Infectious Diseases — MCQs

Infectious Diseases Indian Medical PG Practice Questions and MCQs

Question 1271: Which of the following is a characteristic symptom of Bacillus cereus food poisoning?

A. Abdominal cramps
B. Vomiting (emetic type) (Correct Answer)
C. Fever (uncommon)
D. Diarrhea (diarrheal type)

Explanation: ***Vomiting (emetic type)*** - The **emetic type** of *Bacillus cereus* food poisoning is characterized by prominent **nausea and vomiting** with a rapid onset (within 1-5 hours) after consuming food, particularly rice [1],[2]. - This is caused by the preformed **cereulide toxin**, a heat-stable cyclic depsipeptide [2]. *Abdominal cramps* - While *Bacillus cereus* food poisoning can include abdominal cramps, they are a more general symptom and not as specifically characteristic or defining as the emetic or diarrheal presentations [1],[2]. - Abdominal cramps are often present in both the emetic and diarrheal forms, but the distinctive feature lies in the primary gastrointestinal manifestation [3]. *Fever (uncommon)* - Fever is **rarely a prominent symptom** in *Bacillus cereus* food poisoning, distinguishing it from many other bacterial foodborne illnesses. - The disease is primarily mediated by toxins, leading to localized GI symptoms rather than systemic inflammatory responses that cause fever. *Diarrhea (diarrheal type)* - *Bacillus cereus* also causes a **diarrheal type** of food poisoning, characterized by diarrhea and abdominal pain, but typically with a longer incubation period (6-15 hours) and is caused by different toxins (**hemolysin BL and non-hemolytic enterotoxin**) [2]. - While diarrhea is a characteristic symptom of *Bacillus cereus* diarrheal type, the question lists vomiting as the emetic type, focusing on the specific emetic presentation which is distinct [3].

Question 1272: Which of the following statements regarding giardiasis is false?

A. Metronidazole is the drug of choice
B. Absence of fever
C. Diarrhea with steatorrhea
D. Bloody diarrhea (Correct Answer)

Explanation: Bloody diarrhea - **Giardiasis** is caused by the flagellate **_Giardia lamblia_**, which colonizes the small intestine and disrupts nutrient absorption, leading to **non-bloody diarrhea** [1]. - The parasite does not invade the intestinal wall, so **bloody stools are not a typical feature**; their presence suggests other infectious agents or conditions [1]. *Diarrhea with steatorrhea* - **_Giardia lamblia_ infection** impairs fat absorption in the small intestine, leading to the characteristic **fatty, foul-smelling stools known as steatorrhea**. - This malabsorption is due to damage to the brush border of enterocytes and disruption of bile salt metabolism. *Metronidazole is the drug of choice* - **Metronidazole** is indeed the **first-line treatment** for giardiasis, highly effective against the parasitic trophozoites. - Other effective alternatives include **tinidazole** and **nitazoxanide**, depending on regional resistance patterns and patient factors. *Absence of fever* - **Giardiasis** typically causes **gastrointestinal symptoms** such as diarrhea, abdominal cramps, and bloating, without systemic signs like fever [1]. - The absence of fever helps differentiate giardiasis from invasive infections that cause inflammatory responses.

Question 1273: Which of the following statements regarding the management of a nurse who got an accidental prick from an HIV-infected needle is true? Select the correct option.

