Hospital Acquired Infections — MCQs
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An outbreak of staphylococcal infection involving umbilical cords of seven newborn babies was reported in the nursery. Bacteriological survey reveals that two nurses have a large number of Staphylococcus aureus in the nasopharynx. What test should be performed to determine whether these nurses may have been responsible for the outbreak?
Most common cause of infection caused by intravascular catheter -
A patient admitted to an ICU is on a central venous line for the last one week. He is on ceftazidime and amikacin. After 7 days of antibiotics, he develops a spike of fever, and his blood culture is positive for gram-positive cocci in chains, which are catalase negative. Following this, vancomycin was started, but the culture remained positive for the same organism even after 2 weeks of therapy. The most likely organism causing the infection is:
Which infection commonly spreads to newborns through caregivers?
Which gram-negative organism is particularly notorious for causing late-onset VAP with multidrug resistance?
Bacteria most commonly involved in prosthetic valvular heart disease within 2 months of surgery is:
All the following are common nosocomial infections except:
Most common catheter-related bloodstream infection is due to:
Commonest cause of nosocomial infection is
The most common pathogens responsible for nosocomial pneumonia in ICU are
Hospital Acquired Infections Indian Medical PG Practice Questions and MCQs
Question 51: An outbreak of staphylococcal infection involving umbilical cords of seven newborn babies was reported in the nursery. Bacteriological survey reveals that two nurses have a large number of Staphylococcus aureus in the nasopharynx. What test should be performed to determine whether these nurses may have been responsible for the outbreak?
- A. Coagulase testing
- B. Nasopharyngeal culture on mannitol salt agar
- C. Bacteriophage typing (Correct Answer)
- D. Protein A typing
Explanation: ***Bacteriophage typing*** - **Bacteriophage typing** involves using specific **bacteriophages** to identify different strains within a bacterial species based on their susceptibility to lysis by these phages. - This method helps determine if the specific strain of **Staphylococcus aureus** found in the nurses' nasopharynx matches the strain causing the outbreak in the newborns' umbilical cords, thereby establishing an epidemiological link. - This is the **classical method** for *S. aureus* strain typing in outbreak investigations. Modern molecular methods like PFGE, MLST, and whole genome sequencing have largely replaced bacteriophage typing, but it remains a fundamental concept tested in medical examinations. *Coagulase testing* - **Coagulase testing** differentiates **Staphylococcus aureus** (coagulase-positive) from other coagulase-negative staphylococci. - While it identifies the species, it does not provide the **strain-level differentiation** needed to link a specific individual to an outbreak. *Nasopharyngeal culture on mannitol salt agar* - **Mannitol salt agar** is a selective and differential medium used to isolate and identify **Staphylococcus aureus** from mixed cultures due to its ability to ferment mannitol and tolerate high salt concentrations. - This test would confirm the presence of **Staphylococcus aureus** in the nasopharynx but would not provide the detailed **strain-specific information** required to trace the source of the outbreak. *Protein A typing* - **Protein A** is a common cell wall component of **Staphylococcus aureus** that binds to the Fc region of immunoglobulins. - While its presence is characteristic of **Staphylococcus aureus**, **Protein A typing** does not offer the necessary **strain-specific resolution** to epidemiologically link an individual carrier to a specific outbreak strain.
Question 52: Most common cause of infection caused by intravascular catheter -
- A. Pseudomonas
- B. E. coli
- C. Staph aureus
- D. Coagulase negative staphylococci (Correct Answer)
Explanation: ***Coagulase negative staphylococci*** - **Coagulase-negative staphylococci** (e.g., *Staphylococcus epidermidis*) are the most common cause of **catheter-related bloodstream infections (CRBSI)**. - They are normal skin flora that can colonize catheters and form **biofilms**, making them difficult to eradicate. *Pseudomonas* - **Pseudomonas aeruginosa** is a common cause of healthcare-associated infections, but it is less frequently responsible for primary bloodstream infections from intravascular catheters compared to staphylococci. - It is often associated with infections in **immunocompromised patients** or those with prolonged hospital stays. *E. coli* - **Escherichia coli** is a common cause of **urinary tract infections (UTIs)** and intra-abdominal infections, which can sometimes lead to bacteremia. - While it can cause bloodstream infections, it is not the most common causative agent for infections directly originating from intravascular catheters. *Staph aureus* - **Staphylococcus aureus** is a significant cause of CRBSI and can lead to more severe, invasive infections like **endocarditis** and **septic shock**. - Although it is a common pathogen in CRBSI, **coagulase-negative staphylococci** collectively cause a greater number of these infections due to their prevalence as skin commensals and biofilm-forming capabilities.
