Infectious Diseases Practice Questions

Q: What is the period of isolation for Salmonella infection?

3 consecutive stool cultures are negative. ### Explanation The correct answer is **C: 3 consecutive stool cultures are negative.** **Why it is correct:** Salmonella (specifically *Salmonella Typhi* and *Paratyphi*) is primarily transmitted via the fecal-oral route. Clinical recovery does not always coincide with the cessation of pathogen shedding. To ensure a patient is no longer infectious and to prevent the development of a "carrier state," public health guidelines require microbiological evidence of clearance. Isolation or exclusion from high-risk activities (like food handling) is maintained until **three consecutive stool cultures**, taken at least 24 hours apart, are negative. **Analysis of Incorrect Options:** * **A. 72 hours after chemotherapy:** While symptoms may improve shortly after starting antibiotics (chemotherapy), the patient can still shed the bacteria in feces, posing a transmission risk. * **B. Widal test negative:** The Widal test measures antibodies (H and O agglutinins), not the presence of the bacteria itself. Titers can remain high long after the infection has cleared, making it an invalid tool for determining the end of isolation. * **D. Urine culture is negative twice:** While *S. Typhi* can be found in urine (especially in cases associated with Schistosomiasis), stool culture is the gold standard for confirming the end of the communicable period. **High-Yield Facts for NEET-PG:** * **Carrier State:** Defined as the excretion of *S. Typhi* in stool/urine for **more than one year**. * **Chronic Carrier Site:** The **Gallbladder** is the most common site for chronic fecal carriage (often associated with gallstones). * **Urinary Carrier Site:** Associated with **Schistosoma haematobium** infection in the bladder. * **Culture Timing:** Stool cultures are most likely to be positive in the **2nd and 3rd weeks** of illness, whereas blood cultures are best in the **1st week**.

Q: What is the primary method for the control of tuberculosis and leprosy?

Early diagnosis and treatment. **Explanation:** The primary strategy for controlling chronic infectious diseases like Tuberculosis (TB) and Leprosy is **Early Diagnosis and Treatment**. This approach is based on the epidemiological principle of **Secondary Prevention**, which aims to halt disease progression in the individual and reduce the "pool of infection" in the community. 1. **Why Option C is Correct:** Both TB and Leprosy have long incubation periods and are transmitted via prolonged contact. By identifying cases early (via sputum microscopy/NAAT for TB or skin examination for Leprosy) and initiating prompt chemotherapy (DOTS for TB; MDT for Leprosy), the patient rapidly becomes non-infectious. This breaks the chain of transmission, effectively controlling the spread. 2. **Why Other Options are Incorrect:** * **Isolation (A):** Historically used (Sanatoriums), but no longer practical or necessary. Modern chemotherapy renders patients non-infectious within days to weeks, making home-based treatment the standard. * **Specific Protection (B):** While the BCG vaccine exists, its efficacy in preventing adult pulmonary TB is variable, and there is no primary vaccine for Leprosy (though BCG offers some cross-protection). Thus, it is not the *primary* control method. * **Elimination of Reservoirs (D):** Humans are the only significant reservoir for both diseases. "Elimination" of the reservoir would mean curing every single case; therefore, early diagnosis and treatment is the *tool* used to achieve this goal. **High-Yield Clinical Pearls for NEET-PG:** * **TB:** The goal of the National TB Elimination Program (NTEP) is to end TB by **2025** in India. * **Leprosy:** A case is "released from treatment" (RFT) after completing MDT. The main indicator for leprosy control is the **New Case Detection Rate (NCDR)**. * **Key Concept:** For most communicable diseases without an effective mass vaccine, **Case Finding** is the backbone of control.

Q: What is the recommended concentration of anhydrous glucose in ORS for reduced osmolarity?

