Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 11: What is the period of isolation for Salmonella infection?

A. 72 hours after chemotherapy
B. Widal test negative
C. 3 consecutive stool cultures are negative (Correct Answer)
D. Urine culture is negative twice

Explanation: **Explanation:** The primary goal of isolation and discharge criteria in **Salmonella (Enteric Fever)** is to prevent the development of a carrier state and community transmission. **Why Option C is Correct:** According to standard public health guidelines (including WHO and Park’s Preventive and Social Medicine), a patient is considered non-infectious only when **three consecutive stool cultures**, taken at intervals of at least 24 hours, are **negative** for *Salmonella typhi*. This is the gold standard for ending isolation because fecal shedding can persist long after clinical symptoms subside. If the patient is a food handler, this protocol is strictly enforced to prevent outbreaks. **Analysis of Incorrect Options:** * **Option A:** 72 hours of chemotherapy may achieve clinical improvement, but it does not guarantee the elimination of the bacteria from the gallbladder or gut. * **Option B:** The **Widal test** measures antibodies (H and O antigens), not the presence of the live pathogen. Titers can remain high for months post-recovery, making it useless for determining the end of isolation. * **Option D:** While urine cultures are used in diagnosis (especially in the 2nd/3rd week), stool culture is the definitive medium for monitoring shedding and carrier status. **High-Yield Clinical Pearls for NEET-PG:** * **Carrier State:** Defined as persistence of *S. typhi* in stool/urine for **>1 year**. The most common site of colonization is the **gallbladder**. * **Drug of Choice:** Ceftriaxone (Injectable) or Azithromycin (Oral). * **Most sensitive test (1st week):** Bone marrow culture (though Blood culture is more common). * **Chronic Carrier Treatment:** High-dose Ampicillin or Cholecystectomy if gallstones are present.

Question 12: Which of the following is NOT part of the management of a grade III dog bite infected with rabies?

A. Vaccination
B. Suture the wound with antibiotic coverage (Correct Answer)
C. Wash with soap and water
D. Administration of antirabies serum and vaccination

Explanation: ### Explanation In the management of animal bites (especially Grade III), the primary goal is to prevent the rabies virus from entering the nerve endings. The correct answer is **B** because **suturing a potentially rabid wound is generally contraindicated.** #### 1. Why Option B is the Correct Answer (The "NOT" part) Suturing should be avoided because it can further inoculate the virus deeper into the tissues and cause mechanical trauma that facilitates viral entry into nerve endings. If suturing is functionally necessary (e.g., for massive lacerations or to stop life-threatening bleeding), it must be delayed by **24–48 hours** and performed only after infiltrating the wound with **Rabies Immunoglobulin (RIG)**. #### 2. Analysis of Incorrect Options * **Option C (Wash with soap and water):** This is the **most important first step**. Immediate flushing of the wound for 15 minutes with soap and running water mechanically removes the virus and disrupts its lipid envelope. * **Option D (Antirabies serum and vaccination):** Grade III bites (transdermal bites/scratches or licks on broken skin) require **Post-Exposure Prophylaxis (PEP)** consisting of both the Rabies Vaccine and Rabies Immunoglobulin (RIG/Serum). RIG provides immediate passive immunity until the vaccine-induced antibodies develop. * **Option A (Vaccination):** Modern cell-culture vaccines (IDRV or IM) are a mandatory component of PEP for all Grade II and III exposures. #### 3. NEET-PG High-Yield Pearls * **Grade I:** Touching/feeding animals (No PEP required). * **Grade II:** Nibbling of uncovered skin, minor scratches without bleeding (Vaccine only). * **Grade III:** Single/multiple transdermal bites, licks on broken skin, or contact with bats (Vaccine + RIG). * **Site of RIG:** The entire calculated dose of RIG should be infiltrated **into and around the wound**; any remainder is given IM at a site distant from the vaccine. * **Wound Care:** Avoid irritants like chilies, salt, or turmeric. Use virucidal agents like povidone-iodine if available.

Question 13: All of the following are true regarding diphtheria except?

