Hospital Acquired Infections — MCQs

An otherwise healthy patient who has just received a prosthetic aortic valve develops postoperative fever. Blood cultures are done and she is placed on broad-spectrum antibiotics. Two days later she is still febrile and clinically deteriorating. Which of the following organisms is the most probable etiologic agent?

Q46

Patient presenting with abdominal pain, diarrhea taking clindamycin for 5 days. Treated with metronidazole symptoms subsided. What is the causative agent -

Q47

Not a cause of community acquired pneumonia -

Q48

A 80-year-old male presented with acute shortness of breath. His SpO2 levels were 80%. He was immediately intubated and shifted to the ICU and put on the ventilator. He was a chronic smoker and a known case of COPD for the past 5 years. He was started on empirical antibiotics. Initial culture tests were negative. After 9 days, he developed certain lesions in the lungs along with high grade fever. A bronchoalveolar lavage was done and sent for Gram staining. The organism isolated was a multi-drug resistant organism. Biochemical reactions revealed oxidase positive and did not ferment any sugars. The organism isolated is resistant to all antibiotics except: -

Q49

A study of nosocomial infections involving urinary catheters is performed. The study shows that the longer an indwelling urinary catheter remains, the higher the rate of symptomatic urinary tract infections (UTIs). Most of these infections are bacterial. Which of the following properties of these bacteria increase the risk for nosocomial UTIs?

Q50

Hospital-acquired organisms include all except?

Hospital Acquired Infections Indian Medical PG Practice Questions and MCQs

Question 41: What is the most effective method for preventing nosocomial infections?

A. Wearing a mask
B. Hand washing (Correct Answer)
C. Maintaining physical distance
D. Frequent bathing

Explanation: **Explanation:** **Hand washing** is universally recognized as the single most effective, simplest, and most cost-efficient method for preventing **Nosocomial Infections (Hospital-Acquired Infections - HAIs)**. The primary mechanism of pathogen transmission in healthcare settings is via the contaminated hands of healthcare workers. Hand hygiene disrupts the chain of infection by removing transient flora acquired during patient contact, thereby preventing cross-contamination between patients. **Analysis of Options:** * **A. Wearing a mask:** While essential for preventing droplet and airborne infections (e.g., Tuberculosis, Influenza), masks do not prevent the transmission of the most common HAIs, such as MRSA or VRE, which are primarily spread through contact. * **C. Maintaining physical distance:** Although useful in community settings for respiratory outbreaks (like COVID-19), it is impractical in a clinical setting where physical examination and bedside care are necessary. * **D. Frequent bathing:** While important for personal hygiene, it does not address the immediate transfer of pathogens between patients and staff during clinical procedures. **High-Yield Clinical Pearls for NEET-PG:** * **WHO’s "5 Moments for Hand Hygiene":** 1) Before touching a patient, 2) Before a clean/aseptic procedure, 3) After body fluid exposure risk, 4) After touching a patient, 5) After touching patient surroundings. * **Alcohol-based hand rubs (ABHR):** These are preferred for routine decontamination unless hands are visibly soiled or when dealing with spore-forming organisms like *Clostridium difficile* (where soap and water are mandatory). * **Duration:** Hand washing with soap and water should take **40–60 seconds**, while hand rubbing with alcohol should take **20–30 seconds**.

Question 42: What is the most common cause of urinary tract infections associated with Foley catheterization?

