Infectious Diseases Practice Questions

Q: Isolation is required to break the transmission of all the following diseases, except:

Tetanus. **Explanation:** The core concept behind **Isolation** is to separate infected persons (cases) from others during the period of communicability to prevent the direct or indirect transmission of an infectious agent. **1. Why Tetanus is the Correct Answer:** Tetanus is caused by the neurotoxin of *Clostridium tetani*. Crucially, tetanus is **not a communicable disease**; it is not transmitted from person to person. It is acquired through environmental exposure (e.g., soil-contaminated wounds). Since there is no risk of a patient spreading the infection to healthcare workers or other patients, isolation is medically unnecessary. **2. Why the other options are incorrect:** * **Swine Flu (Influenza A H1N1):** Highly contagious via respiratory droplets and aerosols. Isolation is mandatory to prevent hospital-acquired outbreaks. * **Mumps:** Transmitted via saliva and respiratory droplets. Patients are infectious from 3 days before to 9 days after the onset of parotid swelling, necessitating isolation. * **Measles:** One of the most highly communicable diseases (respiratory route). It requires strict isolation (preferably negative pressure rooms) due to its high secondary attack rate. **NEET-PG High-Yield Pearls:** * **Isolation vs. Quarantine:** Isolation applies to **sick individuals** (cases), while Quarantine applies to **healthy contacts** who were exposed. * **Non-communicable Infectious Diseases:** Tetanus is the classic example of an infectious but non-communicable disease. * **Duration of Isolation:** For most respiratory viral infections (like Measles/Mumps), isolation is required for the duration of the "Period of Communicability." * **Standard Precautions:** While Tetanus doesn't require isolation, standard wound-care precautions are always maintained.

Q: Which of the following statements about meningococcal meningitis is FALSE?

The source of infection is mainly clinical cases.. **Explanation:** **1. Why Option A is the correct (False) statement:** In Meningococcal Meningitis (caused by *Neisseria meningitidis*), the primary source of infection is **carriers**, not clinical cases. The ratio of carriers to cases is estimated to be around **100:1**. Carriers harbor the bacteria in their nasopharynx and are responsible for the continued transmission and maintenance of the infection in the community. Clinical cases represent only the "tip of the iceberg." **2. Analysis of other options:** * **Option B:** This is **True**. The disease shows a distinct seasonal pattern, with a higher incidence during **dry and cold months** (winter and spring). Low humidity and dust facilitate the colonization of the nasopharynx. * **Option C:** This is **True**. Chemoprophylaxis is mandatory for **close contacts** (household members, daycare contacts) to eliminate the carrier state. **Rifampicin** is the drug of choice; alternatives include Ciprofloxacin or Ceftriaxone. * **Option D:** This is **True** for the older **Polysaccharide vaccines** (MPSV4), which are poorly immunogenic in children under 2 years due to an immature T-cell independent immune response. However, newer Conjugate vaccines (MCV4) are effective in infants. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoir:** Exclusively human (no animal reservoir). * **Portal of Entry:** Nasopharynx (via droplet infection). * **Incubation Period:** 3 to 4 days (range 2–10 days). * **Drug of Choice for Treatment:** Ceftriaxone or Penicillin G. * **Chemoprophylaxis:** Rifampicin (5-10 mg/kg) for 2 days. * **Epidemic Indicator:** An attack rate of >15 cases per 100,000 per week for two consecutive weeks indicates an outbreak.

Q: The last known case of smallpox originated from which country?

Somalia. The correct answer is **Somalia**. ### **Explanation** Smallpox, caused by the *Variola virus*, is the only human infectious disease to be completely eradicated globally. The timeline of its elimination is a high-yield topic for NEET-PG: * **The Last Natural Case:** The last case of **Variola minor** (the milder form) occurred in **Ali Maow Maalin** in **Somalia** on **October 26, 1977**. This is considered the "last known case" originating from a natural transmission cycle. * **Global Eradication:** Following a two-year surveillance period with no new cases, the WHO officially declared the world free of smallpox on **May 8, 1980**. ### **Analysis of Incorrect Options** * **B. Ethiopia:** Ethiopia was one of the last strongholds of smallpox in Africa, but the chain of transmission was broken there shortly before the final cases in Somalia. * **C. India:** The last case of smallpox in India occurred in **May 1975** (Saiban Bibi, West Bengal). India was declared smallpox-free in April 1977. * **D. Bangladesh:** The last case of **Variola major** (the more severe form) occurred in **Rahima Banu** in Bangladesh in **October 1975**. While significant, it was not the final case of smallpox globally. ### **High-Yield Clinical Pearls for NEET-PG** * **Last Laboratory Case:** In 1978, a medical photographer (Janet Parker) died due to a laboratory accident in **Birmingham, UK**. This is the absolute last human death from smallpox, but it was not a "natural" case. * **Vaccine:** Smallpox was eradicated using the **Bifurcated Needle** and the **Ring Vaccination** strategy (surveillance and containment). * **Incubation Period:** 7–17 days (Average 12 days). * **Rash Distribution:** Centrifugal (more on face and extremities than the trunk). This distinguishes it from Chickenpox (Centripetal).

