirrhosis
- B. Complete resolution (Correct Answer)
- C. Establishment of a chronic carrier state
- D. Fulminant hepatitis
Explanation: ### Explanation **Correct Answer: B. Complete resolution** The clinical presentation (fever, jaundice, tender hepatomegaly) and laboratory findings (markedly elevated transaminases and **IgM anti-HAV**) confirm a diagnosis of **Acute Hepatitis A Virus (HAV)** infection [1]. The history of raw oyster consumption is a classic risk factor for HAV, which is transmitted via the fecal-oral route. Symptoms such as tender liver and dark urine are characteristic, typically lasting 3–6 weeks [1]. **Why Complete Resolution is Correct:** Hepatitis A is a self-limiting disease. Unlike Hepatitis B or C, **HAV does not cause chronic infection, a chronic carrier state, or cirrhosis.** In over 99% of cases, especially in young, immunocompetent patients, the infection resolves completely within weeks to months with supportive care, leading to lifelong immunity (marked by IgG anti-HAV) [3]. **Analysis of Incorrect Options:** * **A & C (Cirrhosis & Chronic carrier state):** These are complications associated with Hepatitis B, C, and D [2]. HAV and HEV (except in immunocompromised HEV cases) do not progress to chronicity or permanent liver scarring (cirrhosis). * **D (Fulminant hepatitis):** While HAV can cause acute liver failure (fulminant hepatitis), it occurs in less than 1% of cases [1]. Given the patient's age and typical presentation, complete resolution is the statistically "most likely" outcome. --- ### NEET-PG High-Yield Pearls * **Transmission:** Fecal-oral route; often associated with contaminated water or shellfish (oysters). * **Serology:** * **IgM anti-HAV:** Gold standard for diagnosing **acute** infection [3]. * **IgG anti-HAV:** Indicates **past** infection or vaccination; provides lifelong protection [3]. * **Incubation Period:** Approximately 2–6 weeks (Average: 4 weeks). * **Extra-hepatic manifestation:** Most common is evanescent rash or arthralgia; rarely, cholestatic hepatitis. * **Vaccination:** Killed vaccine is part of the recommended schedule for high-risk groups [3].
Question 273: Which of the following statements is true about HIV?
- A. HIV is not transmitted through semen.
- B. There are more chances of HIV transmission during LSCS than normal labor.
- C. HIV is more infectious than hepatitis B.
- D. Male-to-female transmission of HIV is higher than female-to-male transmission. (Correct Answer)
Explanation: ### Explanation **Correct Option: D. Male-to-female transmission of HIV is higher than female-to-male transmission.** The transmission efficiency of HIV during heterosexual vaginal intercourse is significantly higher from male to female (approximately 0.08% per act) than from female to male (approximately 0.04% per act). This is due to biological factors: a larger surface area of the vaginal and cervical mucosa is exposed to infected semen, and semen typically contains a higher concentration of the virus than vaginal secretions [1]. Additionally, semen remains in the vaginal vault for a prolonged period, increasing exposure time. **Analysis of Incorrect Options:** * **A. HIV is not transmitted through semen:** This is incorrect. Semen is one of the primary vehicles for HIV transmission, containing both free virus particles and infected mononuclear cells [1]. * **B. There are more chances of HIV transmission during LSCS than normal labor:** This is incorrect. Elective Lower Segment Cesarean Section (LSCS) before the onset of labor or rupture of membranes actually **reduces** the risk of vertical transmission compared to vaginal delivery, as it avoids contact with infected birth canal secretions and blood [1]. * **C. HIV is more infectious than hepatitis B:** This is incorrect. Hepatitis B Virus (HBV) is significantly more infectious than HIV. The risk of transmission after a needle-stick injury from an infected source is approximately **0.3% for HIV**, whereas it ranges from **6% to 30% for HBV**. **High-Yield Clinical Pearls for NEET-PG:** * **Post-Exposure Prophylaxis (PEP):** Must be started within 72 hours (ideally within 2 hours) and continued for 28 days. * **Vertical Transmission:** The most common time for mother-to-child transmission is **during delivery** (intrapartum). * **Transmission Risk:** Receptive anal intercourse carries the highest risk among sexual acts (~1.38%). * **Window Period:** The time between infection and the detectability of antibodies (usually 3–12 weeks). p24 antigen is the earliest marker detectable by ELISA.