A. Escherichia coli (Correct Answer)
B. Klebsiella
C. Pseudomonas
D. Staphylococci

Explanation: **Explanation:** **1. Why Escherichia coli is correct:** *Escherichia coli* (E. coli) is the most common cause of both community-acquired and hospital-acquired (nosocomial) Urinary Tract Infections (UTIs). In the context of Foley catheterization, E. coli originates from the patient’s own colonic flora (endogenous infection). It possesses specific virulence factors, such as **P-pili (adhesins)**, which allow it to adhere to the uroepithelium and the surface of the catheter, leading to biofilm formation and subsequent infection. **2. Why other options are incorrect:** * **Klebsiella:** While a significant cause of healthcare-associated UTIs and known for multidrug resistance (ESBL producers), it ranks second to E. coli in frequency. * **Pseudomonas:** This is a common cause of **instrumentation-related** UTIs and is notorious for forming thick biofilms on catheters; however, it is less frequent than E. coli. It is often associated with chronic catheterization or prior antibiotic use. * **Staphylococci:** *S. saprophyticus* is a common cause of UTI in young, sexually active females (community-acquired), and *S. aureus* UTIs are usually secondary to bacteremia (hematogenous spread) rather than catheterization. **3. High-Yield Clinical Pearls for NEET-PG:** * **Most common overall cause of UTI:** *E. coli*. * **Most common cause of UTI in a patient with renal calculi:** *Proteus mirabilis* (urease-positive, leads to struvite stones). * **Biofilm formation:** This is the primary mechanism for Catheter-Associated UTI (CAUTI). The most common fungal cause is *Candida albicans*. * **Prevention:** The single most effective way to prevent CAUTI is to **avoid unnecessary catheterization** and remove the catheter as soon as possible. * **Diagnosis:** In catheterized patients, a colony count of **>10³ CFU/ml** is considered significant (compared to >10⁵ in non-catheterized patients).

Question 43: Which of the following organisms is most commonly associated with urinary tract infections in healthcare facilities?

A. Staphylococcus epidermidis
B. Staphylococcus aureus
C. Klebsiella (Correct Answer)
D. Streptococcus

Explanation: **Explanation:** **Catheter-Associated Urinary Tract Infections (CAUTI)** are the most common type of healthcare-associated infections (HAIs). The correct answer is **Klebsiella** because it belongs to the **Enterobacteriaceae** family, which are the predominant pathogens in hospital settings. While *E. coli* remains the overall most common cause of UTIs, *Klebsiella pneumoniae* is a major cause of multidrug-resistant (MDR) infections in hospitalized patients, particularly those with indwelling urinary catheters. **Analysis of Options:** * **Klebsiella (Correct):** It is a Gram-negative, encapsulated rod that frequently colonizes the gastrointestinal tract of hospitalized patients and spreads via the hands of healthcare workers. It is notorious for producing Extended-Spectrum Beta-Lactamases (ESBL) and Carbapenemases. * **Staphylococcus epidermidis:** This is a coagulase-negative staphylococcus (CoNS) and is the most common cause of **prosthetic valve endocarditis** and **catheter-related bloodstream infections (CRBSI)**, but not primary UTIs. * **Staphylococcus aureus:** While it can cause UTIs (often via hematogenous spread), it is more commonly associated with surgical site infections and pneumonia. * **Streptococcus:** Group B Streptococcus (S. agalactiae) can cause UTIs in pregnant women or the elderly, but it is not a leading cause of healthcare-associated UTIs compared to Gram-negative bacilli. **High-Yield Clinical Pearls for NEET-PG:** * **Most common HAI overall:** Urinary Tract Infection (UTI). * **Most common organism for CAUTI:** *E. coli*, followed by *Klebsiella* and *Proteus*. * **Biofilm formation:** This is the key pathogenic mechanism in CAUTI, where organisms like *Klebsiella* and *Pseudomonas* create a protective matrix on the catheter surface. * **Urease-positive organisms:** *Proteus* and *Klebsiella* can increase urinary pH, leading to the formation of struvite (triple phosphate) stones.

Question 44: What is the most common causative organism of prosthetic heart valve endocarditis?