A. Post-exposure prophylaxis should be started within 72 hours of exposure.
B. Viral markers are checked at the time of the prick.
C. Lamivudine is used as monotherapy in post-exposure prophylaxis.
D. Follow-up HIV testing is performed only at 6 months post-exposure. (Correct Answer)

Explanation: ***Follow-up HIV testing is performed only at 6 months post-exposure.*** - While initial testing is done at baseline, **follow-up HIV testing** is performed at 6 weeks, 3 months, and 6 months to ensure complete seroconversion detection [1]. - The 6-month mark is crucial, as it typically captures the vast majority of seroconversions and is often the final follow-up given [1]. *Post-exposure prophylaxis should be started within 72 hours of exposure.* - **Post-exposure prophylaxis (PEP)** should ideally be initiated as soon as possible, preferably within **1-2 hours** of exposure. - While recommended within 72 hours, its efficacy significantly decreases with delayed administration, making earlier intervention critical. *Lamivudine is used as monotherapy in post-exposure prophylaxis.* - **PEP regimens** for HIV typically involve a **combination of three antiviral drugs** from at least two different classes, not monotherapy. - Using a single drug like lamivudine would be ineffective in preventing HIV seroconversion and could promote drug resistance. *Viral markers are checked at the time of the prick.* - At the time of the prick (baseline), **HIV status of the exposed individual** is checked, not the viral markers of the source patient [1]. - Knowing the source patient's viral load can influence the PEP regimen, but baseline testing on the exposed healthcare worker is primarily for their own HIV status [1].

Question 1274: Which of the following is the least common mode of transmission of HIV?

A. Homosexual contact
B. Heterosexual contact
C. Transfusion of blood products (Correct Answer)
D. Intravenous drug use

Explanation: ***Transfusion of blood products*** - In countries with robust screening, **blood product transfusions** have become an extremely rare source of HIV transmission due to meticulous testing of donated blood [2]. - While historically a significant route, advancements in blood screening and donor selection have nearly eliminated this risk, making it the **least common** mode in many regions [2]. *Homosexual contact* - **Unprotected anal intercourse** between men has been, and remains, a predominant mode of HIV transmission globally, particularly in developed countries [1]. - The risk is high due to the **fragility of rectal mucosa** and the potential for trauma during intercourse. *Heterosexual contact* - **Unprotected heterosexual intercourse** is the most common mode of HIV transmission globally, especially in sub-Saharan Africa [1]. - The risk is influenced by the presence of **other sexually transmitted infections** (STIs) and viral load of the infected partner. *Intravenous drug use* - **Sharing contaminated needles and syringes** among intravenous drug users is a highly efficient way to transmit HIV [1]. - This mode facilitates direct transfer of infected blood from one individual to another.

Question 1275: Which of the following is not considered an opportunistic infection in AIDS?

A. Candidiasis
B. Kaposi's sarcoma
C. Rubella (Correct Answer)
D. Cytomegalovirus infection

Explanation: ***Rubella*** - Rubella, or **German measles**, is a relatively mild viral infection that typically affects children and is not considered an **opportunistic infection** in immunocompromised individuals like those with AIDS [1]. - While it can cause congenital rubella syndrome in infants whose mothers are infected during pregnancy, it does not disproportionately affect or cause severe disease in AIDS patients due to their compromised immunity [1]. *Candidiasis* - **Oropharyngeal** and **esophageal candidiasis** are common opportunistic infections in AIDS patients, often indicating significant immune suppression [2,3]. - The fungus *Candida albicans* can proliferate unchecked when the **CD4 count** is low [2]. *Kaposi's sarcoma* - This is a **cancer** caused by the **human herpesvirus 8 (HHV-8)**, which is a classic AIDS-defining illness [3]. - Its presence indicates severe immunodeficiency and was a hallmark of the early AIDS epidemic [3]. *Cytomegalovirus infection* - **Cytomegalovirus (CMV)** can cause severe and widespread disease in AIDS patients, including **retinitis**, **colitis**, and **encephalitis** [2]. - It becomes a significant risk when the **CD4 count** drops below 100 cells/mm³ [2].

Question 1276: What is the cause of perihepatic fibrosis in Fitz-Hugh-Curtis syndrome?