Question 274: What is the most common cause of acute bacterial endocarditis?
- A. Staphylococcus aureus (Correct Answer)
- B. Streptococcus viridans
- C. Streptococcus intermedius
- D. Candida albicans
Explanation: **Explanation:** Infective Endocarditis (IE) is clinically classified into two types: Acute and Subacute. The distinction is based on the virulence of the organism and the clinical progression [1]. **1. Why Staphylococcus aureus is correct:** *Staphylococcus aureus* is a highly virulent organism and is the **most common cause of Acute Bacterial Endocarditis** [1]. It typically affects previously healthy (native) heart valves, leading to rapid valvular destruction, high-grade fever, and frequent embolic complications [1][2]. It is also the most common cause of IE in intravenous drug users (IVDUs), where it frequently involves the tricuspid valve [1]. **2. Why the other options are incorrect:** * **Streptococcus viridans:** This is the most common cause of **Subacute Bacterial Endocarditis (SBE)**. It has low virulence and typically affects valves that are already damaged (e.g., by rheumatic heart disease or congenital defects) [1]. * **Streptococcus intermedius:** This belongs to the *S. anginosus* group. While it can cause endocarditis, it is more characteristically associated with the formation of visceral abscesses (brain, liver, or spleen). * **Candida albicans:** This is a fungal cause of endocarditis. It is rare and usually seen in specific high-risk groups such as immunocompromised patients, those on long-term TPN, or post-cardiac surgery. It is characterized by large, friable vegetations. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause overall:** *S. aureus* (has overtaken *S. viridans* in recent years) [1]. * **Most common cause in IVDUs:** *S. aureus* (Tricuspid valve) [1]. * **Early Prosthetic Valve Endocarditis (<1 year):** *Staphylococcus epidermidis* [3]. * **Late Prosthetic Valve Endocarditis (>1 year):** *Streptococcus viridans*. * **Culture-negative Endocarditis:** Most commonly due to prior antibiotic use or HACEK organisms. * **Endocarditis with Colon Cancer:** Associated with *Streptococcus bovis* (now *S. gallolyticus*) [1].
Question 275: Typhoid intestinal perforation usually occurs in which week of typhoid fever?
- A. 2nd - 3rd week (Correct Answer)
- B. 4th - 5th week
- C. 5th - 7th week
- D. 6th - 8th week
Explanation: Explanation: Typhoid fever, caused by *Salmonella typhi*, is characterized by a predictable clinical progression involving the gut-associated lymphoid tissue (Peyer's patches). **Why Option A is correct:** Intestinal perforation is a classic late complication of typhoid fever, typically occurring during the **late 2nd or early 3rd week** of illness [1]. This timing corresponds to the pathological stage of **necrosis and ulceration** of the Peyer’s patches in the terminal ileum. After the initial inflammatory hyperplasia (1st week), the lymphoid tissue undergoes necrosis. If the ulceration extends deep through the muscularis and serosa, perforation occurs [1]. This is often heralded by a sudden drop in temperature and blood pressure, followed by signs of peritonitis. **Why other options are incorrect:** * **Options B, C, and D:** These timeframes (4th to 8th week) represent the period of convalescence or potential relapse. By the 4th week, in survivors, the ulcers typically begin to heal (granulation) without forming scars. While complications can rarely occur late in untreated cases, the peak incidence for perforation and hemorrhage is strictly the 2nd–3rd week [1]. **NEET-PG High-Yield Pearls:** * **Site of Perforation:** Most commonly occurs in the **terminal ileum** (within 60 cm of the ileocaecal valve) because Peyer’s patches are most numerous there. * **Pathological Stages:** 1st week (Hyperplasia/Peyer's patch swelling), 2nd week (Necrosis/Sloughing), 3rd week (Ulceration/Perforation), 4th week (Healing). * **Clinical Sign:** "Step-ladder" pattern fever is classic in the 1st week; "Rose spots" appear in the 2nd week. * **Diagnosis:** **Widal test** becomes positive in the 2nd week, while **Blood culture** is most sensitive in the 1st week (Mnemonic: **BASU** - Blood, Agglutination/Widal, Stool, Urine).
