Hospital Acquired Infections — MCQs

Hospital Acquired Infections Indian Medical PG Practice Questions and MCQs

Question 31: What is the most common pathogen causing ventilator-associated pneumonia?

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

Explanation: **Explanation:** Ventilator-associated pneumonia (VAP) is a subtype of hospital-acquired pneumonia (HAP) occurring more than 48–72 hours after endotracheal intubation. **Why Pseudomonas is correct:** *Pseudomonas aeruginosa* is the most frequently isolated pathogen in VAP, particularly in late-onset cases (occurring after 5 days of hospitalization). It is a Gram-negative, non-fermenting aerobe that thrives in the moist environments of respiratory equipment. Its ability to form biofilms on endotracheal tubes and its inherent resistance to many antibiotics make it a dominant and difficult-to-treat pathogen in the ICU setting. **Analysis of Incorrect Options:** * **Staphylococcus aureus (Option A):** While *S. aureus* (including MRSA) is a common cause of VAP, it generally ranks second to Gram-negative bacilli like *Pseudomonas*. It is more frequently associated with early-onset VAP or post-viral (e.g., influenza) pneumonia. * **Enterococci (Option C):** These are common causes of catheter-associated UTIs and surgical site infections but are rarely primary pathogens in pneumonia. * **Streptococcus (Option D):** *Streptococcus pneumoniae* is the leading cause of **Community-Acquired Pneumonia (CAP)**. While it can cause early-onset VAP, it is not the most common overall pathogen in the hospital setting. **High-Yield Clinical Pearls for NEET-PG:** * **Most common overall:** *Pseudomonas aeruginosa*. * **Most common Gram-positive:** *Staphylococcus aureus*. * **Early-onset VAP (<5 days):** Often caused by antibiotic-sensitive bacteria like *S. pneumoniae* or *H. influenzae*. * **Late-onset VAP (>5 days):** Predominantly MDROs (Multi-Drug Resistant Organisms) like *Pseudomonas*, *Acinetobacter baumannii*, and MRSA. * **Diagnosis:** Requires a new or progressive infiltrate on CXR plus clinical signs (fever, purulent secretions, or leukocytosis).

Question 32: Which of the following is NOT a diagnostic criterion for bloodstream infection from a central venous catheter?

A. Colony count from catheter culture is 5 times more than peripheral blood culture.
B. Blood culture from catheter shows colony formation at least 2 hours before the peripheral blood culture.
C. Quantitative catheter tip culture showing >10^3 CFU/catheter segment whereby the same organism is isolated from the catheter segment and a peripheral blood sample.
D. Apparent source of bloodstream infection present. (Correct Answer)

Explanation: ### Explanation **Core Concept:** A **Central Line-Associated Bloodstream Infection (CLABSI)** is defined as a primary laboratory-confirmed bloodstream infection (BSI) where an intravascular device was in place for >48 hours. The fundamental requirement for a diagnosis of CLABSI is that the bloodstream infection must **not** be secondary to an infection at another body site. **Why Option D is the Correct Answer:** If an **apparent source of infection** (e.g., pneumonia, UTI, or intra-abdominal abscess) is present and matches the organism found in the blood, the BSI is classified as secondary to that source, not a primary catheter-related infection. Therefore, the *absence* of another source is a prerequisite for diagnosing CLABSI. **Analysis of Incorrect Options (Diagnostic Criteria for CRBSI):** * **Option A:** A **Differential Quantitative Blood Culture** is positive for CRBSI if the colony count from the catheter-drawn blood is **≥3–5 times greater** than the peripheral blood sample. * **Option B:** **Differential Time to Positivity (DTP)** is a highly specific marker. If the culture from the central line turns positive **at least 2 hours (120 minutes) earlier** than the peripheral culture, it indicates a higher bacterial load in the catheter. * **Option C:** According to **Maki’s Semi-quantitative Method** (roll-plate technique), a growth of **>15 CFU** per catheter segment is significant. For **Quantitative sonication methods**, a threshold of **>10³ CFU** is used. If the same organism is isolated from both the tip and peripheral blood, it confirms the catheter as the source. **High-Yield Clinical Pearls for NEET-PG:** * **Most common organism:** Coagulase-negative Staphylococci (*S. epidermidis*). * **Most common site for infection:** Femoral vein (highest risk) > Internal Jugular > Subclavian (lowest risk). * **Prevention:** The "Central Line Bundle" includes hand hygiene, maximal sterile barrier precautions, and **Chlorhexidine skin antisepsis** (preferred over Povidone-iodine). * **Diagnosis:** Always collect paired blood samples (one from the catheter and one from a peripheral vein) before starting antibiotics.

