Water Quality and Health — MCQs

10 questions

Which of the following agents causing acute infectious diarrhea can be paired with the pathogenic mechanism of destruction limited to the mature villus cells of small intestine?

In water testing from a well using Horrock's apparatus, blue color appears from the 4th cup onwards. What is the amount of bleaching powder required to disinfect 75000 litres of water?

Which of the following diseases is primarily water-related?

All of the following statements about purification of water are true except:

Which of the following diseases has the largest submerged portion in the iceberg model of disease?

Which method is used to test for chlorine content in drinking water?

An 18-year-old girl presents with watery diarrhea. Most likely causative agent -

Best emergency sanitary measure to control cholera is -

Swajaldhara programme is associated with:

Q10

Horrock's apparatus is used to measure?

Water Quality and Health Indian Medical PG Practice Questions and MCQs

Question 1: Which of the following agents causing acute infectious diarrhea can be paired with the pathogenic mechanism of destruction limited to the mature villus cells of small intestine?

A. Rotavirus (Correct Answer)
B. E. coli
C. Vibrio cholerae
D. Shigella

Explanation: ***Correct: Rotavirus*** - **Rotavirus** infection primarily targets and destroys the mature **villus cells (enterocytes)** at the tips of villi in the small intestine, leading to villus blunting, malabsorption, and secretory diarrhea - The **NSP4 enterotoxin** produced by rotavirus specifically damages mature absorptive cells, resulting in reduced surface area for absorption - This destruction leads to decreased **disaccharidase activity** (particularly lactase), causing osmotic diarrhea from carbohydrate malabsorption - The pathogenic mechanism is **cytolytic destruction limited to mature villus cells**, making this the correct pairing *Incorrect: E. coli* - **Enterotoxigenic E. coli (ETEC)** produces heat-labile (LT) and heat-stable (ST) toxins that stimulate intestinal secretion through cAMP/cGMP pathways **without cellular destruction** - **Enterohemorrhagic E. coli (EHEC)**, particularly O157:H7, produces Shiga toxin that primarily affects the **colon** and causes microvascular damage, not villus cell destruction in the small intestine - **Enteropathogenic E. coli (EPEC)** causes attaching-effacing lesions but affects both mature and immature cells, not selectively mature villus cells *Incorrect: Vibrio cholerae* - **Vibrio cholerae** produces cholera toxin that activates adenylate cyclase in **crypt cells** of the small intestine, leading to massive secretion of fluid and electrolytes [1] - The mechanism is **purely toxin-mediated** with **no cellular destruction** - the epithelium remains intact [1] - Causes profuse watery "rice-water" diarrhea through hypersecretion, not through villus cell damage [1] *Incorrect: Shigella* - **Shigella** species invade and destroy epithelial cells of the **colon** (large intestine), not the small intestine [2], [3] - Causes inflammatory colitis with ulceration, leading to dysentery with bloody diarrhea, mucus, and pus [3] - The pathogenic mechanism involves **bacterial invasion, intracellular multiplication**, and **inflammatory response** - distinct from selective mature villus cell destruction in the small intestine [3] **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Gastrointestinal Tract, pp. 792-793. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Gastrointestinal Tract, p. 793. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Gastrointestinal Tract, pp. 794-795.

Question 2: In water testing from a well using Horrock's apparatus, blue color appears from the 4th cup onwards. What is the amount of bleaching powder required to disinfect 75000 litres of water?

