Water-Borne Diseases — MCQs
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 frequent traveler presented with 4 days of continuous fever, abdominal pain, and bradycardia. What is the best diagnostic test to confirm the pathogen?
All of the following are helminthic waterborne disease except?
Which disease is characterized by severe watery diarrhea and is associated with a toxin-producing bacterium?
A 17 year old adolescent, presented with fever since one week which is step-ladder in pattern. He also has loose stools which are "pea-soup" in consistency. Rose spots are seen on his body. He is most probably infected with:
What is the name of the defluoridation process of drinking water developed by the NEERI?
Which of the following pathogens are associated with watery diarrhea after an incubation period of 8 to 14 hours?
A person returns to Delhi from Bangladesh after 2 days and has diarrhea. Stool examination shows RBC's in stool. The likely organism causing is ?
All are zoonotic disease except -
All following are at-risk group adults meriting Hepatitis B vaccination in low endemic areas except for which of the following?
Water-Borne Diseases Indian Medical PG Practice Questions and MCQs
Question 1: 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 2: A frequent traveler presented with 4 days of continuous fever, abdominal pain, and bradycardia. What is the best diagnostic test to confirm the pathogen?
- A. Widal test
- B. Blood culture (Correct Answer)
- C. Urine culture
- D. Stool culture
Explanation: ***Blood culture*** - **Blood culture** is the most sensitive and specific test for confirming **typhoid fever** in the first week of illness. - The presence of **continuous fever** (step-ladder pattern), **abdominal pain**, and **relative bradycardia** in a traveler strongly suggests typhoid fever caused by *Salmonella Typhi*. *Widal test* - The **Widal test** detects antibodies against *Salmonella Typhi* antigens and is often positive later in the disease course. - It has **limited sensitivity and specificity**, especially in endemic areas or with prior vaccination, leading to false positives and negatives. *Urine culture* - **Urine culture** has a low yield for *Salmonella Typhi*, as bacteria are intermittently shed in urine, usually later in the disease. - It's primarily useful for diagnosing **urinary tract infections** or in chronic carriers of typhoid. *Stool culture* - **Stool culture** yield is higher in the later stages of typhoid fever, as *Salmonella Typhi* is shed in feces. - Its sensitivity is lower than blood culture in the early acute phase when bacteremia is most prominent.
Question 3: All of the following are helminthic waterborne disease except?
- A. Hydatid cyst
- B. Roundworm
- C. Giardiasis (Correct Answer)
- D. Threadworm
Explanation: ***Giardiasis*** - **Giardiasis** is caused by the **protozoan parasite** *Giardia lamblia*, not a helminth. - It is a true waterborne disease, transmitted through contaminated water. - This is the correct answer as it is NOT a helminthic infection. *Hydatid cyst* - **Hydatid cyst disease** is caused by the larval stage of the **tapeworm** *Echinococcus granulosus*, a helminth. - Primarily transmitted through ingestion of eggs from dog feces (zoonotic), though contaminated water can occasionally serve as a vehicle. *Roundworm* - **Roundworm infection** (ascariasis) is caused by the nematode *Ascaris lumbricoides*, a helminth. - Classified as a soil-transmitted helminth (STH), acquired through ingestion of eggs from contaminated soil; water can occasionally act as a transmission vehicle. *Threadworm* - **Threadworm infection** (enterobiasis/pinworm) is caused by the nematode *Enterobius vermicularis*, a helminth. - Primarily transmitted person-to-person via the fecal-oral route through contaminated hands and fomites; water transmission is uncommon but possible in poor sanitation conditions.
Question 4: Which disease is characterized by severe watery diarrhea and is associated with a toxin-producing bacterium?
- A. Gastroenteritis
- B. Cholera (Correct Answer)
- C. Dysentery
- D. Typhoid fever
Explanation: ***Cholera*** - Cholera is known for causing **severe, watery diarrhea** (often described as "rice water stools") due to the action of **cholera toxin** produced by *Vibrio cholerae* [1], [2]. - The toxin stimulates excessive fluid and electrolyte secretion in the small intestine, leading to rapid **dehydration** and electrolyte imbalance [2]. *Gastroenteritis* - This is a general term for **inflammation of the stomach and intestines**, which can be caused by various pathogens (viruses, bacteria, parasites) and toxins. - While it often presents with diarrhea, it doesn't specifically imply the **severe watery diarrhea** linked to a specific toxin as seen in cholera. *Dysentery* - Dysentery is characterized by **bloody diarrhea**, often accompanied by **fever and abdominal cramps**, indicating inflammation and damage to the intestinal lining [3]. - It is typically caused by bacteria like *Shigella* or *entamoeba histolytica*, distinct from the purely watery diarrhea of cholera [3]. *Typhoid fever* - Typhoid fever is a systemic illness caused by *Salmonella typhi*, characterized by **sustained fever, headache, malaise**, and can include **constipation or mild diarrhea**. - It does not primarily present with **severe watery diarrhea** induced by a specific toxin, unlike cholera.
