Infectious Diseases Practice Questions

Q: What is true about the epidemiology of influenza?

Extra-human reservoirs are seen.. ### Explanation **Correct Answer: D. Extra-human reservoirs are seen.** Influenza viruses, particularly **Influenza A**, exhibit a vast extra-human reservoir. They infect a wide range of animals and birds (e.g., ducks, chickens, pigs, horses, and seals). These reservoirs are crucial for the emergence of new subtypes through **antigenic shift** (genetic reassortment), which can lead to pandemics. In contrast, Influenza B and C are almost exclusively human pathogens. **Analysis of Incorrect Options:** * **A. Asymptomatic cases are seen rarely:** This is incorrect. Subclinical or asymptomatic infections are quite common in influenza and play a significant role in the rapid spread of the virus within a community. * **B. The incubation period is 10-12 hours:** This is incorrect. The incubation period for influenza is typically **1 to 4 days**, with an average of **2 days**. It is short, but not as brief as 10 hours. * **C. Pandemics are rare:** While pandemics do not occur every year, they are a characteristic feature of Influenza A. Major pandemics have occurred at intervals (e.g., 1918, 1957, 1968, and 2009). The statement is misleading because the *potential* for pandemics is a defining epidemiological trait of the virus. **High-Yield NEET-PG Pearls:** * **Antigenic Shift:** Major abrupt change (reassortment) in Influenza A only; leads to **Pandemics**. * **Antigenic Drift:** Minor point mutations in Influenza A and B; leads to **Epidemics** and necessitates annual vaccine updates. * **Period of Communicability:** Adults are infectious from 1 day before to 5 days after the onset of symptoms. * **Drug of Choice:** Oseltamivir (Neuraminidase inhibitor) is the preferred treatment for both seasonal and avian flu. * **Vaccine:** The most common is the **Inactivated (killed)** vaccine given IM; the Live Attenuated Influenza Vaccine (LAIV) is administered intranasally.

Q: Which index is used to measure the operational efficiency of malaria control programs?

Annual Blood Examination Rate (ABER). ### Explanation **1. Why ABER is the Correct Answer** The **Annual Blood Examination Rate (ABER)** is the primary indicator used to measure the **operational efficiency** and performance of the surveillance system in a malaria control program. It represents the percentage of the population screened for malaria parasites in a year. * **Formula:** (Number of blood slides examined / Total population) × 100. * **Significance:** For a program to be considered effective in a malaria-endemic area, a minimum ABER of **10%** is required. It ensures that the "case-finding" machinery is active and sensitive enough to detect the parasite reservoir in the community. **2. Analysis of Incorrect Options** * **Annual Parasite Incidence (API):** This measures the **incidence of malaria** (morbidity) in a community. It is the main criteria used to categorize areas for different intervention strategies under the National Framework for Malaria Elimination (NFME). * **Infant Parasite Rate:** This is the most sensitive index to measure **recent transmission** of malaria in a locality. If an infant (under 1 year) is positive, it proves that the infection was acquired recently. * **Spleen Rate:** Used primarily to measure **malaria endemicity** in a community. It is measured in children aged 2–9 years. **3. NEET-PG High-Yield Pearls** * **ABER = Operational Efficiency** (Process indicator). * **API = Disease Burden** (Impact indicator). * **Slide Positivity Rate (SPR):** Used to monitor the trend of malaria when ABER is constant. * **Slide Falciparum Rate (SFR):** Specifically monitors the prevalence of *P. falciparum*. * **Malaria Elimination Target:** API < 1 per 1000 population at risk.

Q: All of the following are true regarding diphtheria except?

Tonsillar membrane can be easily wiped off. ### 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.

Q: Which of the following statements about the composition of the new Oral Rehydration Solution (ORS) is incorrect?