A. S. aureus
B. S. epidermidis (Correct Answer)
C. S. viridans
D. Enterococcus

Explanation: ***S. epidermidis*** - **S. epidermidis** is the most common single causative organism of prosthetic heart valve (PHV) endocarditis, especially in the **early post-operative period** (within 60 days to 1 year of surgery). - This organism is a **coagulase-negative Staphylococcus** known for its ability to produce a **glycocalyx (biofilm)**, which adheres strongly to foreign materials like prosthetic valves. *S. viridans* - Typically the leading cause of **subacute infectious endocarditis** on native, damaged valves, often following minor **dental procedures**. - While it can cause late PHV endocarditis, it is much less frequent than staphylococcal species, which dominate PHV infections. *S. aureus* - **S. aureus** is the most common cause of **acute native valve endocarditis** and frequently implicated in endocarditis in **IV drug users**. - It is a major cause of PHV endocarditis, especially **late-onset** (more than 1 year post-surgery), but overall, **S. epidermidis** is considered the most common pathogen when considering all PHV infections. *Enterococcus* - **Enterococcus species** (especially *E. faecalis*) account for approximately **5-10% of prosthetic valve endocarditis** cases, particularly in late-onset infections. - While significant, enterococci are far less common than staphylococcal species in PHV endocarditis.

Question 45: An otherwise healthy patient who has just received a prosthetic aortic valve develops postoperative fever. Blood cultures are done and she is placed on broad-spectrum antibiotics. Two days later she is still febrile and clinically deteriorating. Which of the following organisms is the most probable etiologic agent?

A. Nocardia asteroides
B. Actinomyces israelii
C. Histoplasma capsulatum
D. Candida albicans (Correct Answer)

Explanation: ***Candida albicans*** - *Candida albicans* is a common cause of **early prosthetic valve endocarditis**, especially in patients with prolonged hospitalization, broad-spectrum antibiotic use, or central venous catheters [1]. - The patient's clinical deterioration despite broad-spectrum antibacterial antibiotics suggests a **fungal etiology**, as bacteria are typically covered by such therapy [2]. *Nocardia asteroides* - *Nocardia asteroides* typically causes **pulmonary or cutaneous infections** in immunocompromised individuals, less commonly endocarditis. - It would usually respond to specific antibiotics like **trimethoprim-sulfamethoxazole**, and its presentation as prosthetic valve endocarditis is rare. *Actinomyces israelii* - *Actinomyces israelii* causes **actinomycosis**, characterized by chronic, slowly progressive infections with abscesses and draining sinuses, often following oral or abdominal trauma. - While it can cause endocarditis, it is less common in the context of acute prosthetic valve infection and would likely present with a more indolent course. *Histoplasma capsulatum* - *Histoplasma capsulatum* is a **dimorphic fungus** endemic to the Ohio and Mississippi River valleys, primarily causing pulmonary infections. - Disseminated histoplasmosis with endocarditis is rare and typically occurs in immunocompromised patients, not usually in an otherwise healthy individual post-surgery.

Question 46: Patient presenting with abdominal pain, diarrhea taking clindamycin for 5 days. Treated with metronidazole symptoms subsided. What is the causative agent -

A. Clostridium difficile (Correct Answer)
B. Clostridium welchii
C. Clostridium perfringens
D. Clostridium botulinum

Explanation: ***Clostridium difficile*** - **Clindamycin** is a common antibiotic associated with **Clostridium difficile** infection, which causes **antibiotic-associated diarrhea** and **colitis**. - The successful treatment with **metronidazole** further supports the diagnosis of *C. difficile* infection. *Clostridium welchii* (also known as *Clostridium perfringens*) - Primarily causes **gas gangrene** and **food poisoning**, with symptoms more acute and severe than described. - Not typically associated with antibiotic-induced diarrhea but rather **contaminated food** or **wound infections**. *Clostridium perfringens* - This bacterium is a common cause of **food poisoning** (type A) featuring **abdominal cramps** and **diarrhea**, and **gas gangrene** (type C) due to deep tissue infections. - While it can cause diarrhea, it's not the classic cause of **antibiotic-associated diarrhea** like *C. difficile*. *Clostridium botulinum* - Produces a **neurotoxin** that causes **flaccid paralysis**, not abdominal pain and diarrhea due to antibiotic use. - The infection is typically acquired through **improperly canned food** or **wound contamination**.

