Hospital Acquired Infections Practice Questions

Q: What is the most common infection in patients with prosthetic valves within one month of surgery?

Staphylococcus aureus. **Explanation:** Prosthetic Valve Endocarditis (PVE) is categorized based on the time elapsed since surgery, which dictates the likely causative organism. **1. Why Staphylococcus aureus is correct:** Infections occurring within **one year** of surgery are classified as **Early PVE**. Within the first month (and up to 12 months), the most common pathogens are **Staphylococci**. While *Staphylococcus epidermidis* (Coagulase-negative Staph) is historically the most frequent cause of early PVE overall, **Staphylococcus aureus** is the most common and aggressive cause of acute, early-onset infection (especially within the first 30 days), often introduced perioperatively via skin contamination or healthcare-associated bacteremia. **2. Why the other options are incorrect:** * **Streptococcus pneumoniae:** Rarely causes endocarditis; it is more commonly associated with community-acquired pneumonia or meningitis. * **Pseudomonas aeruginosa:** An uncommon cause of PVE, usually associated with IV drug use or specific contaminated hospital equipment. * **Enterococci:** These are the third most common cause of PVE but typically present as a subacute infection later in the postoperative course, often originating from the gastrointestinal or genitourinary tract. **High-Yield Clinical Pearls for NEET-PG:** * **Early PVE ( 1 year):** The microbial profile shifts to resemble native valve endocarditis, with **Viridans group Streptococci** being the most common. * **Culture-Negative Endocarditis:** Most commonly due to prior antibiotic therapy or fastidious organisms like the **HACEK** group or *Coxiella burnetii*. * **Duke’s Criteria:** Always remember that two positive blood cultures for *S. aureus* is a major criterion for diagnosis.

Q: Which organism is primarily responsible for catheter-associated urinary tract infections?

All of the above. **Explanation:** Catheter-associated urinary tract infection (CAUTI) is the most common hospital-acquired infection (HAI) globally. While **Escherichia coli** remains the most frequent pathogen isolated in both community and hospital settings, the microbiology of CAUTIs is characteristically **polymicrobial** and involves a wider range of opportunistic organisms compared to uncomplicated UTIs. * **E. coli (Option B):** It is the leading cause of all UTIs. In the context of catheters, it utilizes fimbriae to adhere to the catheter surface and bladder epithelium. * **Pseudomonas aeruginosa (Option A):** This is a classic nosocomial pathogen. It is notorious for forming thick **biofilms** on the inner and outer surfaces of the catheter, making it highly resistant to both host immune responses and antibiotics. * **Proteus mirabilis (Option C):** This organism produces the enzyme **urease**, which hydrolyzes urea into ammonia. This increases urinary pH, leading to the formation of **struvite stones** (encrustation) that can block the catheter lumen. Since all three organisms are major contributors to the pathogenesis of CAUTIs in a clinical setting, **"All of the above"** is the most accurate choice. **High-Yield Clinical Pearls for NEET-PG:** * **Biofilm formation** is the key pathogenetic mechanism in CAUTIs. * **Most common source:** The patient’s own colonic flora (endogenous) or the hands of healthcare workers (exogenous). * **Duration of catheterization** is the most important risk factor for developing bacteriuria. * **Prevention:** The single most effective way to prevent CAUTI is to limit the use of catheters and remove them as soon as clinically possible. Always use a **closed drainage system**.

Q: What is the most common source of Staphylococcus aureus in a hospital setting?

Infective wounds. **Explanation:** **1. Why "Infective Wounds" is Correct:** *Staphylococcus aureus* is a ubiquitous human pathogen and a leading cause of Hospital-Acquired Infections (HAIs). In a clinical setting, **infected wounds and abscesses** serve as the primary reservoir. These sites contain high bacterial loads that are easily shed into the environment. The organism is primarily transmitted via the **hands of healthcare workers** who come into contact with these infected sites or colonized skin (nasal carriage is also a major source in staff/patients). **2. Analysis of Incorrect Options:** * **A. Intravenous fluids:** While contaminated fluids can cause outbreaks, they are more commonly associated with Gram-negative bacteria (like *Klebsiella* or *Enterobacter*) or *S. epidermidis* if the hub is contaminated. *S. aureus* is more likely to enter via the insertion site skin rather than the fluid itself. * **C. Contaminated instruments:** These are more typically associated with organisms like *Pseudomonas* or *Acinetobacter* (if wet) or *Clostridium* spores (if improperly sterilized). While possible, it is not the *most common* source. * **D. Bed linen:** Linen can act as a fomite, but it is a secondary source. The bacteria reach the linen from the primary source—the patient’s infected wound or skin. **3. High-Yield Clinical Pearls for NEET-PG:** * **Most common site of colonization:** Anterior nares (30% of the healthy population are carriers). * **Most common cause of Post-operative Wound Infection:** *Staphylococcus aureus*. * **Handwashing:** The single most effective measure to prevent the spread of MRSA/Staphylococcal infections in hospitals. * **Screening:** Healthcare workers are often screened for nasal carriage during hospital outbreaks.

Q: What is the most common infection in patients with prosthetic valves?