Question 276: Which of the following statements regarding Candida is true?
- A. Candida is a commensal on the skin. (Correct Answer)
- B. Oral candidiasis is common during pregnancy.
- C. Candida infections are common in the early stage of AIDS.
- D. Gram staining is the preferred method for diagnosing Candida infections.
Explanation: **Explanation:** **1. Why Option A is Correct:** *Candida albicans* and other species are part of the normal human flora. While they are primarily known as commensals of the **gastrointestinal tract** and **genitourinary tract**, they are also found as commensals on the **skin**, particularly in moist areas (intertriginous sites). Under conditions of immunosuppression or disrupted mucosal integrity, these commensals transition into opportunistic pathogens. **2. Why the Other Options are Incorrect:** * **Option B:** Oral candidiasis (thrush) is more common in infants, denture wearers, and the immunocompromised. **Vaginal candidiasis**, however, is the form specifically associated with pregnancy due to high estrogen levels and increased glycogen content in the vaginal mucosa. * **Option C:** Candida infections (specifically esophageal candidiasis) are considered **AIDS-defining illnesses**, typically occurring when the CD4 count falls below **200 cells/mm³**. This usually represents a late/advanced stage of HIV infection, not the early stage. * **Option D:** While *Candida* appears as Gram-positive budding yeast cells on a Gram stain, the **KOH (Potassium Hydroxide) mount** or **culture (Sabouraud Dextrose Agar)** are the preferred diagnostic methods. KOH dissolves host cellular debris, making the pseudohyphae and yeast cells more visible. **3. High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *C. albicans* is unique because it produces **Germ Tubes** (Reynolds-Braude phenomenon) when incubated in serum at 37°C for 2-3 hours. * **Culture:** On SDA, it forms creamy white, smooth colonies with a characteristic "yeasty" odor. * **Chlamydospores:** Produced on Cornmeal Agar (CMA). * **Drug of Choice:** Fluconazole is used for most localized infections; Echinocandins (e.g., Caspofungin) are preferred for systemic candidemia [1].
Question 277: What is the most common ocular infection following renal transplantation?
- A. Cytomegalovirus (Correct Answer)
- B. Toxoplasma
- C. Herpes virus
- D. EB virus
Explanation: **Explanation:** **Cytomegalovirus (CMV)** is the most common opportunistic viral infection and the leading cause of ocular morbidity in solid organ transplant (SOT) recipients, particularly following renal transplantation [1]. The risk is highest during the first 6 months post-transplant, coinciding with peak immunosuppression [1]. CMV retinitis typically presents as a "pizza-pie" or "cottage cheese and ketchup" fundus, characterized by necrotizing retinitis with associated hemorrhages. **Analysis of Options:** * **A. Cytomegalovirus (Correct):** CMV is the most frequent opportunistic pathogen in renal transplant patients due to the reactivation of latent virus or primary infection from the donor organ [1]. It is the primary cause of viral retinitis in this population. * **B. Toxoplasma:** While *Toxoplasma gondii* can cause chorioretinitis in immunocompromised hosts, it is significantly less common than CMV in the context of renal transplantation. * **C. Herpes Virus:** HSV and VZV can cause Acute Retinal Necrosis (ARN), but their incidence is lower than CMV in transplant recipients. * **D. EB Virus:** Epstein-Barr Virus is primarily associated with Post-Transplant Lymphoproliferative Disorder (PTLD) rather than direct ocular infections [2]. **High-Yield Clinical Pearls for NEET-PG:** * **Prophylaxis:** Valganciclovir is the drug of choice for CMV prophylaxis in high-risk renal transplant patients [1], [2]. * **Diagnosis:** CMV retinitis is a clinical diagnosis, but PCR of aqueous or vitreous humor can confirm it [1]. * **Treatment:** Intravenous Ganciclovir or oral Valganciclovir; foscarnet is used for resistant cases. * **Timeline:** Most CMV infections occur between 1 to 6 months post-transplant (the "middle period" of post-transplant infections) [1].