A. Tonsillar membrane can be easily wiped off (Correct Answer)
B. There may be swelling of the neck causing a bull neck appearance
C. With a high degree of immunity, a membrane may never appear
D. In laryngeal diphtheria, tracheostomy may be needed to relieve respiratory obstruction

Explanation: ### Explanation **1. Why Option A is the correct answer (The "Except" statement):** In Diphtheria, the characteristic **pseudomembrane** is composed of fibrin, leukocytes, dead epithelial cells, and *Corynebacterium diphtheriae* bacilli. This membrane is **firmly adherent** to the underlying tissue. If an attempt is made to wipe it off or scrape it, it causes bleeding (a classic clinical sign). Therefore, the statement that it can be "easily wiped off" is false. **2. Analysis of Incorrect Options:** * **Option B:** In severe cases, extensive inflammation of the cervical lymph nodes and surrounding soft tissue leads to massive edema, giving the patient a characteristic **"Bull Neck" appearance**. * **Option C:** The formation of the membrane depends on the local action of the diphtheria toxin. If an individual has a **high degree of antitoxic immunity**, the toxin is neutralized before it can cause tissue necrosis, meaning a membrane may not develop despite infection. * **Option D:** Laryngeal involvement can lead to mechanical airway obstruction due to the membrane or edema. In such emergencies, a **tracheostomy** is a life-saving procedure to bypass the obstruction. ### High-Yield Clinical Pearls for NEET-PG: * **Agent:** *Corynebacterium diphtheriae* (Gram-positive, club-shaped, Chinese-letter pattern). * **Schick Test:** Used to demonstrate the immune status of an individual (susceptibility). * **Culture:** Löffler's serum slope (rapid growth) and Potassium Tellurite medium (black colonies). * **Treatment:** Prompt administration of **Diphtheria Antitoxin (ADS)** is the priority to neutralize circulating toxins; antibiotics (Erythromycin or Penicillin) are used to stop toxin production and clear the carrier state. * **Contact Management:** All contacts should receive a prophylactic dose of Erythromycin and a booster dose of the vaccine.

Question 14: What is the primary method for the control of Tuberculosis (TB) and leprosy?

A. Isolation of cases
B. Specific protection measures
C. Early diagnosis and treatment (Correct Answer)
D. Elimination of reservoirs

Explanation: The primary strategy for controlling Tuberculosis (TB) and Leprosy is **Early Diagnosis and Treatment**. This approach is based on the principle of **"Secondary Prevention,"** which aims to halt disease progression in the individual and, more importantly, break the chain of transmission in the community. ### Why "Early Diagnosis and Treatment" is Correct: Both TB and Leprosy are chronic bacterial infections where humans are the only significant reservoir. By initiating prompt treatment (DOTS for TB and MDT for Leprosy), the patient rapidly becomes non-infectious. For example, a TB patient typically becomes non-infectious within 2 weeks of starting effective chemotherapy, effectively neutralizing the source of infection. ### Why Other Options are Incorrect: * **Isolation of cases:** While historically used (sanatoriums), it is no longer practical or necessary. Modern chemotherapy renders patients non-infectious quickly, making home-based treatment the standard. * **Specific protection:** While the BCG vaccine exists for TB, its primary role is preventing severe childhood forms (miliary/meningeal TB) rather than stopping adult transmission. There is no widely used vaccine for Leprosy. * **Elimination of reservoirs:** Since humans are the reservoirs, "elimination" would imply curing every single infected person (including latent cases), which is a long-term goal of eradication rather than a primary control method. ### NEET-PG High-Yield Pearls: * **TB Control:** The National Strategic Plan (2017-2025) aims for TB elimination in India by 2025. The mainstay is the **"Test and Treat"** policy. * **Leprosy Control:** Under NLEP, the focus is on early detection through **Active Case Finding** (e.g., Leprosy Case Detection Campaigns) to prevent Grade 2 Disabilities (G2D). * **Epidemiological Concept:** For both diseases, the **Case Fatality Rate** is low, but the **Morbidity** is high; thus, early intervention is the most cost-effective public health measure.