Question 33: A known HIV-positive patient is admitted in an isolation ward after abdominal surgery following an accident. The resident doctor who changed his dressing the next day found it to be soaked in blood. Which of the following would be the right method of choice for discarding the dressing?

A. Pour 1% hypochlorite on the dressing material and send it for incineration in an appropriate bag.
B. Pour 5% hypochlorite on the dressing material and send it for incineration in an appropriate bag.
C. Put the dressing material directly in an appropriate bag and send for incineration. (Correct Answer)
D. Pour 2% Lysol on the dressing material and send it for incineration in an appropriate bag.

Explanation: ### Explanation **1. Why Option C is Correct:** According to the **Biomedical Waste (BMW) Management Rules (2016 and subsequent amendments)**, anatomical waste and soiled waste (items contaminated with blood, body fluids like dressings, plaster casts, etc.) must be disposed of in **Yellow Bags**. The standard treatment for yellow bag waste is **Incineration** or Plasma Pyrolysis. The core principle is that soiled waste should be placed directly into the designated bag without any prior chemical pretreatment. Pre-treating waste with chemicals like hypochlorite before incineration is not recommended because it can lead to the release of toxic gases (like dioxins and furans) during the combustion process. **2. Why Other Options are Incorrect:** * **Options A, B, and D:** These suggest pre-treating the dressing with disinfectants (Hypochlorite or Lysol) before incineration. Under current BMW guidelines, chemical pretreatment is generally reserved for liquid waste or laboratory waste (like cultures) before they are sent for final disposal. For solid soiled waste, adding liquid disinfectants increases the weight of the waste and interferes with the efficiency of the incinerator. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Yellow Bag:** Used for soiled waste, anatomical waste, expired medicines, and chemical waste. * **Red Bag:** Used for recyclable plastic waste (IV sets, catheters, gloves). These are treated by autoclaving/microwaving followed by shredding. * **White (Puncture-proof) Container:** Used for sharps (needles, scalpels). * **Blue Box:** Used for glass vials, ampoules, and metallic body implants. * **HIV Status:** The patient’s HIV status is a "distractor" in this question. BMW protocols are based on **Universal Precautions**, meaning all blood-soaked material is treated as potentially infectious regardless of the patient's known serology. * **Hypochlorite:** 1-2% is used for surface disinfection of blood spills, but not for soaking dressings intended for incineration.

Question 34: A person gets infected in a hospital and clinical manifestations appear after discharge. What is this type of infection called?

A. Nosocomial infection (Correct Answer)
B. Opportunistic infection
C. Epizootic infection
D. Physician induced

Explanation: ### Explanation **Correct Option: A. Nosocomial infection** A **Nosocomial infection** (also known as a Healthcare-Associated Infection or HAI) is defined as an infection acquired in a hospital or healthcare facility that was neither present nor incubating at the time of admission. The key diagnostic criteria for a nosocomial infection are: 1. Clinical manifestations appear **48 hours or more after admission**. 2. Clinical manifestations appear **within 30 days of discharge** (or up to 90 days/1 year for surgical site infections involving implants). Since the patient in the question developed symptoms after discharge but the acquisition occurred during the hospital stay, it is classified as a nosocomial infection. **Why other options are incorrect:** * **B. Opportunistic infection:** These are infections caused by organisms (often part of normal flora) that typically do not cause disease in healthy individuals but take advantage of a host with a compromised immune system (e.g., HIV/AIDS, chemotherapy). * **C. Epizootic infection:** This refers to an outbreak of an infectious disease in an animal population that spreads rapidly, analogous to an "epidemic" in humans. * **D. Physician induced:** Also known as **Iatrogenic infection**, this is a specific subset of nosocomial infections resulting directly from diagnostic or therapeutic procedures (e.g., infection following a catheterization or surgery). While related, "Nosocomial" is the broader, more appropriate term for hospital-acquired infections. --- ### NEET-PG High-Yield Pearls * **Most common Nosocomial Infection:** Urinary Tract Infection (UTI), usually associated with catheterization. * **Most common organism for Nosocomial UTI:** *Escherichia coli*. * **Most common organism for Nosocomial Pneumonia (VAP):** *Pseudomonas aeruginosa* or *Staphylococcus aureus*. * **Handwashing:** The single most effective way to prevent the spread of nosocomial infections. * **Incubation Period Rule:** If the signs appear within the first 48 hours of admission, it is generally considered a **Community-Acquired Infection**.