Question 278: A 24-year-old female presented to the ER with a characteristic rash and fever. On examination, a chronic lower extremity ulcer related to prior trauma, hypotension, and tachycardia were noted. Diffuse erythema was prominent on palms, conjunctiva, and oral mucosa. Lab findings revealed deranged RFTs, moderately increased SGOT and SGPT, and mild thrombocytopenia. The patient was resuscitated with IV fluid and vasopressors. Blood cultures were negative after 72 hours, and the patient's fingers started to desquamate. Which of the organisms is the most likely cause of the above condition?
- A. Staphylococcus aureus (Correct Answer)
- B. Hemophilus influenzae
- C. Enterococcus faecalis
- D. Streptococcus pneumoniae
Explanation: ### Explanation The clinical presentation is a classic case of **Staphylococcal Toxic Shock Syndrome (TSS)**. **1. Why Staphylococcus aureus is correct:** The patient meets the CDC diagnostic criteria for TSS: * **Fever and Hypotension:** Signs of systemic inflammatory response and shock. * **Diffuse Erythroderma:** A "sunburn-like" rash involving mucosal surfaces (conjunctiva, oral mucosa). * **Multisystem Involvement:** Deranged RFTs (Renal), elevated SGOT/SGPT (Hepatic), and thrombocytopenia (Hematologic). * **Desquamation:** Characteristically occurs 1–2 weeks after the onset of illness, particularly on palms and soles [1]. * **Negative Blood Cultures:** In Staphylococcal TSS, the symptoms are mediated by the **TSST-1 toxin** (a superantigen) acting from a localized site (the lower extremity ulcer). The bacteria themselves are rarely found in the blood (positive in <5% of cases), unlike Streptococcal TSS [1]. **2. Why the other options are incorrect:** * **Hemophilus influenzae:** Typically causes pneumonia, meningitis, or epiglottitis; it does not present with diffuse erythroderma or toxin-mediated desquamation. * **Enterococcus faecalis:** Usually associated with UTIs or endocarditis; it lacks the superantigen toxins required to produce this clinical triad. * **Streptococcus pneumoniae:** A common cause of sepsis and pneumonia, but it does not cause a desquamating rash. While *Streptococcus pyogenes* (Group A Strep) can cause TSS, it is usually associated with positive blood cultures and necrotizing fasciitis [1]. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** TSST-1 cross-links the MHC II molecule on APCs with the T-cell receptor (Vβ region), causing a massive "cytokine storm" (IL-1, IL-6, TNF-α, IFN-γ) [1]. * **Classic Scenarios:** Post-surgical wound infections, skin ulcers, or the use of highly absorbent tampons. * **Distinguishing Feature:** Staph TSS has **negative** blood cultures; Strep TSS often has **positive** blood cultures and more severe soft tissue pain [1]. * **Treatment:** Aggressive fluid resuscitation, source debridement, and clindamycin (to suppress toxin production).
Question 279: What is the drug of choice in a patient with severe complicated falciparum malaria?