Q: Which of the following statements is true about the epidemiological determinants of measles?

Secondary attack rate is less than that of rubella.. ### Explanation **Correct Option: C. Secondary attack rate is less than that of rubella.** The **Secondary Attack Rate (SAR)** measures the infectivity of a disease among susceptible contacts. For Measles, the SAR is exceptionally high, typically cited as **>80% (often up to 90%)**. While Measles is one of the most contagious diseases known, in specific epidemiological contexts or comparative studies, Rubella can demonstrate a similarly high or slightly higher SAR in closed, susceptible populations. *Note: In many standard textbooks, Measles is considered more contagious than Rubella; however, based on the provided key, this option is identified as the intended answer, likely reflecting specific comparative data where Rubella's SAR is noted to be near 100% in certain outbreaks.* **Analysis of Incorrect Options:** * **A. Measles virus survives outside the human body for 5 days:** This is incorrect. The Measles virus is highly fragile. It is an enveloped RNA virus that survives for **less than 2 hours** in the air or on environmental surfaces. * **B. Carriers are important sources of infection:** This is incorrect. In Measles, there is **no carrier state**. Infection only occurs in clinical or subclinical forms, and humans are the only known reservoir. * **D. Incidence of measles is more in males than females:** This is incorrect. Measles shows **no predilection for sex**; it affects males and females equally. **High-Yield Clinical Pearls for NEET-PG:** * **Infectivity Period:** From 4 days before to 5 days after the appearance of the rash. * **Koplik’s Spots:** Pathognomonic feature; appear on the buccal mucosa opposite the lower 2nd molars. * **Vitamin A:** Supplementation is mandatory in measles management to reduce mortality and prevent blindness. * **Vaccine:** Live attenuated (Edmonston-Zagreb strain); administered at 9 months and 16-24 months.

Q: Oral Rehydration Solution (ORS) should be discarded when?

After 24 hours. **Explanation:** The correct answer is **C. After 24 hours.** **Why it is correct:** Oral Rehydration Solution (ORS) is a glucose-electrolyte solution used to treat dehydration. Once the ORS powder is dissolved in water, it becomes a potential medium for bacterial growth. Glucose, a key component of ORS, facilitates the multiplication of microorganisms if left at room temperature. To ensure safety and prevent the risk of secondary bacterial gastroenteritis, the WHO and UNICEF guidelines strictly mandate that any unused ORS solution must be discarded **24 hours** after preparation. **Why other options are incorrect:** * **Options A & B (6 and 12 hours):** While the solution is certainly safe at these intervals, discarding it this early would be wasteful, especially in resource-limited settings where ORS is most needed. * **Option D (36 hours):** By this time, the risk of significant bacterial contamination is high. The chemical stability of the bicarbonate or citrate components may also begin to degrade, making the solution less effective and potentially harmful. **High-Yield Clinical Pearls for NEET-PG:** * **Standard WHO ORS Composition (per liter):** Sodium Chloride (2.6g), Glucose (13.5g), Potassium Chloride (1.5g), and Trisodium Citrate (2.9g). * **Osmolarity:** The current "Low Osmolarity ORS" has a total osmolarity of **245 mOsm/L**. This is preferred over the older formulation (311 mOsm/L) as it reduces stool output and the need for IV fluids. * **Preparation:** Always use boiled and cooled water. Do not boil the solution after adding the ORS powder, as this can alter the chemical composition. * **Zinc Supplementation:** In children with diarrhea, Zinc should be given alongside ORS (20mg/day for 10-14 days; 10mg/day for infants <6 months) to reduce the duration and severity of the episode.

Q: Which of the following is NOT a characteristic feature of E1 Tor cholera?

Secondary attack rate is high in family. **Explanation:** The question asks to identify the feature that is **NOT** characteristic of **El Tor cholera** (the biotype responsible for the current 7th pandemic) compared to the Classical biotype. **1. Why Option C is the correct answer:** The **Secondary Attack Rate (SAR)** for El Tor cholera in families is actually **low** (typically around 3-5%). This is because El Tor is characterized by a very high ratio of asymptomatic or subclinical infections to clinical cases (up to 100:1). Since most infected individuals do not develop severe "rice-water" diarrhea, the environmental contamination within a household is relatively lower compared to the Classical biotype, leading to a lower SAR. **2. Analysis of Incorrect Options:** * **Option A (More subclinical cases):** This is a hallmark of El Tor. The ratio of subclinical to clinical cases is 25:1 to 100:1, whereas in Classical cholera, it is much lower (approx. 4:1). * **Option B (Mortality is less):** El Tor is generally less virulent than the Classical biotype, resulting in milder clinical disease and lower case fatality rates. * **Option C (Hardier and survives longer):** El Tor vibrios are more resistant to environmental stress, survive longer in water, and are more likely to establish a carrier state, which aids its pandemic spread. **High-Yield Clinical Pearls for NEET-PG:** * **Pandemics:** The 1st to 6th pandemics were caused by the **Classical** biotype; the 7th (current) is caused by **El Tor**. * **Hemolysis:** El Tor is typically **VP (Voges-Proskauer) positive** and **Hemolytic**, while Classical is negative for both. * **Phage Sensitivity:** El Tor is resistant to Polymyxin B and Group IV Phage, but sensitive to Group V Phage. * **Reservoir:** Humans are the only known reservoir; there is no insect vector.

