Infectious Diseases Practice Questions

Q: Which of the following is the drug of first choice for Non-Gonococcal Urethritis?

Doxycycline. **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.

Q: Typhoid intestinal perforation usually occurs in which week of typhoid fever?

2nd - 3rd week. 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).

Q: Which of the following statements regarding Candida is true?

Candida is a commensal on the skin.. **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].

Q: What is the most common ocular infection following renal transplantation?

Cytomegalovirus. **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].

Q: What is the drug of choice in a patient with severe complicated falciparum malaria?

Artesunate. 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.

Q: Which of the following tests specifically detects Plasmodium falciparum?

Histidine-Rich Protein 2 (HRP-2) assay. ### 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.

Question 1

Which of the following is the drug of first choice for Non-Gonococcal Urethritis?

Accepted Answer

Doxycycline

Answer

Ceftriaxone

Answer

Ciprofloxacin

Answer

Minocycline

Question 2

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?

Accepted Answer

Complete resolution

Answer

Cirrhosis

Answer

Establishment of a chronic carrier state

Answer

Fulminant hepatitis

Question 3

Which of the following statements is true about HIV?

Accepted Answer

Male-to-female transmission of HIV is higher than female-to-male transmission.

Answer

HIV is not transmitted through semen.

Answer

There are more chances of HIV transmission during LSCS than normal labor.

Answer

HIV is more infectious than hepatitis B.

Question 4

What is the most common cause of acute bacterial endocarditis?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus viridans

Answer

Streptococcus intermedius

Answer

Candida albicans

Question 5

Typhoid intestinal perforation usually occurs in which week of typhoid fever?

Accepted Answer

2nd - 3rd week

Answer

4th - 5th week

Answer

5th - 7th week

Answer

6th - 8th week

Question 6

Which of the following statements regarding Candida is true?

Accepted Answer

Candida is a commensal on the skin.

Answer

Oral candidiasis is common during pregnancy.

Answer

Candida infections are common in the early stage of AIDS.

Answer

Gram staining is the preferred method for diagnosing Candida infections.

Question 7

What is the most common ocular infection following renal transplantation?

Accepted Answer

Cytomegalovirus

Answer

Toxoplasma

Answer

Herpes virus

Answer

EB virus

Question 8

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?

Accepted Answer

Staphylococcus aureus

Answer

Hemophilus influenzae

Answer

Enterococcus faecalis

Answer

Streptococcus pneumoniae

Question 9

What is the drug of choice in a patient with severe complicated falciparum malaria?

Accepted Answer

Artesunate

Answer

Chloroquine

Answer

Quinine

Answer

Artemether

Question 10

Which of the following tests specifically detects Plasmodium falciparum?

Accepted Answer

Histidine-Rich Protein 2 (HRP-2) assay

Answer

Lactate Dehydrogenase (LDH) assay

Answer

Thick blood film microscopy

Answer

Quantitative Buffy Coat (QBC) analysis

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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