A. Bile Duct Injury
B. Chronic Alcoholism
C. Viral Hepatitis
D. Pelvic Inflammatory Disease (Correct Answer)

Explanation: ***Pelvic Inflammatory Disease*** - Fitz-Hugh-Curtis syndrome is a complication of **Pelvic Inflammatory Disease (PID)**, where infection spreads from the pelvic organs to the liver capsule [1]. - The inflammation leads to **perihepatic fibrosis** and adhesions, often described as "violin string" adhesions [1]. *Bile Duct Injury* - **Bile duct injury** can cause inflammation and fibrosis of the liver, but it typically affects the intrahepatic or extrahepatic bile ducts directly, rather than the liver capsule. - This condition is often associated with surgical procedures or gallstones, and not directly linked to PID. *Chronic Alcoholism* - **Chronic alcoholism** is a well-known cause of liver fibrosis and cirrhosis, but it specifically damages hepatocytes and leads to diffuse scarring of the liver parenchyma. - It does not primarily cause localized perihepatic fibrosis in the manner seen in Fitz-Hugh-Curtis syndrome. *Viral Hepatitis* - **Viral hepatitis** (e.g., Hepatitis B or C) causes diffuse inflammation and fibrosis throughout the liver, leading to cirrhosis over time. - It does not typically result in the characteristic localized perihepatic adhesions of Fitz-Hugh-Curtis syndrome, which is an ascendant infection.

Question 1277: What is the therapy of choice for pseudomembranous enterocolitis?

A. Penicillin
B. Ampicillin
C. Erythromycin
D. Vancomycin (Correct Answer)

Explanation: ***Vancomycin*** - **Oral vancomycin** is indicated for pseudomembranous enterocolitis, particularly for severe or recurrent cases, as it achieves high luminal concentrations in the colon to target *C. difficile* [1]. - Vancomycin works by inhibiting **bacterial cell wall synthesis**, effectively eradicating the toxigenic *C. difficile* strains responsible for the condition [1]. *Penicillin* - **Penicillin** is ineffective against *C. difficile* because *C. difficile* is a Gram-positive anaerobic bacterium producing toxins, and penicillin does not have the appropriate spectrum of activity. - In fact, many cases of pseudomembranous enterocolitis are triggered by prior **antibiotic use**, including penicillins, which disrupt the normal gut flora [2]. *Ampicillin* - Similar to penicillin, **ampicillin** is a broad-spectrum penicillin derivative and is not considered a treatment for *C. difficile* infection [3]. - Ampicillin can commonly be one of the **antibiotics that precipitates** the development of pseudomembranous enterocolitis by altering the normal gut microbiota [2]. *Erythromycin* - **Erythromycin**, a macrolide antibiotic, is not effective against *C. difficile* and is not used in the treatment of pseudomembranous enterocolitis. - Like other broad-spectrum antibiotics, erythromycin can **disrupt the normal gut flora**, potentially contributing to the overgrowth of *C. difficile* [2].

Question 1278: A patient who has developed fever and oral lesions after a trip to Bangkok is diagnosed as:

A. Bacterial skin infection
B. Viral skin infection
C. Autoimmune blistering disorder
D. Enterovirus infection (HFMD) (Correct Answer)

Explanation: ***Enterovirus infection (HFMD)*** - **Hand, foot, and mouth disease (HFMD)**, commonly caused by **enteroviruses** such as Coxsackievirus A16 and enterovirus 71, presents with fever and characteristic oral lesions (enanthems) as well as skin eruptions on the hands and feet [1]. - The patient's recent travel to **Bangkok**, an endemic area for HFMD, further supports this diagnosis alongside the presentation of fever and oral lesions [2]. *Bacterial skin infection* - While bacteria can cause skin infections, they are less likely to manifest with typical **oral lesions** in conjunction with fever as the primary symptoms, unless it's a specific syndrome like Scarlet fever, which presents differently. - Bacterial infections often present with **pus**, **cellulitis**, or **abscess formation**, which are not indicated in the question's description [3]. *Viral skin infection* - Many viral infections can cause skin rashes, but the specific combination of **fever** and distinct **oral lesions** (enanthems) points more specifically towards enteroviral infections like HFMD, rather than a general viral skin infection [1]. - Other viral skin infections like **chickenpox** or **measles** have distinct patterns of rash and symptoms that differ from the described oral lesions [2]. *Autoimmune blistering disorder* - **Autoimmune blistering disorders** like pemphigus or bullous pemphigoid typically present with chronic **blister formation** and erosions, usually without acute onset fever or a recent travel history connection. - These conditions are not primarily infectious and do not typically resolve spontaneously within a short period like many viral infections.