Question 15: Under the Revised National Tuberculosis Control Program, which drug is used for chemoprophylaxis in children?

A. Rifampicin
B. Isoniazid (Correct Answer)
C. Ethambutol
D. Ciprofloxacin

Explanation: **Explanation** Under the National Tuberculosis Elimination Program (NTEP, formerly RNTCP), **Isoniazid (INH)** is the drug of choice for chemoprophylaxis. This strategy aims to prevent the progression of latent tuberculosis infection (LTBI) to active disease, particularly in vulnerable populations. **1. Why Isoniazid is Correct:** Isoniazid is highly bactericidal, cost-effective, and has a proven safety profile for long-term use in children. In India, chemoprophylaxis is indicated for **children <6 years of age** who are household contacts of a smear-positive pulmonary TB patient, regardless of their BCG vaccination status, provided active TB is ruled out. The standard dose is **5 mg/kg body weight daily for 6 months**. **2. Why Other Options are Incorrect:** * **Rifampicin:** While used in some global latent TB regimens (often as a 4-month course), it is not the primary drug for routine pediatric prophylaxis under NTEP guidelines. It is usually reserved for contacts of Isoniazid-resistant cases. * **Ethambutol:** This is a bacteriostatic drug and is not used alone for prophylaxis. Furthermore, it is generally avoided in very young children due to the difficulty in monitoring for optic neuritis (red-green color blindness). * **Ciprofloxacin:** This is a fluoroquinolone used in Multi-Drug Resistant (MDR-TB) regimens. It is never used for routine chemoprophylaxis to prevent the development of drug resistance. **High-Yield Clinical Pearls for NEET-PG:** * **Target Group:** Children <6 years and HIV-positive individuals (regardless of age) are the primary candidates for INH Prophylaxis. * **Dosage:** 5 mg/kg for 6 months. * **Pyridoxine (Vitamin B6):** Should be co-administered with INH in malnourished children and pregnant women to prevent peripheral neuropathy. * **Newer Guidelines:** NTEP is transitioning towards "TB Preventive Treatment" (TPT), which may include shorter regimens like 3HP (weekly Isoniazid + Rifapentine for 3 months).

Question 16: Under the National Malaria Eradication Programme (NMEP), what is the minimum annual blood examination rate that should be achieved?

A. 10% (Correct Answer)
B. 12%
C. 14%
D. 18%

Explanation: ### Explanation **1. Why the Correct Answer is Right (Option A: 10%)** The **Annual Blood Examination Rate (ABER)** is a critical operational indicator used to monitor the efficiency of malaria surveillance. It is defined as the number of blood slides examined for malaria parasites per 100 population per year. Under the National Malaria Eradication Programme (now integrated into the National Center for Vector Borne Diseases Control - NCVBDC), a **minimum ABER of 10%** is required. This threshold ensures that the surveillance system is sensitive enough to detect the majority of malaria cases in a community, reflecting adequate active and passive case detection. **2. Why the Other Options are Incorrect** * **Options B, C, and D (12%, 14%, 18%):** While higher ABER values indicate even more robust surveillance (and are often achieved in high-transmission areas), they are not the "minimum" standard set by the national program. ABER values below 10% are considered indicative of poor surveillance and under-reporting. **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **ABER Formula:** (Total number of slides examined / Total population) × 100. * **API (Annual Parasite Incidence):** The most sensitive index to measure malaria incidence in a locality. Formula: (Confirmed cases during the year / Population under surveillance) × 1000. * **SPR (Slide Positivity Rate):** (Total slides positive for malaria / Total slides examined) × 100. * **SFR (Slide Falciparum Rate):** (Total slides positive for *P. falciparum* / Total slides examined) × 100. * **Surveillance Types:** Active surveillance is done by health workers (fortnightly visits), while passive surveillance occurs at fixed health facilities. * **Elimination Goal:** India aims to be malaria-free by **2030**, with a transition from "control" to "elimination" strategies.