Total osmolarity: 300 mmol/L. The question asks for the **incorrect** statement regarding the composition of the WHO-recommended **Low Osmolarity ORS**. ### **Explanation of the Correct Answer (D)** The total osmolarity of the new (reduced osmolarity) ORS is **245 mmol/L**, not 300 mmol/L. The WHO shifted from the standard ORS (311 mmol/L) to this new formula to reduce the risk of hypernatremia, decrease stool output, and minimize the need for unscheduled intravenous fluids. ### **Analysis of Incorrect Options (Correct Components)** * **A. Sodium chloride (2.6 g/L):** This is the correct weight for NaCl in the new formula. It provides 75 mmol/L of Sodium and 65 mmol/L of Chloride. * **B. Potassium chloride (1.5 g/L):** This is correct. It provides 20 mmol/L of Potassium and 20 mmol/L of Chloride, essential for replacing losses during diarrhea. * **C. Glucose (13.5 g/L):** This is correct. It provides 75 mmol/L of anhydrous glucose. Glucose is vital for the co-transport of sodium via the SGLT-1 receptors in the small intestine. ### **High-Yield Clinical Pearls for NEET-PG** * **Composition in mmol/L (The 75-75-20 Rule):** * Sodium: **75** * Glucose: **75** * Chloride: **65** * Potassium: **20** * Citrate: **10** * **Total Osmolarity: 245 mmol/L** * **Trisodium Citrate (2.9 g/L):** Added to correct metabolic acidosis and increase the shelf life of ORS compared to bicarbonate. * **Re-Somal:** A special ORS for **Severely Malnourished** children. It has lower Sodium (45 mmol/L) and higher Potassium (40 mmol/L) to prevent fluid overload and address chronic potassium depletion.

Q: Chemoprophylaxis is indicated for all of the following conditions except?

Measles. **Explanation:** The core concept behind **chemoprophylaxis** is the administration of specific drugs (usually antibiotics) to prevent the development of an infection in exposed individuals. **Why Measles is the Correct Answer:** Measles is a viral infection. Chemoprophylaxis is generally ineffective against viral diseases because antibiotics do not act on viruses. Prevention of measles relies on **immunoprophylaxis** (active immunization with the MMR/MR vaccine or passive immunization with Immunoglobulins in specific high-risk exposures). Therefore, there is no "chemoprophylaxis" for measles. **Analysis of Incorrect Options:** * **Cholera:** Chemoprophylaxis is indicated for household contacts. The drug of choice (DOC) is **Doxycycline** (single dose); alternatively, Tetracycline or Azithromycin is used. * **Meningococcal Meningitis:** This is a classic indication for chemoprophylaxis to eradicate the nasopharyngeal carrier state in close contacts. The DOC is **Rifampicin**; Ciprofloxacin or Ceftriaxone are alternatives. * **Conjunctivitis:** In cases of neonatal exposure (Ophthalmia neonatorum) or bacterial outbreaks (e.g., Trachoma), topical or systemic antibiotics (like Erythromycin or Tetracycline) are used as prophylaxis. **High-Yield Clinical Pearls for NEET-PG:** * **DOC for Chemoprophylaxis:** * **Rheumatic Fever:** Penicillin G (Long-acting Benzathine Penicillin). * **Plague:** Tetracycline or Doxycycline. * **Leptospirosis:** Doxycycline (200 mg once weekly). * **Pertussis:** Erythromycin. * **Diphtheria:** Erythromycin or Penicillin. * **Note:** Chemoprophylaxis is **not** recommended for mass use in Cholera; it is strictly for household contacts to prevent secondary spread.

Q: What is the most important source of infection for meningococci?

Carriers. **Explanation:** The correct answer is **Carriers**. In the epidemiology of Meningococcal meningitis (*Neisseria meningitidis*), the human nasopharynx is the only natural reservoir. **1. Why Carriers are the most important source:** For every clinical case, there are hundreds of carriers. Carriers are individuals who harbor the organism in their nasopharynx without showing symptoms. They are the primary reservoir and the main source of infection in the community because they are mobile, undetected, and outnumber clinical cases by a ratio of roughly **100:1** (up to 1000:1 during epidemics). The "carrier state" is essential for the continued survival and transmission of the bacteria. **2. Why other options are incorrect:** * **A Case of Meningitis:** While cases are infectious, they are usually isolated or hospitalized quickly, limiting their contact with the general population. They represent only the "tip of the iceberg." * **Subclinical Case:** While subclinical infections occur, the term "carrier" is the standard epidemiological descriptor for the asymptomatic spread of meningococci. * **Latent Case:** Latency refers to an infection that is hidden and not currently shedding the pathogen (like TB or Herpes). Meningococci are actively shed from the nasopharynx of carriers, making "carrier" the more accurate term. **High-Yield Pearls for NEET-PG:** * **Carrier Rate:** In endemic areas, the carrier rate is usually 5-10%. If the rate exceeds **20%**, it is a warning sign of an impending epidemic. * **Type of Carrier:** "Temporary" or "Transient" carriers are most common. * **Portal of Entry:** Nasopharynx. * **Chemoprophylaxis of choice:** **Rifampicin** (Drug of choice for contacts); Ciprofloxacin or Ceftriaxone are alternatives. * **Best Indicator of Transmission:** The prevalence of nasopharyngeal carriers.