13.5 gm/L. ### Explanation The correct answer is **13.5 gm/L**. **1. Underlying Medical Concept:** The World Health Organization (WHO) and UNICEF shifted from the standard ORS to **Low Osmolarity ORS** to reduce the risk of hypernatremia and decrease the need for unscheduled IV fluids. The physiological basis of ORS is the **sodium-glucose cotransport** mechanism in the small intestine. For optimal absorption, glucose and sodium must be present in a specific ratio. In the reduced osmolarity formulation, the concentration of **Anhydrous Glucose is 13.5 gm/L**, which contributes 75 mmol/L to the total osmolarity (245 mOsm/L). **2. Analysis of Options:** * **Option A (26 gm/L):** This was the glucose concentration in the **Old (Standard) WHO ORS**. It resulted in a higher total osmolarity (311 mOsm/L), which sometimes led to osmotic diarrhea. * **Option B (2.9 gm/L):** This is the concentration of **Trisodium Citrate** in the current low osmolarity ORS. * **Option C (13.5 gm/L):** Correct. This is the anhydrous glucose concentration for the current WHO-recommended formula. * **Option D (1.5 gm/L):** This is the concentration of **Potassium Chloride** in the current ORS formula. **3. High-Yield Clinical Pearls for NEET-PG:** * **Total Osmolarity of New ORS:** 245 mOsm/L (Sodium: 75, Chloride: 65, Glucose: 75, Potassium: 20, Citrate: 10). * **Sodium Concentration:** Reduced from 90 mEq/L (Old) to **75 mEq/L** (New). * **Benefits of Low Osmolarity ORS:** Reduces stool output by 20%, reduces vomiting by 30%, and reduces the need for IV fluids by 33%. * **Re-Somal:** A special ORS for severely malnourished children (SAM) with lower sodium (45 mmol/L) and higher potassium (40 mmol/L).

Q: Which of the following statements regarding diphtheria carriers is incorrect?

Immunization effectively prevents the carrier state.. ### Explanation The core concept to understand in Diphtheria epidemiology is the difference between **antitoxic immunity** and **antibacterial immunity**. **1. Why Option A is the Correct Answer (Incorrect Statement):** Diphtheria vaccine (DPT/Pentavalent) contains **Diphtheria Toxoid**. This induces the production of antibodies against the *toxin* (exotoxin) produced by *Corynebacterium diphtheriae*, not against the bacterium itself. Therefore, while immunization protects the individual from the clinical disease (toxemia), it **does not prevent the colonization** of the bacteria in the nasopharynx. Consequently, a fully vaccinated individual can still become a carrier and harbor the organism. **2. Analysis of Other Options:** * **Option B:** This is a factual statement. While nasal carriers exist, **faucial (throat) carriers** are considered much more dangerous and effective at spreading the disease through respiratory droplets. * **Option C:** Prophylaxis is a standard public health measure. Contacts of a carrier should receive a booster dose of toxoid and a course of antibiotics (Erythromycin or Penicillin) to eradicate the carrier state and prevent further spread. * **Option D:** In an endemic setup, carriers outnumber clinical cases (ratio of roughly 95:5). They act as a hidden **reservoir** in the community, making them a primary source of transmission. ### High-Yield Clinical Pearls for NEET-PG: * **Incubation Period:** 2–6 days. * **Schick Test:** Used to detect the immune status of an individual (susceptibility). * **Carrier Treatment:** The drug of choice for treating a carrier is **Erythromycin** (more effective than Penicillin for clearing the carrier state). * **Control:** A carrier is considered "cleared" only after **two consecutive negative cultures** from the nose and throat, taken 24 hours apart.

Q: Leprosy is not yet eradicated because of which of the following reasons?

Long incubation period. **Explanation:** The primary reason leprosy remains a challenge for global eradication is its **long incubation period**, which typically ranges from **3 to 5 years** (can extend up to 20 years). This prolonged "silent" phase means that an infected individual can remain asymptomatic for years while potentially contributing to the transmission chain. By the time clinical symptoms appear and the patient is diagnosed, they may have already infected several close contacts, making it difficult to map and break the transmission cycle effectively. **Analysis of Options:** * **A. Absence of an effective vaccine:** While there is no specific "leprosy vaccine," the **BCG vaccine** provides significant cross-protection (approx. 50%) against *M. leprae*. While a more potent vaccine would help, the long incubation period is a more fundamental barrier to eradication. * **B. High infectivity with low pathogenicity:** This is actually a characteristic of leprosy (high infectivity but low virulence/pathogenicity). However, this usually favors control efforts because most people exposed do not develop the disease. It is the *latency*, not the infectivity pattern, that hinders eradication. * **C. Humans are the only reservoir:** This is generally true (though armadillos are a minor zoonotic source in the Americas). If humans were the *only* reservoir, it would actually make eradication **easier** (similar to Smallpox), not harder. **NEET-PG High-Yield Pearls:** * **Causative Agent:** *Mycobacterium leprae* (Acid-fast, obligate intracellular, grows best at 30°C). * **Elimination vs. Eradication:** Leprosy was "eliminated" as a public health problem (defined as <1 case per 10,000 population) globally in 2000, but **eradication** (zero cases) is not yet achieved. * **Most Infectious Form:** Multibacillary (lepromatous) leprosy. * **First Sign:** Usually a pale or reddish patch with loss of sensation.