Question 53: A patient admitted to an ICU is on a central venous line for the last one week. He is on ceftazidime and amikacin. After 7 days of antibiotics, he develops a spike of fever, and his blood culture is positive for gram-positive cocci in chains, which are catalase negative. Following this, vancomycin was started, but the culture remained positive for the same organism even after 2 weeks of therapy. The most likely organism causing the infection is:
- A. Staphylococcus aureus
- B. Viridans streptococci
- C. Enterococcus faecalis (Correct Answer)
- D. Coagulase negative Staphylococcus
Explanation: ***Enterococcus faecalis*** - The organism is a **gram-positive cocci in chains** and is **catalase negative**, which is consistent with *Enterococcus*. - **Vancomycin resistance** in *Enterococcus* (VRE) is a significant clinical problem, explaining the persistent positive culture despite vancomycin therapy. *Staphylococcus aureus* - *Staphylococcus aureus* is a **catalase-positive** organism, which contradicts the patient's culture results. - While it can be vancomycin-resistant (VRSA), the initial catalase test rules it out. *Viridans streptococci* - *Viridans streptococci* are typically **susceptible to vancomycin**, making a persistent positive culture after 2 weeks of therapy unlikely unless there's a serious underlying issue like endocarditis with large vegetations or an undrained abscess. - They are also **catalase-negative**, but the vancomycin resistance points away from this option. *Coagulase negative Staphylococcus* - **Coagulase-negative Staphylococci** (e.g., *Staphylococcus epidermidis*) are **catalase-positive**, which is inconsistent with the patient's culture results. - While they can cause central line infections and be vancomycin-resistant, the catalase test rules out this group.
Question 54: Which infection commonly spreads to newborns through caregivers?
- A. Candida parapsilosis (Correct Answer)
- B. Candida albicans
- C. Candida tropicalis
- D. Candida glabrata
Explanation: ***Candida parapsilosis*** - This species is a well-known cause of **nosocomial bloodstream infections** in neonates, particularly in **premature infants** and those with central venous catheters. It is often spread via the hands of **healthcare workers**. - Its ability to form **biofilms on medical devices** (like catheters) further facilitates its transmission and makes it a significant infectious agent in neonatal intensive care units (NICUs). *Candida albicans* - While *Candida albicans* is the **most common Candida species** causing infections in humans, including superficial and invasive candidiasis in neonates, its transmission is less frequently linked to direct caregiver spread in the context of outbreaks compared to *C. parapsilosis*. - Neonatal *C. albicans* infections are often acquired **vertically from the mother** or through endogenous gut colonization. *Candida tropicalis* - *Candida tropicalis* can cause **invasive candidiasis**, especially in immunocompromised patients, but it is less frequently implicated in **outbreaks** attributed to hand-to-patient transmission by caregivers in NICUs than *C. parapsilosis*. - It is often associated with **neutropenia** and broad-spectrum antibiotic use. *Candida glabrata* - *Candida glabrata* is a significant pathogen, particularly in adults and immunocompromised individuals, known for its **fluconazole resistance**. - While it can cause bloodstream infections, it is not typically recognized as a primary cause of **caregiver-spread outbreaks** in newborns to the same extent as *C. parapsilosis*.
Question 55: Which gram-negative organism is particularly notorious for causing late-onset VAP with multidrug resistance?
- A. Klebsiella
- B. Pseudomonas aeruginosa
- C. Acinetobacter (Correct Answer)
- D. Staphylococcus aureus
Explanation: ***Acinetobacter*** - *Acinetobacter baumannii* is particularly notorious for causing **late-onset VAP** (>5 days) with extensive **multidrug resistance**, including pan-drug resistant strains (resistant to carbapenems, polymyxins, and tigecycline). - Its ability to survive on surfaces for prolonged periods, form biofilms, and its intrinsic resistance mechanisms make it a significant challenge in ICU environments. - Often exhibits resistance to nearly all available antibiotics, earning it a place in the **ESKAPE pathogens** group. *Klebsiella* - While *Klebsiella pneumoniae* can cause VAP and exhibits multidrug resistance through **extended-spectrum beta-lactamase (ESBL)** and carbapenemase production, it is not as characteristically associated with late-onset VAP as *Acinetobacter* and *Pseudomonas*. - More commonly causes **healthcare-associated infections** including urinary tract infections and bloodstream infections. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is also a major cause of **late-onset VAP** with significant **multidrug resistance** potential, particularly in patients with prolonged mechanical ventilation and underlying lung disease. - Can exhibit carbapenem resistance and is part of the ESKAPE pathogens. - However, *Acinetobacter baumannii* is considered particularly "notorious" due to its more extensive pan-drug resistance patterns and extremely limited treatment options. *Staphylococcus aureus* - *Staphylococcus aureus* is a **Gram-positive** organism, not Gram-negative, making it incorrect based on the question's specification. - While **MRSA** is a common cause of both early and late-onset VAP, it does not meet the Gram-negative criterion.