Q: What is the recommended prophylaxis for cholera?

Doxycycline 300mg once daily. **Explanation:** The correct answer is **Doxycycline 300mg once daily**. **1. Why Doxycycline is Correct:** In the management of cholera, chemoprophylaxis is recommended only for **household contacts** (close contacts) of a confirmed case. **Doxycycline** is the drug of choice for adults because it effectively reduces the duration of diarrhea and the excretion of *Vibrio cholerae*. The standard prophylactic dose for an adult is a **single dose of 300 mg**. It works by inhibiting bacterial protein synthesis (30S subunit). **2. Why Other Options are Incorrect:** * **Cephalosporins (Option B):** While some third-generation cephalosporins have activity against Gram-negative bacteria, they are not the standard of care for cholera prophylaxis and are less effective than tetracyclines in reducing stool volume. * **Streptomycin (Option C):** This is an aminoglycoside primarily used for Tuberculosis and Plague. It is not used for cholera due to poor oral absorption and lack of efficacy against *V. cholerae*. * **Cotrimoxazole (Option D):** Previously used as an alternative, but widespread resistance has made it less reliable. It is currently reserved for children or pregnant women only if other first-line drugs are unavailable. **3. High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC) for Treatment:** Doxycycline (Single dose 300mg). * **DOC for Children/Pregnant Women:** Azithromycin (Single dose 500mg or 20mg/kg). * **Mass Prophylaxis:** It is **never recommended** for cholera as it does not prevent the spread of the epidemic and promotes antibiotic resistance. * **Most Important Treatment:** Rehydration (ORS and IV fluids like Ringer’s Lactate) remains the cornerstone of therapy; antibiotics are secondary. * **Vaccines:** Oral Cholera Vaccines (OCV) like **Dukoral** and **Shanchol** are used for prevention in endemic areas.

Question 1

What is true about the epidemiology of influenza?

Accepted Answer

Extra-human reservoirs are seen.

Answer

Asymptomatic cases are seen rarely.

Answer

The incubation period is 10-12 hours.

Answer

Pandemics are rare.

Question 2

Which index is used to measure the operational efficiency of malaria control programs?

Accepted Answer

Annual Blood Examination Rate (ABER)

Answer

Annual Parasite Incidence (API)

Answer

Infant Parasite Rate

Answer

Spleen Rate

Question 3

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

Accepted Answer

Suture the wound with antibiotic coverage

Answer

Vaccination

Answer

Wash with soap and water

Answer

Administration of antirabies serum and vaccination

Question 4

All of the following are true regarding diphtheria except?

Accepted Answer

Tonsillar membrane can be easily wiped off

Answer

There may be swelling of the neck causing a bull neck appearance

Answer

With a high degree of immunity, a membrane may never appear

Answer

In laryngeal diphtheria, tracheostomy may be needed to relieve respiratory obstruction

Question 5

Under the revised National Tuberculosis Control Programme, what is the schedule of treatment for category I patients?

Accepted Answer

2 HRZE+ 4 HRE

Answer

2 (HRZE)3 + 4(HR)3

Answer

2(HRZES)3 + 1(HRZE)3 + 5(HRE)3

Answer

2(HR)3 + 4 (HR)3

Question 6

Which of the following statements about the composition of the new Oral Rehydration Solution (ORS) is incorrect?

Accepted Answer

Total osmolarity: 300 mmol/L

Answer

Sodium chloride: 2.6 grams/litre

Answer

Potassium chloride: 1.5 grams/litre

Answer

Glucose: 13.5 grams/litre

Question 7

Chemoprophylaxis is indicated for all of the following conditions except?

Accepted Answer

Measles

Answer

Cholera

Answer

Meningococcal meningitis

Answer

Conjunctivitis

Question 8

What is the most important source of infection for meningococci?

Accepted Answer

Carriers

Answer

A case of meningitis

Answer

A subclinical case

Answer

A latent case

Question 9

What is the recommended prophylaxis for cholera?

Accepted Answer

Doxycycline 300mg once daily

Answer

Cephalosporin

Answer

Streptomycin

Answer

Cotrimoxazole

Question 10

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

Accepted Answer

Early diagnosis and treatment

Answer

Isolation of cases

Answer

Specific protection measures

Answer

Elimination of reservoirs

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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