Q: Chander's index is defined as?

No. Of eggs / gm of stool. ### Explanation **Chander’s Index** is a classic epidemiological tool used to estimate the **intensity of Hookworm infection** (Ancylostomiasis) in a community. It is defined as the **average number of eggs per gram (EPG) of stool** across a surveyed population. #### Why Option A is Correct: The index relies on the quantitative estimation of helminthic eggs. By calculating the mean number of eggs per gram of stool, public health officials can categorize the severity of the infection in a locality. * **Index 250:** Indicates a significant public health problem where clinical hookworm disease (anemia) is likely prevalent. #### Why Other Options are Incorrect: * **Options B & C:** These refer to **larvae**. Hookworm diagnosis in stool is primarily based on detecting eggs (using techniques like Kato-Katz). Larvae are typically seen only if the stool sample is old or cultured (e.g., Harada-Mori culture), making them an unreliable metric for a standardized index. * **Option D:** The standard unit for helminthic egg counting in international public health (and the Kato-Katz method) is **per gram** of feces, not per 100g. Using 100g would result in unnecessarily large numbers and is not the conventional denominator for Chander’s Index. #### High-Yield Clinical Pearls for NEET-PG: * **Hookworm Species:** *Ancylostoma duodenale* (consumes ~0.15 ml blood/day) and *Necator americanus* (consumes ~0.03 ml blood/day). * **Clinical Hallmark:** Iron deficiency anemia (Microcytic Hypochromic). * **Ground Itch:** A local dermatitis caused by the entry of **L3 (Filariform) larvae**, which is the infective stage. * **Other Indices:** Do not confuse this with the **Breteau Index** (used for Aedes mosquitoes/Dengue) or the **Spleen Rate** (used for Malaria).

Q: Which of the following is an emerging infection in India?

Chikungunya. **Explanation:** **Emerging infections** are defined as infections that have newly appeared in a population or have existed but are rapidly increasing in incidence or geographic range. **Chikungunya (Option A)** is the correct answer because it fits the definition of a re-emerging/emerging infection in India. After a long period of quiescence since the 1970s, India witnessed a massive outbreak in 2006 affecting several states. Since then, it has established a persistent presence with periodic outbreaks, driven by the widespread distribution of its vectors, *Aedes aegypti* and *Aedes albopictus*. **Analysis of Incorrect Options:** * **Hanta virus (Option B):** While sporadic cases or serological evidence may exist, it is not classified as a major emerging public health threat in the Indian context compared to Chikungunya. * **Ebola virus (Option C):** This is an exotic pathogen. While there is a risk of importation, there has been no established transmission or "emergence" of Ebola within the Indian population. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Primarily *Aedes aegypti* (day biter). * **Hallmark Symptom:** Severe, often debilitating joint pain (arthralgia) which can persist for months (chronic stage), distinguishing it from Dengue. * **Incubation Period:** Typically 3–7 days. * **Diagnosis:** ELISA for IgM antibodies (after 5 days) or RT-PCR (during the first few days of viremia). * **Other Emerging/Re-emerging diseases in India:** Dengue, Japanese Encephalitis, Kyasanur Forest Disease (KFD), Nipah virus, and Scrub Typhus.

Q: Which of the following is NOT included in the Revised National Tuberculosis Control Programme (RNTCP)?