Question 5: A 17 year old adolescent, presented with fever since one week which is step-ladder in pattern. He also has loose stools which are "pea-soup" in consistency. Rose spots are seen on his body. He is most probably infected with:
- A. Salmonella typhi (Correct Answer)
- B. Adenovirus
- C. Rotavirus
- D. Vibrio cholerae
Explanation: ***Salmonella typhi*** - The combination of **step-ladder fever**, **"pea-soup" diarrhea**, and **rose spots** is a classic presentation of **typhoid fever**, caused by *Salmonella typhi* [1]. - This bacterial infection predominantly affects the gastrointestinal tract and can lead to systemic symptoms [1]. *Adenovirus* - **Adenovirus** typically causes **respiratory tract infections**, **conjunctivitis**, or **gastroenteritis**, but not with the specific symptom profile of step-ladder fever or rose spots. - While it can cause diarrhea, it's usually not described as "pea-soup" and lacks the other systemic features. *Rotavirus* - **Rotavirus** is a common cause of **severe gastroenteritis** in infants and young children, characterized by **watery diarrhea** and vomiting. - It does not present with step-ladder fever or rose spots, which are pathognomonic for typhoid. *Vibrio cholerae* - **Vibrio cholerae** causes **cholera**, an acute diarrheal illness characterized by **profuse watery diarrhea** (often described as "rice-water stools") and rapid dehydration. - It does not typically cause step-ladder fever or skin manifestations like rose spots.
Question 6: What is the name of the defluoridation process of drinking water developed by the NEERI?
- A. Activated sludge process
- B. Recarbonation process
- C. Nalgonda process (Correct Answer)
- D. Double pot method
Explanation: ***Nalgonda process*** - The **Nalgonda technique** is a defluoridation method developed by the **National Environmental Engineering Research Institute (NEERI)** in India. - It utilizes **aluminum salts**, **lime**, and **bleaching powder** for fluoride removal through precipitation and adsorption. *Activated sludge process* - This is a **wastewater treatment method** that uses microorganisms to consume organic pollutants, primarily for sewage treatment, not defluoridation. - It involves aeration of wastewater with a flocculated biological growth of bacteria and other microorganisms. *Recarbonation process* - **Recarbonation** is a step in **water softening**, specifically after lime-soda ash treatment, to lower the pH and stabilize the water by converting excess calcium hydroxide to calcium carbonate. - It is used to prevent scale formation and is not a defluoridation method. *Double pot method* - The **double pot method** is a technique for **household water purification**, often used in rural areas, that typically involves filtration and disinfection, but not specific defluoridation. - It usually consists of two pots, one placed inside the other, with a filter medium or coagulant treatment.
Question 7: Which of the following pathogens are associated with watery diarrhea after an incubation period of 8 to 14 hours?
- A. Rotavirus and Norwalk virus
- B. Shigella and Salmonella
- C. S. aureus and Bacillus cereus
- D. Bacillus cereus and Clostridium perfringens (Correct Answer)
Explanation: **Bacillus cereus and Clostridium perfringens** - Both *Bacillus cereus* diarrheal type and *Clostridium perfringens* are known to cause **watery diarrhea** after an incubation period of **8 to 14 hours**. - This longer incubation period is typical for toxins produced in the gut after ingestion of spores or large numbers of bacteria. *Rotavirus and Norwalk virus* - **Rotavirus** typically has an incubation period of 1-3 days and causes **severe watery diarrhea**, especially in infants and young children. - **Norwalk virus** (norovirus) usually has an incubation period of 12-48 hours and causes **acute gastroenteritis** with vomiting and watery diarrhea. *Shigella and Salmonella* - **Shigella** causes **dysentery** (bloody diarrhea) with a shorter incubation period (1-2 days) rather than watery diarrhea. - **Salmonella** can cause **inflammatory diarrhea** (salmonellosis) with an incubation period ranging from 6 hours to 6 days, often shorter than 8-14 hours for typical infections. *S. aureus and Bacillus cereus* - **Staphylococcus aureus** causes vomiting and diarrhea due to preformed toxin, with a very short incubation period of **1-6 hours**. - While *Bacillus cereus* can cause emetic (vomiting) or diarrheal type illness, the emetic form has a 1-6 hour incubation period, which is not consistent with the 8-14 hour window.