Question 1279: In a patient where only Anti-HBsAg is positive in the serum, with all other viral markers being negative, this indicates

A. Acute hepatitis infection
B. Chronic hepatitis infection
C. Chronic carrier state
D. Immunized person with hepatitis B vaccine (Correct Answer)

Explanation: ***Immunized person with hepatitis B vaccine*** - The presence of **Anti-HBsAg** (Hepatitis B surface antibody) as the *only* positive marker indicates immunity to hepatitis B [1]. - This immunity is most commonly acquired through **vaccination**, which introduces HBsAg to the immune system, leading to anti-HBsAg production without actual infection [1]. *Acute hepatitis infection* - Acute hepatitis B infection would typically show positive **HBsAg** (Hepatitis B surface antigen) and **Anti-HBc IgM** (hepatitis B core antibody, IgM class) [1]. - Anti-HBsAg is generally *not* present during acute infection, as it signals resolution or immunity rather than active disease [1]. *Chronic hepatitis infection* - A chronic hepatitis B infection would involve persistent **HBsAg** positivity for more than six months, often accompanied by **Anti-HBc IgG** and sometimes **HBeAg** [1]. - The isolated presence of Anti-HBsAg rules out chronic infection [1]. *Chronic carrier state* - A chronic carrier state is characterized by persistent presence of **HBsAg** in the blood, indicating ongoing viral replication or presence [1]. - The absence of HBsAg and the sole presence of anti-HBsAg would contradict a chronic carrier state [1].

Question 1280: Which of the following is the MOST characteristic clinical feature of Giardiasis?

A. Diarrhea with foul-smelling stools (Correct Answer)
B. Presence of Giardia cysts in stool
C. Abdominal cramps and bloating
D. Nausea and vomiting

Explanation: ***Diarrhea with foul-smelling stools*** - This is a hallmark symptom of Giardiasis [1], resulting from **malabsorption of fats** due to parasite adherence to the intestinal lining. - The malabsorption leads to **steatorrhea**, characterized by greasy, malodorous, and often floating stools. *Presence of Giardia cysts in stool* - While essential for **diagnosis**, the presence of cysts in stool is a **laboratory finding**, not a clinical feature experienced by the patient. - Clinical features refer to the **symptoms and signs** a patient presents with [1], which are often what prompt diagnostic testing. *Abdominal cramps and bloating* - These are **common symptoms** of Giardiasis, but they are often present in various gastrointestinal disturbances and are **less specific** than foul-smelling diarrhea. - They also can be caused by gas production and intestinal irritation, which frequently accompany many forms of infectious diarrhea. *Nausea and vomiting* - Nausea and vomiting can occur in Giardiasis, but they are **less consistent** and characteristic than the distinctive diarrhea pattern. - These symptoms are **widespread in many gastrointestinal illnesses** and do not specifically point to Giardiasis more than other conditions.

Practice by Chapter

Principles of Antimicrobial Therapy

Practice Questions

Fever of Unknown Origin

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HIV/AIDS and Related Infections

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Tuberculosis and Mycobacterial Diseases

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Tropical and Parasitic Infections

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Viral Infections (Hepatitis, Herpes, etc.)

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Healthcare-Associated Infections

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Fungal Infections

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Sepsis and Septic Shock

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Infection in Immunocompromised Hosts

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Emerging and Re-emerging Infections

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Antimicrobial Resistance

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Vaccination Principles

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