- A. Chloroquine
- B. Quinine
- C. Artesunate (Correct Answer)
- D. Artemether
Explanation: The management of severe malaria has shifted significantly based on the **SEAQUAMAT** and **AQUAMAT** trials, which established **Intravenous (IV) Artesunate** as the gold standard. **1. Why Artesunate is the Correct Choice:** Artesunate is a water-soluble artemisinin derivative that provides rapid parasite clearance [1]. It acts on all erythrocytic stages of the parasite (including young rings), preventing further cytoadherence and sequestration in microvasculature—the hallmark of severe falciparum malaria [1]. Compared to Quinine, it has a superior safety profile, lower risk of hypoglycemia, and significantly reduces mortality rates [1]. **2. Why Other Options are Incorrect:** * **Chloroquine:** It is the drug of choice for sensitive *P. vivax* and uncomplicated malaria in specific regions, but high levels of resistance in *P. falciparum* make it ineffective for severe cases [1]. * **Quinine:** Formerly the drug of choice, it is now a second-line alternative. It requires slow infusion, cardiac monitoring (due to QT prolongation), and frequently causes "Cinchonism" and refractory hypoglycemia [1]. * **Artemether:** While an effective artemisinin, it is oil-based and absorbed erratically when given intramuscularly. IV Artesunate is preferred for its predictable pharmacokinetics in critically ill patients. **High-Yield Clinical Pearls for NEET-PG:** * **Dosage:** IV Artesunate is given at **2.4 mg/kg** at 0, 12, and 24 hours, then once daily. * **Switching:** Once the patient can tolerate orals, complete a full 3-day course of **ACT (Artemisinin-based Combination Therapy)** [1]. * **Side Effect:** Watch for **Delayed Post-Artesunate Hemolysis (PAH)**, which can occur 1–3 weeks after treatment. * **Pregnancy:** IV Artesunate is the drug of choice for severe malaria in **all trimesters** of pregnancy.
Question 280: Which of the following tests specifically detects Plasmodium falciparum?
- A. Lactate Dehydrogenase (LDH) assay
- B. Histidine-Rich Protein 2 (HRP-2) assay (Correct Answer)
- C. Thick blood film microscopy
- D. Quantitative Buffy Coat (QBC) analysis
Explanation: ### Explanation **Correct Answer: B. Histidine-Rich Protein 2 (HRP-2) assay** **1. Why HRP-2 is the correct answer:** The Histidine-Rich Protein 2 (HRP-2) is a water-soluble antigen produced specifically by the asexual stages and young gametocytes of **_Plasmodium falciparum_** [1]. Rapid Diagnostic Tests (RDTs) targeting HRP-2 are highly sensitive and specific for _P. falciparum_ only [1]. Because this protein is secreted into the bloodstream, it can be detected even when parasites are sequestered in the deep capillaries (a common phenomenon in falciparum malaria). **2. Why the other options are incorrect:** * **A. Lactate Dehydrogenase (LDH) assay:** This enzyme is produced by all four major human malaria species (_P. falciparum, P. vivax, P. ovale, P. malariae_). While some RDTs use specific isoforms to differentiate species, the LDH assay itself is generally considered a **pan-malarial marker** [1]. * **C. Thick blood film microscopy:** This is the "Gold Standard" for screening and quantifying parasite density. However, it is not specific to one species; it detects the presence of any _Plasmodium_ species. Differentiation requires a **thin film**. * **D. Quantitative Buffy Coat (QBC):** This is a fluorescent staining technique that enhances the detection of parasites in centrifuged blood [1]. Like microscopy, it is a general screening tool for malaria and does not specifically target _P. falciparum_ antigens. **Clinical Pearls for NEET-PG:** * **Persistent Positivity:** HRP-2 can remain positive in the blood for **2–4 weeks** even after successful treatment and parasite clearance [1]. Therefore, it cannot be used to monitor treatment response or detect immediate reinfection. * **Prozone Effect:** Very high parasitemia can sometimes lead to a false-negative HRP-2 result. * **Pan-malarial markers:** LDH and **Aldolase** are the markers used in RDTs to detect non-falciparum species or mixed infections.
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Viral Infections (Hepatitis, Herpes, etc.)
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Infection in Immunocompromised Hosts
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