A. 1600 gm
B. 2000 gm
C. 1300 gm
D. 100 gm (Correct Answer)

Explanation: ***100 gm*** - In **Horrock's apparatus** test, blue color appearing from the 4th cup indicates a **chlorine demand of 0.4 ppm (0.4 mg/L)** for the water sample. - **Total chlorine required** = 0.4 mg/L × 75,000 L = **30,000 mg = 30 gm** of pure chlorine. - Standard bleaching powder contains **30% available chlorine**, so: **Bleaching powder needed = 30 gm ÷ 0.30 = 100 gm**. - This is the scientifically accurate amount for disinfecting 75,000 liters of water with 0.4 ppm chlorine demand. *1000 gm* - This represents a **10-fold excess** over the actual requirement of 100 gm based on the measured chlorine demand. - Using 1000 gm would result in severe **over-chlorination** (4 ppm instead of 0.4 ppm), causing strong unpleasant taste, odor, and potential health concerns. *1600 gm* - This amount represents **16 times the required dose**, leading to dangerously high chlorine levels in the water. - Such excessive chlorination would make the water unpalatable and potentially toxic to consumers. *2000 gm* - This represents a **20-fold excess**, providing extreme and harmful over-disinfection. - Such excessive amounts could lead to **chlorine toxicity** and would be wasteful and harmful to consumers. *1300 gm* - This amount exceeds the calculated requirement by **13 times**, providing unnecessary and harmful over-disinfection. - The precise calculation based on **0.4 ppm chlorine demand** and **75,000 L volume** yields exactly **100 gm**, not 1300 gm.

Question 3: Which of the following diseases is primarily water-related?

A. Scabies
B. Yellow fever
C. Cholera (Correct Answer)
D. Dysentery

Explanation: ***Cholera*** - Cholera is caused by the bacterium **Vibrio cholerae**, which is typically transmitted through the consumption of **contaminated water or food**. - This disease is a classic example of a **waterborne illness**, with outbreaks often linked to inadequate sanitation and unsafe drinking water. *Yellow fever* - Yellow fever is a **viral hemorrhagic disease** transmitted by infected **mosquitoes**, primarily Aedes aegypti. - While mosquitoes may breed in water, the disease itself is not directly transmitted through water consumption. *Scabies* - Scabies is a **skin infestation** caused by the mite **Sarcoptes scabiei**, which burrows into the outer layer of the skin. - Transmission occurs through **direct, prolonged skin-to-skin contact**, not through water. *Dysentery* - Dysentery is an **intestinal inflammation** causing bloody diarrhea, which can be caused by bacteria (e.g., Shigella) or amoebas (e.g., Entamoeba histolytica). - Although it can be transmitted through contaminated water or food, it is a broader term for a symptom, and **cholera is more exclusively and primarily focused on water-borne transmission mechanisms**.

Question 4: All of the following statements about purification of water are true except:

A. Sodium thiosulphate is used to neutralize residual chlorine in water samples
B. Coliforms must not be detectable in any 100 ml sample of drinking water
C. Coliforms may be detected by multiple tube method and indole production
D. Presence of Clostridial spores indicates recent contamination of water (Correct Answer)

Explanation: ***Presence of Clostridial spores indicates recent contamination of water*** - The presence of **Clostridial spores** indicates **remote or intermittent contamination**, not recent contamination, because these spores can survive in water for extended periods due to their resistance to environmental stressors and disinfectants. - While Clostridia are indicators of fecal contamination, their spores' longevity means they do not pinpoint the timing of contamination as precisely as **coliforms** or **E. coli**. *Sodium thiosulphate is used to neutralize residual chlorine in water samples* - **Sodium thiosulfate** is used in water microbiology testing to **neutralize residual chlorine** in collected water samples, preventing further disinfection action during laboratory analysis. - It effectively stops the bactericidal action of chlorine, which could otherwise continue to kill bacteria in the sample after collection, leading to false negative results for **microbial contaminants**. - This is a **laboratory procedure** for accurate microbial testing, not a water purification method itself. *Coliforms must not be detectable in any 100 ml sample of drinking water* - This statement accurately reflects the widely accepted standard for potable water quality, where **drinking water** should be **free of coliform bacteria** to ensure its safety for consumption. - The detection of any coliforms in a 100 ml sample indicates potential fecal contamination and the possible presence of pathogenic microorganisms. *Coliforms may be detected by multiple tube method and indole production* - The **multiple tube fermentation (MTF) method**, also known as the most probable number (MPN) method, is a standard technique for detecting and quantifying **coliforms** in water. - Indole production is a biochemical test particularly useful for confirming the presence of **Escherichia coli** (a type of fecal coliform), as E. coli typically produces indole from tryptophan.