Active case finding. The RNTCP (now renamed the **National TB Elimination Programme - NTEP**) is primarily based on the **DOTS strategy**, which emphasizes **Passive Case Finding**. This means the program relies on symptomatic patients voluntarily reporting to health facilities rather than health workers searching for cases in the community. ### Why "Active Case Finding" is the Correct Answer: Under standard RNTCP/NTEP guidelines, the core strategy is passive case finding to ensure that those with symptoms (cough >2 weeks) are diagnosed. While active case finding (ACF) is conducted in specific high-risk vulnerable populations (e.g., slums, prisons), it is **not** the primary diagnostic strategy of the program. ### Explanation of Other Options: * **X-ray is diagnostic:** Under the updated NTEP algorithms, Chest X-ray is used as a primary screening tool. If the X-ray is suggestive of TB, the patient is then subjected to molecular testing (CBNAAT/Truenat) for confirmation. * **Directly observed treatment:** This remains a pillar of the program. A treatment supporter ensures the patient swallows the medication to prevent default and drug resistance. * **Drugs given daily:** Since 2017, the RNTCP shifted from intermittent (thrice weekly) regimens to **Daily Regimens** using Fixed-Dose Combinations (FDCs) to maintain higher peak plasma concentrations. ### High-Yield Pearls for NEET-PG: * **Diagnosis:** The "Gold Standard" for diagnosis in NTEP is now **Molecular Tests (CBNAAT/Truenat)**, not sputum microscopy. * **Goal:** India aims to **Eliminate TB by 2025**, five years ahead of the global SDG target of 2030. * **Nikshay Poshan Yojana:** Provides ₹500/month nutritional support to all TB patients. * **Definition of Elimination:** < 1 case per 1,000,000 (1 million) population.

Question 1

What is the period of isolation for Salmonella infection?

Accepted Answer

3 consecutive stool cultures are negative

Answer

72 hours after chemotherapy

Answer

Widal test negative

Answer

Urine culture is negative twice

Question 2

What is the primary method for the control of tuberculosis and leprosy?

Accepted Answer

Early diagnosis and treatment

Answer

Isolation of cases

Answer

Specific protection

Answer

Elimination of reservoirs

Question 3

What is the recommended concentration of anhydrous glucose in ORS for reduced osmolarity?

Accepted Answer

13.5 gm/L

Answer

26 gm/l

Answer

2.9 gm/L

Answer

1.5 gm/L

Question 4

Which of the following statements regarding diphtheria carriers is incorrect?

Accepted Answer

Immunization effectively prevents the carrier state.

Answer

Nasal carriers pose minimal risk of transmission.

Answer

Prophylactic treatment for contacts of carriers is essential.

Answer

Diphtheria carriers are a significant source of disease transmission.

Question 5

All of the following are true about varicella EXCEPT?

Accepted Answer

Period of communicability is 2 days after the last vesicle has crusted.

Answer

All stages of the rash are typically seen at the same time.

Answer

Secondary attack rate in susceptible individuals is approximately 90%.

Answer

Rash commonly appears in the flexor areas.

Question 6

Under the National Malaria Eradication Programme (NMEP), what is the function of fever depot treatment?

Accepted Answer

Collection of slides and treatment of fever

Answer

Diagnosis of cases and spraying

Answer

Treatment of fever cases only

Answer

Treatment, slide collection, and spraying

Question 7

Leprosy is not yet eradicated because of which of the following reasons?

Accepted Answer

Long incubation period

Answer

Absence of an effective vaccine

Answer

High infectivity with low pathogenicity

Answer

Humans are the only reservoir

Question 8

Chander's index is defined as?

Accepted Answer

No. Of eggs / gm of stool

Answer

No. Of larvae / 100g of stool

Answer

No. Of larvae / gm of stool

Answer

No. Of eggs / 100g of stool

Question 9

Which of the following is an emerging infection in India?

Accepted Answer

Chikungunya

Answer

Hanta virus

Answer

Ebola virus

Answer

None of the above

Question 10

Which of the following is NOT included in the Revised National Tuberculosis Control Programme (RNTCP)?

Accepted Answer

Active case finding

Answer

X-ray is diagnostic

Answer

Directly observed treatment

Answer

Drugs given daily

Infectious Diseases — MCQs

Infectious Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?