Question 56: Bacteria most commonly involved in prosthetic valvular heart disease within 2 months of surgery is:
- A. Staphylococcus epidermidis (Correct Answer)
- B. Streptococcus viridans
- C. Enterococci
- D. Hemophilus
Explanation: ***Staphylococcus epidermidis*** - This coagulase-negative staphylococcus is a common cause of **early-onset prosthetic valve endocarditis (PVE)**, occurring within 2 months of surgery. - It is a normal skin flora, and infections are often related to **intraoperative contamination** during valve replacement surgery. *Streptococcus viridans* - This group of streptococci is a leading cause of **late-onset PVE** and **native valve endocarditis (NVE)**, often following dental procedures. - Infections typically occur more than 2 months post-surgery, differentiating it from early-onset cases. *Enterococci* - Enterococci can cause both **NVE** and **PVE**, but they are more commonly associated with infections in patients with **nosocomial acquisition** or those undergoing genitourinary or gastrointestinal procedures. - While they can occur post-surgery, they are not the most common causative agent within the first 2 months compared to *Staphylococcus epidermidis*. *Hemophilus* - *Haemophilus species* are considered part of the **HACEK group** (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella), which are known for causing **culture-negative endocarditis**. - While they can cause endocarditis, they are rare causes of early-onset PVE and are more associated with subacute or chronic forms of endocarditis.
Question 57: All the following are common nosocomial infections except:
- A. Staph. aureus
- B. Mycobacterium (Correct Answer)
- C. Enterobacteriaceae
- D. P. aeruginosa
Explanation: ***Mycobacterium*** - **Mycobacterium** species are not typically considered common causes of **acute nosocomial infections** because they are slow-growing and usually cause chronic infections. - While healthcare workers or patients can acquire tuberculosis in healthcare settings, it is less common for *Mycobacterium* to be the cause of rapidly developing, typical healthcare-associated infections like pneumonia or bloodstream infections. *Staph. aureus* - **_Staphylococcus aureus_** is a very common cause of **nosocomial infections**, particularly **MRSA (methicillin-resistant *S. aureus*)**, leading to surgical site infections, bloodstream infections, and pneumonia. - It colonizes healthcare workers and patients, making it easily transmissible in hospital environments. *Enterobacteriaceae* - **Enterobacteriaceae** (e.g., _E. coli_, _Klebsiella_, _Enterobacter_) are frequently implicated in **nosocomial infections**, especially **urinary tract infections (UTIs)**, pneumonia, and bloodstream infections. - These bacteria are part of the normal flora but can cause serious infections when introduced into sterile sites or in immunocompromised patients. *P. aeruginosa* - **_Pseudomonas aeruginosa_** is a significant cause of **nosocomial infections**, particularly in intensive care units (ICUs) and among immunocompromised patients. - It is known for causing **ventilator-associated pneumonia (VAP)**, UTIs, and wound infections, often exhibiting multidrug resistance.
Question 58: Most common catheter-related bloodstream infection is due to:
- A. Coagulase-negative Staphylococci (CoNS) (Correct Answer)
- B. Candida species
- C. Gram-negative bacilli
- D. Staphylococcus aureus (S. aureus)
Explanation: ***Coagulase-negative Staphylococci (CoNS)*** - **Coagulase-negative Staphylococci (CoNS)**, particularly *Staphylococcus epidermidis*, are the most common cause of **catheter-related bloodstream infections (CRBSIs)** due to their ability to form **biofilms** on catheter surfaces. - Their ubiquity on the skin, combined with their capacity for **adherence** and **biofilm production**, facilitates their entry and proliferation within the catheter lumen. *Candida species* - While *Candida species* (e.g., *Candida albicans*) are significant causes of CRBSIs, especially in **immunocompromised** patients or those on **broad-spectrum antibiotics**, they are less common overall than CoNS. - Risk factors for *Candida* CRBSIs include prolonged hospitalization, total parenteral nutrition, and **central venous catheters**. *Gram-negative bacilli* - **Gram-negative bacilli** (e.g., *Klebsiella pneumoniae*, *Escherichia coli*, *Pseudomonas aeruginosa*) are important pathogens in CRBSIs, often associated with **severe sepsis** and higher mortality rates. - However, their overall incidence in catheter-induced infections is lower than that of CoNS, though they are more prevalent in certain hospital units like **ICUs**. *Staphylococcus aureus (S. aureus)* - **Staphylococcus aureus** causes clinically significant CRBSIs, often leading to more severe infections, including **endocarditis** and **septic emboli**, than CoNS. - While *S. aureus* infections are serious, CoNS remain the most frequently isolated organism in all CRBSI cases, partly due to the high carriage rate of *S. epidermidis* on human skin.