Question 5: Which of the following diseases has the largest submerged portion in the iceberg model of disease?

A. Influenza (Correct Answer)
B. Chickenpox
C. Tetanus
D. Rabies

Explanation: **The Iceberg Model of Disease** represents the concept that for many diseases, only a small portion of cases (the "tip" above water) are clinically apparent and reported, while a much larger portion (the "submerged" part) consists of asymptomatic, subclinical, or undiagnosed cases. ***Influenza*** - Has the **largest submerged portion** among the given options, with **50-75% of infections being asymptomatic or mild** and going undiagnosed - High transmissibility and varied clinical presentation contribute to significant hidden burden - Only severe cases requiring hospitalization typically get reported, representing just the "tip of the iceberg" - Classic example of diseases with large subclinical-to-clinical ratio *Chickenpox* - Most cases are **clinically apparent** with characteristic vesicular rash - Asymptomatic infections are rare due to distinctive clinical features - High visibility of cases reduces the submerged portion significantly *Tetanus* - **Severe, acute neurological condition** with distinct clinical manifestations (trismus, risus sardonicus, opisthotonus) - Almost all cases are diagnosed due to dramatic presentation - Virtually no submerged portion - what exists clinically is recognized *Rabies* - **Nearly uniformly fatal** once symptoms appear, making all symptomatic cases clinically evident - No asymptomatic or mild phase after symptom onset - Minimal to no submerged portion in the iceberg model

Question 6: Which method is used to test for chlorine content in drinking water?

A. Turbidity test
B. Jar test
C. Orthotolidine test (Correct Answer)
D. Coliform test

Explanation: ***Orthotolidine test*** - The **orthotolidine test** specifically reacts with chlorine (both free and combined forms) in water to produce a distinct yellow color, the intensity of which can be measured to determine chlorine concentration. - This method is a standard, **colorimetric procedure** widely used for routine monitoring of chlorine residuals in drinking water. *Turbidity test* - A **turbidity test** measures the cloudiness or haziness of a fluid caused by suspended particles, indicating water clarity. - It does not directly measure the presence or concentration of **chlorine**. *Jar test* - The **jar test** is a laboratory procedure used to simulate and optimize coagulation-flocculation processes in water treatment. - It helps determine optimal chemical dosages for removing suspended solids but does not directly test for **chlorine content**. *Coliform test* - The **coliform test** is used to detect the presence of coliform bacteria, which are indicators of potential fecal contamination in water. - This test is a measure of **microbiological quality** and is unrelated to chlorine concentration.

Question 7: An 18-year-old girl presents with watery diarrhea. Most likely causative agent -

A. Rotavirus
B. V. cholerae (Correct Answer)
C. Salmonella
D. Shigella

Explanation: ***V. cholerae*** - *Vibrio cholerae* is a classic cause of **acute, severe watery diarrhea** that can lead to rapid dehydration. - While other agents can cause watery diarrhea, *V. cholerae* is primarily associated with large-scale outbreaks of this symptom. *Rota virus* - While rotavirus causes **watery diarrhea**, it primarily affects **infants and young children** and is less common as the most likely cause in an 18-year-old in many settings due to widespread vaccination programs. - The diarrhea, though watery, is often accompanied by **fever and vomiting**. *Salmonella* - *Salmonella* typically causes **inflammatory diarrhea** (dysentery-like symptoms with blood/mucus in stool) or **food poisoning**, with diarrhea that may be watery but is often not as profuse or severe as cholera. - It is more commonly associated with **fever and abdominal cramps**. *Shigella* - *Shigella* causes **bacillary dysentery**, characterized by **bloody, mucoid stools**, abdominal cramps, and fever. - It is not typically associated with solely profuse watery diarrhea.