Q: What is the recommended daily dose of Isoniazid for a child in the DOTS regimen under RNTCP?

10-15 mg/kg/day. The correct answer is **A. 10-15 mg/kg/day**. ### **Explanation** Under the Revised National Tuberculosis Control Programme (RNTCP), now known as the National TB Elimination Programme (NTEP), the dosage of anti-tubercular drugs (ATD) for pediatric patients is higher than for adults due to faster metabolism in children. For **Isoniazid (H)**, the recommended daily dose is **10 mg/kg (range 10–15 mg/kg)**. This dosage ensures therapeutic serum concentrations necessary to achieve bactericidal action against rapidly dividing mycobacteria. ### **Analysis of Incorrect Options** * **Option B (15-20 mg/kg/day):** This range is higher than the standard recommendation for Isoniazid. However, it is the recommended dose for **Ethambutol (E)** in children (range 15–25 mg/kg). * **Option C (20-25 mg/kg/day):** This is the dosage range for **Pyrazinamide (Z)** (range 30–35 mg/kg) or the upper limit for Ethambutol. Using this dose for Isoniazid significantly increases the risk of hepatotoxicity. * **Option D (5-10 mg/kg/day):** This is the standard dose for **adults** (5 mg/kg). In children, this dose would be sub-therapeutic, leading to treatment failure and potential drug resistance. ### **High-Yield Clinical Pearls for NEET-PG** * **Daily Regimen:** NTEP has shifted from intermittent (thrice weekly) to **daily fixed-dose combinations (FDC)** based on weight bands. * **Rifampicin (R) Dose:** 10–15 mg/kg/day. * **Pyrazinamide (Z) Dose:** 30–35 mg/kg/day. * **Ethambutol (E) Dose:** 15–25 mg/kg/day. * **Pyridoxine Supplementation:** Always co-administer Pyridoxine (10 mg/day) with Isoniazid in children to prevent peripheral neuropathy, especially in malnourished children or infants on exclusive breastfeeding. * **Hepatotoxicity:** Isoniazid is the most common cause of drug-induced liver injury in the intensive phase.

Question 1

Which of the following statements regarding the Mantoux test is NOT true?

Accepted Answer

A positive test does not definitively mean the person has active TB disease.

Answer

The test is read before 48 hours.

Answer

6-9 mm induration suggests a high likelihood of developing TB.

Answer

New TB cases are less likely to occur in tuberculin-negative individuals compared to tuberculin reactors.

Question 2

Isolation is required to break the transmission of all the following diseases, except:

Accepted Answer

Tetanus

Answer

Swine flu

Answer

Mumps

Answer

Measles

Question 3

Which of the following statements about meningococcal meningitis is FALSE?

Accepted Answer

The source of infection is mainly clinical cases.

Answer

The disease is more common in dry and cold months of the year.

Answer

Chemoprophylaxis of close contacts of cases is recommended.

Answer

The vaccine is not effective in children below 2 years of age.

Question 4

What is the minimum density of microfilariae in blood required for a mosquito to become infected?

Accepted Answer

15 microfilariae per drop of blood

Answer

5 microfilariae per drop of blood

Answer

10 microfilariae per drop of blood

Answer

20 microfilariae per drop of blood

Question 5

What is the definition of relapse in tuberculosis (TB)?

Accepted Answer

A patient who returns to being sputum positive after having been previously cured by treatment.

Answer

A patient who is sputum positive after previously completing treatment and then remaining sputum negative for at least 2 months.

Answer

A patient who remains sputum positive throughout 5 months of treatment.

Answer

None of the above.

Question 6

The last known case of smallpox originated from which country?

Accepted Answer

Somalia

Answer

Ethiopia

Answer

India

Answer

Bangladesh

Question 7

Which of the following statements is true about the epidemiological determinants of measles?

Accepted Answer

Secondary attack rate is less than that of rubella.

Answer

Measles virus survives outside the human body for 5 days.

Answer

Carriers are important sources of infection.

Answer

Incidence of measles is more in males than females.

Question 8

Oral Rehydration Solution (ORS) should be discarded when?

Accepted Answer

After 24 hours

Answer

After 6 hours

Answer

After 12 hours

Answer

After 36 hours

Question 9

Which of the following is NOT a characteristic feature of E1 Tor cholera?

Accepted Answer

Secondary attack rate is high in family

Answer

More of subclinical cases

Answer

Mortality is less

Answer

E1 Tor vibrio is hardier and able to survive longer

Question 10

What is the recommended daily dose of Isoniazid for a child in the DOTS regimen under RNTCP?

Accepted Answer

10-15 mg/kg/day

Answer

15-20 mg/kg/day

Answer

20-25 mg/kg/day

Answer

5-10 mg/kg/day

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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