Question 59: Commonest cause of nosocomial infection is
- A. Staphylococci (Correct Answer)
- B. Klebsiella
- C. Enterobacteriaceae
- D. Pseudomonas
Explanation: ***Staphylococci*** - **Staphylococci**, particularly *Staphylococcus aureus* (including MRSA) and coagulase-negative staphylococci, are the **most common cause** of nosocomial infections according to current surveillance data from CDC, WHO, and Indian hospital studies. - They are the leading cause of **surgical site infections**, **catheter-related bloodstream infections**, **ventilator-associated pneumonia**, and **skin and soft tissue infections** in hospital settings. - Their ability to form biofilms on medical devices, antibiotic resistance (especially MRSA), and widespread colonization of healthcare workers and patients make them the predominant nosocomial pathogen. *Enterobacteriaceae* - The family **Enterobacteriaceae** (including *E. coli*, *Klebsiella*, *Enterobacter*) represents a major group of gram-negative nosocomial pathogens. - They are very common causes of **urinary tract infections**, **pneumonia**, and **bloodstream infections**, particularly associated with indwelling catheters and ventilators. - While collectively representing a large proportion of nosocomial infections, they are the **second most common** group after Staphylococci in most contemporary studies. *Pseudomonas* - *Pseudomonas aeruginosa* is an important nosocomial pathogen, particularly in **ventilator-associated pneumonia**, **burn infections**, and infections in immunocompromised patients. - It accounts for approximately 10-15% of nosocomial infections and is especially problematic due to its intrinsic antibiotic resistance. *Klebsiella* - **Klebsiella** (particularly *K. pneumoniae*) is a member of the Enterobacteriaceae family and an important individual pathogen causing **pneumonia** and **urinary tract infections** in healthcare settings. - While a common pathogen, it represents only a subset of both the Enterobacteriaceae family and overall nosocomial infections, making it less common than the entire Staphylococci group.
Question 60: The most common pathogens responsible for nosocomial pneumonia in ICU are
- A. Mycoplasma
- B. Gram-negative bacteria (Correct Answer)
- C. Virus
- D. Gram-positive bacteria
Explanation: ***Gram-negative bacteria*** - **Gram-negative bacteria** such as *Pseudomonas aeruginosa*, *Klebsiella pneumoniae*, and *Escherichia coli* are frequently colonizers of the critically ill. - Patients in the ICU are at high risk for ventilator-associated pneumonia and healthcare-associated pneumonia, often due to **multi-drug resistant gram-negative bacteria**. *Mycoplasma* - **Mycoplasma pneumoniae** is a common cause of **community-acquired pneumonia**, particularly in younger adults. - It is **rarely a cause of nosocomial pneumonia** and is not typically associated with the severe illnesses seen in ICU settings. *Virus* - While viruses can cause pneumonia, especially in immunocompromised individuals, they are **less common as primary causative agents of nosocomial pneumonia** in ICU settings compared to bacterial pathogens. - Viral pneumonia like **influenza** or **RSV** are usually community-acquired but can lead to secondary bacterial infections. *Gram-positive bacteria* - **Gram-positive bacteria**, particularly **methicillin-resistant *Staphylococcus aureus* (MRSA)**, are important causes of nosocomial pneumonia and are increasingly prevalent. - However, **Gram-negative bacteria** are still **more frequently isolated** in general nosocomial and ventilator-associated pneumonia cases in the ICU setting.
Practice by Chapter
Epidemiology of Hospital Infections
Practice Questions
Catheter-Associated Urinary Tract Infections
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Ventilator-Associated Pneumonia
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Surgical Site Infections
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Central Line-Associated Bloodstream Infections
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Clostridium difficile Infection
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Hospital Infection Control Programs
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Isolation Precautions
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Hand Hygiene
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Environmental Cleaning and Disinfection
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Surveillance of Hospital Infections
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Bundle Approach to Prevention
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