Question 35: If a parenteral needle stick injury occurs in a healthcare worker dealing with an AIDS patient, which of the following are necessary?

A. Serial serological testing of the source person
B. Serial serological testing of the healthcare worker
C. Zidovudine (AZT) prophylaxis to the healthcare worker (Correct Answer)
D. Wash the affected part with soap and water

Explanation: ### Explanation **Correct Option: C. Zidovudine (AZT) prophylaxis to the healthcare worker** The primary goal following a high-risk needle stick injury (NSI) from a known HIV-positive source is to prevent viral replication and systemic infection. **Post-Exposure Prophylaxis (PEP)** is the standard of care. Zidovudine (AZT) was the first drug proven to reduce the risk of HIV transmission after occupational exposure by approximately 81%. While modern PEP regimens now typically use a combination of three drugs (e.g., Tenofovir, Lamivudine, and Dolutegravir), Zidovudine remains the classic "textbook" answer for the most critical immediate intervention in this context. **Analysis of Incorrect Options:** * **Option A:** The source person is already known to have AIDS; further serial testing is redundant and does not protect the healthcare worker. * **Option B:** While the healthcare worker (HCW) undergoes baseline and follow-up testing (at 6 weeks, 12 weeks, and 6 months), this is a diagnostic protocol, not a preventive "necessity" that stops the infection like PEP does. * **Option D:** Washing with soap and water is the **first immediate step** (first aid), but it is not sufficient on its own to prevent transmission from a parenteral (deep) injury. In the hierarchy of "necessity" for preventing seroconversion, pharmacological prophylaxis (PEP) is the definitive medical requirement. **High-Yield Clinical Pearls for NEET-PG:** * **Risk of Transmission:** The average risk of HIV transmission after a percutaneous injury is **0.3%** (compared to 3% for HCV and 30% for HBV in non-immune individuals). * **Timing of PEP:** PEP should ideally be started within **2 hours** (the "golden hour") and definitely within 72 hours. * **Duration:** The standard duration for PEP is **28 days**. * **First Aid:** Do not squeeze the wound or use antiseptics like bleach; simply wash with soap and water.

Question 36: Nosocomial pneumonia is most commonly caused by which type of organism?

A. Gram-negative bacilli (Correct Answer)
B. Gram-positive bacilli
C. Gram-negative cocci
D. Mycoplasma

Explanation: **Explanation:** **1. Why Gram-negative bacilli (GNB) is correct:** Nosocomial pneumonia (Hospital-Acquired Pneumonia - HAP) occurs 48 hours or more after admission. The hospital environment and medical interventions (like endotracheal intubation) lead to the colonization of the oropharynx with multidrug-resistant (MDR) flora. **Gram-negative bacilli** are the predominant pathogens, accounting for approximately 50-70% of cases. The most common isolates include *Pseudomonas aeruginosa*, *Klebsiella pneumoniae*, *Escherichia coli*, and *Acinetobacter baumannii*. **2. Why other options are incorrect:** * **Gram-positive bacilli:** These (e.g., *Listeria*, *Bacillus anthracis*) are rare causes of pneumonia. While Gram-positive **cocci** (specifically MRSA) are the second most common cause of HAP, bacilli are not. * **Gram-negative cocci:** *Moraxella catarrhalis* and *Neisseria* are Gram-negative cocci; however, they are more frequently associated with community-acquired infections or COPD exacerbations rather than nosocomial pneumonia. * **Mycoplasma:** *Mycoplasma pneumoniae* is a classic cause of "Atypical Pneumonia" and is almost exclusively **Community-Acquired (CAP)**, typically affecting younger populations in crowded settings. **3. Clinical Pearls for NEET-PG:** * **Most common overall:** Gram-negative bacilli (specifically *Pseudomonas aeruginosa*). * **Most common Gram-positive:** *Staphylococcus aureus* (especially MRSA). * **VAP (Ventilator-Associated Pneumonia):** A subtype of HAP occurring >48 hours after endotracheal intubation; *Acinetobacter* and *Pseudomonas* are high-yield culprits here. * **Early-onset HAP (<5 days):** Often caused by antibiotic-sensitive bacteria (*S. pneumoniae*, *H. influenzae*). * **Late-onset HAP (>5 days):** Higher risk for MDR organisms like *Pseudomonas* and MRSA.