Question 47: Not a cause of community acquired pneumonia -

A. Streptococcus pneumoniae
B. Haemophilus influenzae
C. Acinetobacter baumannii (Correct Answer)
D. Mycoplasma pneumoniae

Explanation: ***Acinetobacter baumannii*** - **Acinetobacter baumannii** is typically associated with **healthcare-associated pneumonia (HAP)**, especially in ventilated patients or those with prolonged hospital stays. - It is known for its **multidrug resistance** and is rarely a cause of community-acquired pneumonia (CAP). *Streptococcus pneumoniae* - **Streptococcus pneumoniae** is the **most common bacterial cause** of community-acquired pneumonia in adults. - It often presents with classic symptoms such as a **single rigour**, productive cough, and is typically sensitive to common antibiotics. *Haemophilus influenzae* - **Haemophilus influenzae** is a significant cause of CAP, particularly in patients with **underlying lung diseases** like COPD or in smokers. - It can cause both severe and milder forms of pneumonia. *Mycoplasma pneumoniae* - **Mycoplasma pneumoniae** is a common cause of **atypical pneumonia**, often referred to as "walking pneumonia." - It typically presents with a **gradual onset** of symptoms, including a persistent dry cough, headache, and malaise.

Question 48: A 80-year-old male presented with acute shortness of breath. His SpO2 levels were 80%. He was immediately intubated and shifted to the ICU and put on the ventilator. He was a chronic smoker and a known case of COPD for the past 5 years. He was started on empirical antibiotics. Initial culture tests were negative. After 9 days, he developed certain lesions in the lungs along with high grade fever. A bronchoalveolar lavage was done and sent for Gram staining. The organism isolated was a multi-drug resistant organism. Biochemical reactions revealed oxidase positive and did not ferment any sugars. The organism isolated is resistant to all antibiotics except: -

A. Azithromycin
B. Amoxicillin
C. Amikacin
D. Colistin (Correct Answer)

Explanation: ***Colistin*** - The patient's history of **COPD**, intubation, ventilator support, and development of lung lesions with fever after 9 days despite broad-spectrum antibiotics, points towards a **ventilator-associated pneumonia (VAP)** caused by a highly resistant organism. - The description of the organism as **oxidase-positive**, **non-fermenting**, and **multi-drug resistant (MDR)** strongly suggests ***Pseudomonas aeruginosa*** or ***Acinetobacter baumannii*** - both common causes of VAP. - **Colistin** (polymyxin E) is a **last-line antibiotic** for infections by these MDR Gram-negative non-fermenters due to its unique mechanism of action (disrupting bacterial cell membrane), which remains effective when other antibiotics fail due to various resistance mechanisms. *Azithromycin* - **Azithromycin** is a macrolide antibiotic primarily used for respiratory tract infections, but it is **not effective** against **MDR Gram-negative non-fermenters** like *Pseudomonas* or *Acinetobacter*. - Its mechanism involves inhibiting bacterial protein synthesis (50S ribosomal subunit), which is insufficient to overcome the resistance mechanisms of these organisms. *Amoxicillin* - **Amoxicillin** is a penicillin-class antibiotic effective against some Gram-positive and Gram-negative bacteria but is highly susceptible to inactivation by **beta-lactamases**. - It would be **completely ineffective** against the multi-drug resistant, non-fermenting Gram-negative organisms like *Pseudomonas aeruginosa* or *Acinetobacter baumannii* typically seen in VAP, which produce various **resistance enzymes** including extended-spectrum beta-lactamases (ESBLs) and carbapenemases. *Amikacin* - **Amikacin** is an aminoglycoside antibiotic that can be effective against severe Gram-negative infections, including some *Pseudomonas* and *Acinetobacter* strains. - However, in cases of **multi-drug resistance**, many strains develop resistance to aminoglycosides through various mechanisms including **enzymatic modification** (acetyltransferases, phosphotransferases) and **reduced permeability**. The question specifically states the organism is resistant to all antibiotics except one, indicating resistance to amikacin as well.

Question 49: A study of nosocomial infections involving urinary catheters is performed. The study shows that the longer an indwelling urinary catheter remains, the higher the rate of symptomatic urinary tract infections (UTIs). Most of these infections are bacterial. Which of the following properties of these bacteria increase the risk for nosocomial UTIs?