Question 17: A patient on antitubercular treatment shows sputum positivity at the end of the intensive phase under category I. What is the next step?

A. Continue treatment of intensive phase for one more month (Correct Answer)
B. Switch to category II treatment
C. Restart category I treatment
D. Start continuation phase under category I

Explanation: **Explanation:** The management of a patient who remains sputum-positive at the end of the Intensive Phase (IP) is a classic high-yield topic in Tuberculosis management. **Why Option A is correct:** Under the traditional RNTCP (Revised National Tuberculosis Control Programme) guidelines, if a patient remains smear-positive at the end of the 2-month Intensive Phase (IP) in Category I, the **IP is extended for one additional month**. The rationale is to ensure sputum conversion (from positive to negative) before moving to the Continuation Phase (CP), thereby reducing the bacterial load and preventing the emergence of drug resistance. **Why other options are incorrect:** * **Option B:** Switching to Category II (Retreatment regimen) is only indicated for "Treatment Failures," "Relapses," or "Treatment after Default." A single positive smear at the end of IP does not constitute failure. * **Option C:** Restarting the entire Category I treatment is unnecessary and increases the risk of toxicity without proven benefit at this stage. * **Option D:** Starting the Continuation Phase while the patient is still smear-positive increases the risk of treatment failure and the development of Multi-Drug Resistant TB (MDR-TB), as the CP uses fewer drugs (HR) compared to the IP (HRZE). **Clinical Pearls for NEET-PG:** * **Current NTEP Update:** Note that under the latest **Integrated National Tuberculosis Elimination Program (NTEP)** guidelines, the "extension of IP" has been largely phased out in favor of **Universal Drug Susceptibility Testing (UDST)**. If a patient is smear-positive at the end of IP now, the priority is to perform a **CBNAAT/GeneXpert** to rule out Rifampicin resistance. * **Sputum Conversion:** This is the most important prognostic indicator of treatment success. * **Category I Regimen:** 2 months of HRZE (IP) followed by 4 months of HRE (CP) in the daily regimen.

Question 18: What is the mortality rate of rabies?

A. 25%
B. 50%
C. 75%
D. 100% (Correct Answer)

Explanation: **Explanation:** **1. Why the Correct Answer is Right:** Rabies is a viral zoonosis caused by the Lyssavirus (Rhabdoviridae family). It is unique in clinical medicine because once the clinical symptoms appear, the disease is **virtually 100% fatal**. The virus is neurotropic, traveling via retrograde axonal transport to the central nervous system, leading to progressive encephalomyelitis. While there are a handful of documented cases of survival globally (often involving the controversial "Milwaukee Protocol"), for the purposes of public health and competitive exams like NEET-PG, the case fatality rate is considered absolute (100%). **2. Why the Incorrect Options are Wrong:** * **Options A, B, and C (25%, 50%, 75%):** These figures significantly underestimate the lethality of the virus. While many infectious diseases (like Tetanus or Ebola) have high mortality rates ranging from 10% to 90%, Rabies stands alone as the only infectious disease where death is the inevitable outcome following the onset of symptoms. **3. High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** Highly variable (usually 1–3 months), but can range from <7 days to >1 year. It depends on the site of the bite (closer to the CNS = shorter incubation). * **Diagnosis:** The presence of **Negri bodies** (intracytoplasmic inclusion bodies) in the hippocampus or cerebellum is pathognomonic (post-mortem). * **Prevention:** Since there is no cure, post-exposure prophylaxis (PEP) is the only way to prevent death. This includes wound toilet, Rabies vaccine, and Rabies Immunoglobulin (RIG) for Category III bites. * **Hydrophobia:** This classic sign is due to spasms of the pharyngeal muscles when attempting to swallow liquids.

Question 19: A resident doctor sustained a needle stick injury while sampling blood from an HIV-positive patient. A decision is made to offer the doctor post-exposure prophylaxis. Which one of the following would be the best recommendation?