Question 37: What is the most common staphylococcal phage strain causing hospital infections?

A. 80/81 (Correct Answer)
B. 79/80
C. 3A/3C
D. 69/70

Explanation: **Explanation:** **1. Why Option A (80/81) is Correct:** Staphylococcus aureus strains are classified using **bacteriophage typing**, which identifies specific strains based on their susceptibility to lysis by different phages. Historically and clinically, **Phage Type 80/81** is the most notorious strain associated with hospital-acquired infections (nosocomial infections). It emerged in the 1950s as a highly virulent, multidrug-resistant strain (primarily resistant to Penicillin G) responsible for worldwide outbreaks of skin infections, sepsis, and pneumonia in nursery and surgical settings. **2. Analysis of Incorrect Options:** * **Option B (79/80):** While these are valid phage numbers, they do not represent the classic epidemic strain recognized in medical literature as the primary driver of historical hospital outbreaks. * **Option C (3A/3C):** These phages belong to **Phage Group II**. Group II strains (specifically types 3A, 3B, 3C, 55, and 71) are classically associated with **Staphylococcal Scalded Skin Syndrome (SSSS)** and bullous impetigo, rather than general hospital-acquired outbreaks. * **Option D (69/70):** These belong to **Phage Group III**, which often includes strains associated with gastrointestinal issues (food poisoning), but they are not the "most common" epidemic strain compared to 80/81. **3. NEET-PG High-Yield Pearls:** * **Phage Typing:** It is used for **epidemiological markers** to trace the source of an outbreak. It is performed only on *S. aureus* (coagulase-positive), not CoNS. * **Groups:** Phages are categorized into Groups I, II, III, and IV. Most hospital-acquired *S. aureus* strains belong to **Group I (including 80/81)** or **Group III**. * **MRSA:** Modern hospital-acquired MRSA strains are often non-typable or belong to specific clonal complexes (like CC5 or CC22), but for exam purposes, **80/81** remains the classic answer for the most common epidemic phage strain.

Question 38: There has been an outbreak of infections caused by methicillin-resistant Staphylococcus aureus in the surgical intensive care unit. What is the most effective means of limiting its spread?

A. Treatment with cephalosporins, to which most strains are sensitive
B. Treatment with nafcillin and gentamicin, which have a synergistic effect
C. Use of high-dose nafcillin alone and isolation
D. Treatment with glycopeptide (Correct Answer)

Explanation: ### Explanation **1. Why the correct answer is right:** Methicillin-resistant *Staphylococcus aureus* (MRSA) is defined by its resistance to almost all beta-lactam antibiotics (penicillins, cephalosporins, carbapenems) due to the acquisition of the **mecA gene**. This gene encodes an altered penicillin-binding protein (**PBP2a**) that has a low affinity for beta-lactams. Consequently, **Glycopeptides** (such as **Vancomycin** or Teicoplanin) are the drugs of choice for treating serious MRSA infections and limiting their spread in a clinical outbreak setting by achieving microbiological clearance. **2. Why the incorrect options are wrong:** * **Option A:** MRSA is inherently resistant to almost all **cephalosporins** (except 5th generation agents like Ceftaroline). Using them would be clinically ineffective. * **Option B & C:** **Nafcillin** is a penicillinase-resistant penicillin. By definition, MRSA is resistant to nafcillin. Adding gentamicin does not overcome the fundamental resistance of the PBP2a receptor. High-dose monotherapy with nafcillin will fail because the target site itself is altered. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Gold Standard for MRSA Detection:** The **Cefoxitin disk diffusion test** is preferred over oxacillin for detecting methicillin resistance in the lab. * **Mechanism of Resistance:** Alteration of target site (PBP2a) via the *mecA* gene. * **Infection Control:** While glycopeptides treat the infection, the **most effective non-pharmacological measure** to prevent the *spread* of MRSA in a ICU is strict **hand hygiene** and contact precautions. * **Alternative for MRSA:** For patients intolerant to Vancomycin or for VRSA, **Linezolid** (an oxazolidinone) or **Daptomycin** (a lipopeptide) are used. Note: Daptomycin cannot be used for MRSA pneumonia as it is inactivated by pulmonary surfactant.