Question 8: Best emergency sanitary measure to control cholera is -

A. Chemoprophylaxis
B. Mass vaccination
C. Disinfection of stool
D. Provision of chlorinated water (Correct Answer)

Explanation: ***Provision of chlorinated water*** - Cholera is primarily a **waterborne disease**, and providing safe, chlorinated water is the most effective way to prevent its transmission in an emergency. - **Chlorination** kills *Vibrio cholerae* in water sources, significantly reducing the risk of infection. *Chemoprophylaxis* - While it can be used for close contacts or specific high-risk groups, **mass chemoprophylaxis** is not a sustainable or practical emergency measure for controlling widespread cholera outbreaks. - It carries risks of **antibiotic resistance** and doesn't address the underlying environmental source of contamination. *Mass vaccination* - **Oral cholera vaccines** are effective, but their deployment in an emergency is often challenged by logistics, time constraints, and the need for multiple doses, making it less immediate than securing safe water. - Vaccination provides **individual protection** but does not rapidly contain an ongoing outbreak if environmental sources of contamination persist. *Disinfection of stool* - **Disinfection of stool** from infected individuals is crucial for preventing local spread and protecting caregivers, but it does not address the broader community-level contamination of water sources. - This measure targets the **secondary transmission** route rather than the primary environmental reservoir.

Question 9: Swajaldhara programme is associated with:

A. Provision of safe drinking water (Correct Answer)
B. Provision of food supplements for destitute women
C. Provision of relief for victim of sexual abuse
D. Provision of health care for sick tribals

Explanation: ***Provision of safe drinking water*** - The **Swajaldhara programme** was launched by the Government of India in 2002 to accelerate coverage of **drinking water supply** in rural areas - Its primary objective was to ensure access to **safe and sustainable drinking water sources** through community participation and decentralized management - The program emphasized local ownership with communities contributing 10% of project costs *Provision of food supplements for destitute women* - Food security programs for women fall under separate social welfare schemes like ICDS and PDS - The **Swajaldhara programme** was specifically focused on **water supply infrastructure**, not nutrition *Provision of relief for victim of sexual abuse* - Relief for victims of sexual abuse is addressed through **justice and women's safety initiatives** (e.g., One Stop Centres, Nirbhaya Fund) - This is unrelated to the water supply mandate of Swajaldhara *Provision of health care for sick tribals* - Health care for tribal populations is managed through dedicated programs under the Ministry of Health and Family Welfare - Swajaldhara's scope was limited to **rural drinking water infrastructure**, not healthcare delivery

Question 10: Horrock's apparatus is used to measure?

A. Wind velocity
B. Humidity
C. Chlorine demand (Correct Answer)
D. Cooling power

Explanation: ***Chlorine demand*** - Horrock's apparatus is specifically designed for determining the **chlorine demand** of water, which is the amount of **chlorine** consumed by impurities before a **free chlorine residual** is established. - This apparatus is crucial in **water treatment processes** to ensure effective **disinfection** by adjusting chlorine dosages. *Wind velocity* - **Wind velocity** is typically measured using an **anemometer**, a device with rotating cups or a propeller that spins in response to wind. - Horrock's apparatus has no components or mechanisms for detecting or quantifying wind movement. *Humidity* - **Humidity** is measured by instruments such as **hygrometers** or **psychrometers**, which assess the amount of water vapor in the air. - These devices utilize properties like **condensation** or changes in **electrical resistance**, which are unrelated to the function of Horrock's apparatus. *Cooling power* - **Cooling power** refers to the rate at which heat can be removed from a system and is measured using devices like **catathermometers** or specialized **calorimeters**. - Horrock's apparatus is a **chemical testing device** and does not have the capability to measure thermal properties or cooling rates.

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