Question 8: A person returns to Delhi from Bangladesh after 2 days and has diarrhea. Stool examination shows RBC's in stool. The likely organism causing is ?
- A. Enteropathogenic E. Coli
- B. Salmonella typhi
- C. Enterotoxigenic E. Coli
- D. Shigella dysenteriae (Correct Answer)
Explanation: ***Shigella dysenteriae*** - This organism causes **bacillary dysentery**, characterized by fever, abdominal cramps, and frequent, small-volume stools containing **blood and mucus (RBCs)**, which fits the clinical picture of a traveler experiencing diarrhea with RBCs in stool. - The rapid onset (within 2 days of return) and the presence of **RBCs in stool** are highly suggestive of an invasive bacterial pathogen like *Shigella*. *Enteropathogenic E. Coli* - **EPEC** typically causes **watery diarrhea**, particularly in infants, by disrupting intestinal microvilli. - It does **not usually cause bloody stools** or significant red blood cells in the stool. *Salmonella typhi* - While *Salmonella typhi* causes **typhoid fever**, its initial presentation is typically with fever, headache, and constipation, followed by a **pea-soup diarrhea** in later stages, which is usually not bloody. - The rapid onset of bloody diarrhea within 2 days is less characteristic of typhoid fever, which has a longer incubation period. *Enterotoxigenic E. Coli* - **ETEC** is a common cause of **traveler's diarrhea**, but it produces toxins that lead to **watery, non-bloody diarrhea**. - The presence of **RBCs in the stool** makes ETEC an unlikely cause in this scenario.
Question 9: All are zoonotic disease except -
- A. Leptospirosis
- B. Rabies
- C. Scabies (Correct Answer)
- D. Brucellosis
Explanation: ***Scabies*** - **Scabies** is a parasitic skin infestation caused by the **Sarcoptes scabiei mite**, which typically spreads from person to person through direct skin contact. - While animal scabies exists, human scabies is primarily a **human-to-human transmission** disease and is not generally considered a zoonosis in the context of common human infections. *Leptospirosis* - **Leptospirosis** is a bacterial disease transmitted through contact with urine from infected animals or contaminated water/soil. - It is a classic example of a **zoonotic disease** affecting a wide range of mammals, including rodents, livestock, and pets. *Rabies* - **Rabies** is a viral disease primarily transmitted to humans through the bite of an infected animal, usually a mammal. - It is a well-known and fatal **zoonotic disease** worldwide, with dogs being the most common source of human infection in many regions. *Brucellosis* - **Brucellosis** is a bacterial infection transmitted to humans through contact with infected animals (e.g., cattle, goats, sheep) or consumption of contaminated unpasteurized dairy products. - It is a prominent **zoonotic disease** resulting in fever, sweating, and weakness, among other symptoms.
Question 10: All following are at-risk group adults meriting Hepatitis B vaccination in low endemic areas except for which of the following?
- A. Medical/nursing personnel
- B. Patients with chronic liver disease
- C. Diabetics on insulin (Correct Answer)
- D. Patients on chronic hemodialysis
Explanation: ***Diabetics on insulin*** - This is the correct answer as the exception based on **guidelines at the time of this exam (2012)**. - At that time, diabetics were **not routinely listed** as a standard at-risk group for hepatitis B vaccination in low endemic areas, though the ACIP was beginning to recognize increased risk in this population. - **Current Update (Post-2012):** The **CDC/ACIP now recommends** hepatitis B vaccination for all previously unvaccinated adults with diabetes aged 19-59 years, due to documented increased risk of HBV infection associated with: - Shared blood glucose monitoring devices - Assisted blood glucose monitoring in healthcare settings - Outbreak investigations showing higher transmission rates - For the purpose of this historical exam question, diabetics were the exception among the listed groups. *Medical/nursing personnel* - Healthcare workers are at **high occupational risk** due to frequent exposure to blood and body fluids. - This has been a **standard, long-standing recommendation** for HBV vaccination regardless of endemic status. - The risk remains present even in low endemic areas due to potential exposure to infected patients. *Patients with chronic liver disease* - Individuals with pre-existing chronic liver disease are at risk of **severe outcomes** if they acquire hepatitis B infection. - Superimposed acute HBV infection can lead to: - Rapid progression to cirrhosis - Acute-on-chronic liver failure - Hepatocellular carcinoma - Vaccination is **crucial for prevention** and has been a standard recommendation. *Patients on chronic hemodialysis* - Hemodialysis patients face **elevated risk** of HBV acquisition due to: - Frequent vascular access procedures - Prolonged time in healthcare settings - Potential for nosocomial transmission in dialysis units - Their **immunocompromised state** increases risk of chronic infection and complications. - Vaccination is a **standard preventive measure** in this population.
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