A. Zidovudine + Lamivudine for 4 weeks
B. Zidovudine + Lamivudine + Nevirapine for 4 weeks
C. Zidovudine + Lamivudine + Indinavir for 4 weeks (Correct Answer)
D. Zidovudine + Stavudine + Nevirapine for 4 weeks

Explanation: **Explanation:** The management of needle stick injuries (NSI) in healthcare workers depends on the risk assessment of the exposure. In this scenario, the source is a known HIV-positive patient, necessitating **Post-Exposure Prophylaxis (PEP)**. **1. Why Option C is Correct:** According to the classic NACO and WHO guidelines (often tested in NEET-PG), PEP is categorized into Basic and Expanded regimens. For **high-risk exposures** (large bore needle, deep injury, or source with high viral load/advanced AIDS), an **Expanded Regimen** is indicated. This consists of **two NRTIs (Zidovudine + Lamivudine)** plus a **Protease Inhibitor (Indinavir or Lopinavir/Ritonavir)**. The standard duration for PEP is **4 weeks (28 days)**. **2. Why the Other Options are Incorrect:** * **Option A:** This is a "Basic Regimen." While used for low-risk exposures, the presence of a known HIV-positive source often warrants the addition of a third drug for maximum efficacy. * **Option B & D:** These include **Nevirapine**. Nevirapine is strictly **contraindicated** in PEP because it carries a high risk of severe hepatotoxicity and Stevens-Johnson Syndrome in HIV-negative individuals receiving it for prophylaxis. * **Option D:** Combining Zidovudine and Stavudine is avoided due to pharmacological antagonism (both compete for the same phosphorylation pathway). **3. High-Yield Clinical Pearls for NEET-PG:** * **Ideal Timing:** PEP should be started as soon as possible, ideally within **2 hours**, and definitely within **72 hours** of exposure. * **Current NACO Update:** While older questions focus on Indinavir, the current preferred NACO regimen is **Tenofovir (300mg) + Lamivudine (300mg) + Dolutegravir (50mg)** as a single daily pill for 28 days. * **Testing Schedule:** Follow-up HIV testing for the exposed professional should be done at baseline, 6 weeks, 12 weeks, and occasionally at 6 months.

Question 20: DOTS chemotherapy is given for which condition?

A. Tuberculosis (TB) (Correct Answer)
B. Leprosy
C. Acquired Immunodeficiency Syndrome (AIDS)
D. Tetanus

Explanation: **Explanation:** **DOTS (Directly Observed Treatment, Short-course)** is the internationally recommended strategy for the control of **Tuberculosis (TB)**. It was launched by the WHO and adopted in India under the Revised National Tuberculosis Control Programme (RNTCP), now known as the National TB Elimination Programme (NTEP). The core medical concept behind DOTS is to ensure **treatment adherence** and prevent the emergence of Multi-Drug Resistant TB (MDR-TB). It involves a trained health worker or designated individual watching the patient swallow their medication, ensuring the right drugs are taken in the right doses at the right intervals. **Analysis of Incorrect Options:** * **Leprosy:** Managed via **MDT (Multi-Drug Therapy)** involving Rifampicin, Dapsone, and Clofazimine. While treatment is supervised, it is not termed "DOTS." * **AIDS:** Managed using **ART (Antiretroviral Therapy)**. While adherence is critical, the specific DOTS framework is not the standard delivery model. * **Tetanus:** This is a non-communicable infectious disease caused by *Clostridium tetani* toxins. It is managed with wound debridement, Tetanus Immunoglobulin (TIG), and vaccination, not long-term chemotherapy. **High-Yield Clinical Pearls for NEET-PG:** * **Five Components of DOTS:** Political commitment, Good diagnosis (Sputum Microscopy/NAAT), Uninterrupted supply of quality drugs, Systematic recording/reporting, and Direct observation of treatment. * **NTEP Update:** India aims to eliminate TB by **2025** (5 years ahead of the global SDG target). * **Nikshay Portal:** The unified ICT platform for TB surveillance and patient management in India. * **Daily Regimen:** Under NTEP, TB treatment has shifted from intermittent (thrice weekly) to a **fixed-dose combination (FDC) daily regimen** based on the patient's weight.

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