Question 39: In a burn ward, multiple patients have developed Staphylococcus infections. Where is Staphylococcus typically colonized in the human body?

A. Throat
B. Nose (Correct Answer)
C. Vagina
D. Perianal region

Explanation: **Explanation:** The primary reservoir for *Staphylococcus aureus* in humans is the **anterior nares (nose)**. Approximately 20–30% of the general population are persistent nasal carriers, while about 60% are intermittent carriers. In a clinical setting like a burn ward, healthcare workers or patients who are nasal carriers can easily transfer the bacteria via hands to vulnerable sites (burn wounds), leading to healthcare-associated infections (HAIs). **Analysis of Options:** * **B. Nose (Correct):** The moist squamous epithelium of the anterior nares is the most frequent and consistent site of colonization. Nasal carriage is a major risk factor for surgical site infections and outbreaks in specialized units. * **A. Throat:** While *S. aureus* can be found in the oropharynx, it is a much less common site of colonization compared to the nose. The throat is more typically associated with *Streptococcus pyogenes*. * **C. Vagina:** *S. aureus* can colonize the vagina in a small percentage of women (relevant to Toxic Shock Syndrome), but it is not the primary or typical reservoir for the species. * **D. Perianal region:** This is a secondary site of colonization. While it can be a reservoir in persistent carriers, the nose remains the primary niche. **Clinical Pearls for NEET-PG:** * **Mupirocin:** This is the topical antibiotic of choice used for the **decolonization** of MRSA from the anterior nares of healthcare workers and patients. * **Hand Hygiene:** The most effective way to prevent the spread of *Staphylococcus* from colonized sites to patients is strict handwashing. * **Burn Wards:** *S. aureus* and *Pseudomonas aeruginosa* are the two most common isolates from burn wound infections.

Question 40: What is the most common cause of shunt infection following a Ventriculo-Peritoneal shunt?

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

Explanation: **Explanation:** The correct answer is **Staphylococcus epidermidis**. **1. Why Staphylococcus epidermidis is correct:** Ventriculo-Peritoneal (VP) shunt infections are primarily caused by organisms introduced during the perioperative period. *Staphylococcus epidermidis*, a Coagulase-Negative Staphylococcus (CoNS), is the most common commensal of the human skin. Its primary virulence factor is the ability to produce a **polysaccharide biofilm (slime layer)**, which allows it to adhere strongly to prosthetic materials like silicone catheters. This biofilm protects the bacteria from both the host immune system and systemic antibiotics, making it the leading cause of infections involving indwelling medical devices (shunts, prosthetic valves, and catheters). **2. Why the other options are incorrect:** * **Staphylococcus aureus:** While it is the second most common cause and often leads to more acute, fulminant infections, it is less frequent than *S. epidermidis*. * **Streptococcus viridans:** These are normal flora of the oropharynx and are typically associated with Subacute Bacterial Endocarditis (SBE) following dental procedures, not shunt infections. * **Streptococcus pneumoniae:** This is a common cause of community-acquired meningitis but is rarely implicated in healthcare-associated device infections. **3. NEET-PG High-Yield Pearls:** * **Most common overall cause of prosthetic device infections:** *Staphylococcus epidermidis*. * **Most common route of infection:** Intraoperative contamination by skin flora. * **Clinical Presentation:** Often presents with low-grade fever, shunt malfunction, or signs of increased intracranial pressure rather than classic meningeal signs. * **Management:** Usually requires both systemic antibiotics (e.g., Vancomycin) and surgical removal/replacement of the infected shunt.

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

Practice Questions

Isolation Precautions

Practice Questions

Hand Hygiene

Practice Questions

Environmental Cleaning and Disinfection

Practice Questions

Surveillance of Hospital Infections

Practice Questions

Bundle Approach to Prevention

Practice Questions

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