A. Enzyme elaboration
B. Biofilm formation (Correct Answer)
C. Quorum sensing
D. Exotoxin release

Explanation: ***Biofilm formation*** - **Biofilms** are communities of bacteria encased in a self-produced extracellular polymeric substance, adhering to surfaces like indwelling catheters. - The formation of a biofilm protects bacteria from antibiotics and host immune responses, allowing them to persist and proliferate, significantly increasing the risk of **catheter-associated urinary tract infections (CAUTIs)** over time. *Enzyme elaboration* - While some bacterial enzymes (e.g., urease) can contribute to UTI pathogenesis by increasing urine pH and promoting stone formation, it is not the primary property increasing the *risk* of nosocomial UTIs related to catheter duration. - The elaboration of various enzymes is a general virulence factor but doesn't specifically explain the increased risk due to the *presence* of a foreign body like a catheter. *Quorum sensing* - **Quorum sensing** is a system of stimuli and response correlated to population density, allowing bacteria to coordinate gene expression in response to their population density. - While quorum sensing plays a role in regulating virulence factors and biofilm maturation, it is a mechanism *within* a biofilm or bacterial population rather than the direct property of bacteria that increases the basal risk of infection on a catheter. *Exotoxin release* - **Exotoxins** are proteins secreted by bacteria that can cause damage to host cells and tissues, leading to specific disease symptoms (e.g., tetanus toxin, botulinum toxin). - While some exotoxins can contribute to the severity of infections, they are not the primary reason for the increased incidence of UTIs specifically due to the presence of an indwelling catheter; the physical presence of the catheter primarily promotes bacterial adhesion and persistence via means such as biofilm formation.

Question 50: Hospital-acquired organisms include all except?

A. Acinetobacter
B. Staphylococcus
C. Streptococcus (Correct Answer)
D. Pseudomonas

Explanation: ***Streptococcus*** - Among the options listed, **streptococcal species are the least commonly emphasized** as typical **hospital-acquired pathogens** in standard microbiology teaching. - While *Streptococcus pneumoniae* can cause hospital-acquired pneumonia and *Enterococcus* species (formerly classified as streptococci) are important nosocomial pathogens, **most classic streptococcal infections** such as **streptococcal pharyngitis** and **impetigo** are predominantly **community-acquired**. - In contrast to the other three organisms listed, streptococci are not typically associated with **ventilator-associated pneumonia**, **ICU-related infections**, or **multidrug-resistant hospital outbreaks**. *Acinetobacter* - **_Acinetobacter baumannii_** is a notorious **nosocomial pathogen**, particularly in ICU settings, causing **ventilator-associated pneumonia**, **bloodstream infections**, and **wound infections**. - Often **multidrug-resistant (MDR)** or **extensively drug-resistant (XDR)**, making it a major concern in hospital outbreaks. *Staphylococcus* - **_Staphylococcus aureus_**, especially **methicillin-resistant *S. aureus* (MRSA)**, is one of the most important causes of **HAIs** including surgical site infections, bloodstream infections, and pneumonia. - **Coagulase-negative staphylococci (CoNS)** are leading causes of **catheter-related bloodstream infections** and prosthetic device infections. *Pseudomonas* - **_Pseudomonas aeruginosa_** is a classic **nosocomial pathogen**, particularly in immunocompromised patients and those on mechanical ventilation. - Causes **ventilator-associated pneumonia**, catheter-associated UTIs, burn wound infections, and exhibits **intrinsic resistance** to many antibiotics.

Practice by Chapter

Epidemiology of Hospital Infections

Practice Questions

Catheter-Associated Urinary Tract Infections

Practice Questions

Ventilator-Associated Pneumonia

Practice Questions

Surgical Site Infections

Practice Questions

Central Line-Associated Bloodstream Infections

Practice Questions

Clostridium difficile Infection

Practice Questions

Hospital Infection Control Programs

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Isolation Precautions

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Hand Hygiene

Practice Questions

Environmental Cleaning and Disinfection

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Surveillance of Hospital Infections

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Bundle Approach to Prevention

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