Staphylococcus. **Explanation:** Prosthetic Valve Endocarditis (PVE) is a serious complication of valve replacement surgery. The etiology is primarily determined by the time elapsed since the surgery: 1. **Early PVE ( 1 year post-surgery):** The microbiology shifts to resemble community-acquired endocarditis, where *Streptococcus viridans* becomes more common, though Staphylococci remain significant. **Analysis of Options:** * **Staphylococcus (Correct):** *S. epidermidis* is the overall leading cause of early PVE due to its affinity for foreign bodies (prosthetics). *S. aureus* is also a frequent and more virulent cause. * **Pneumococcus (Incorrect):** *Streptococcus pneumoniae* is a rare cause of endocarditis; it typically causes pneumonia or meningitis. * **Pseudomonas (Incorrect):** While *Pseudomonas aeruginosa* can cause healthcare-associated infections, it is an uncommon cause of PVE, usually seen in IV drug users or specific nosocomial outbreaks. * **Enterococci (Incorrect):** These are the third most common cause of PVE (after Staph and Strep), often associated with genitourinary or gastrointestinal procedures, but they do not surpass Staphylococci in frequency. **High-Yield Clinical Pearls for NEET-PG:** * **Most common organism in Early PVE:** *Staphylococcus epidermidis* (CoNS). * **Most common organism in Late PVE:** *Viridans group Streptococci*. * **Most common organism in IV Drug Users:** *Staphylococcus aureus* (often affecting the Tricuspid valve). * **Culture-negative Endocarditis:** Most commonly due to prior antibiotic use or HACEK group organisms.

Q: Which one of the following is true about catheter-associated urinary tract infections?

Most catheter-associated UTI patients are symptomatic. **Explanation:** **Catheter-Associated Urinary Tract Infection (CAUTI)** is the most common healthcare-associated infection worldwide. 1. **Why Option A is Correct:** While many textbooks historically emphasized asymptomatic bacteriuria, clinical guidelines (IDSA) and NEET-PG patterns highlight that in a clinical setting, a diagnosis of CAUTI specifically requires the presence of **symptoms** (e.g., fever, suprapubic tenderness, costovertebral angle pain) along with significant bacteriuria. Most patients who meet the formal criteria for "infection" (rather than just colonization) are symptomatic. 2. **Why Other Options are Incorrect:** * **Option B:** Significant bacteriuria is not delayed until 2 weeks. In fact, the risk of bacteriuria increases by **3–10% per day** of catheterization. By the end of **one week**, nearly 25% of patients develop bacteriuria, and almost 100% do so by 30 days. * **Option C:** The most common causative organisms are **Gram-negative bacilli**, specifically ***Escherichia coli*** (most common), followed by *Klebsiella*, *Proteus*, and *Pseudomonas*. *Staphylococcus* and *Streptococcus* are less frequent causes compared to enteric bacilli. **High-Yield Clinical Pearls for NEET-PG:** * **Definition:** CAUTI is defined as a UTI occurring in a patient who has an indwelling urinary catheter in place for >2 days or within 48 hours of removal. * **Most Important Risk Factor:** The **duration of catheterization** is the single most important modifiable risk factor. * **Biofilm Formation:** Bacteria (especially *Proteus mirabilis*) form biofilms on the catheter surface, protecting them from antibiotics and the host immune system. * **Prevention:** The most effective prevention strategy is avoiding unnecessary catheterization and using a **closed drainage system**. Routine bladder irrigation or systemic antibiotics are NOT recommended for prevention.

Q: A patient in the postoperative ICU with an intravenous catheter developed spikes of fever. What is the most likely causative organism?

Coagulase-negative staphylococci. **Explanation:** The clinical scenario describes a **Catheter-Related Bloodstream Infection (CRBSI)**, a common hospital-acquired infection (HAI) in ICU settings. **Why Coagulase-negative staphylococci (CoNS) is correct:** CoNS, specifically ***Staphylococcus epidermidis***, is the most common cause of infections associated with indwelling medical devices (intravenous catheters, prosthetic valves, shunts). These organisms are normal skin flora that gain entry during catheter insertion or manipulation. Their primary virulence factor is the ability to produce a **biofilm (slime layer)**, which allows them to adhere to plastic surfaces and protects them from both the host immune system and antibiotics. **Analysis of Incorrect Options:** * **A. E. coli:** While a leading cause of HAIs, it is most commonly associated with **Urinary Tract Infections (UTIs)** secondary to catheterization, not primary IV line infections. * **C. Pseudomonas:** A common cause of **Ventilator-Associated Pneumonia (VAP)** and burn wound infections in the ICU, but less frequent than CoNS for routine IV catheter-related spikes of fever. * **D. Streptococcus agalactiae (GBS):** Primarily associated with neonatal sepsis and meningitis; it is not a common cause of catheter-related HAIs in adults. **NEET-PG High-Yield Pearls:** * **Most common organism in CRBSI:** CoNS (Staph. epidermidis). * **Most common organism in Surgical Site Infections (SSI):** *Staphylococcus aureus*. * **Most common organism in Catheter-Associated UTI (CAUTI):** *E. coli*. * **Diagnosis of CRBSI:** Established when the same organism grows from both a percutaneous blood culture and the catheter tip (using **Maki’s semi-quantitative technique** showing >15 CFU).

Question 1

A patient with a post-cholecystectomy biliary stricture underwent ERCP three days ago and subsequently developed acute cholangitis. What is the most likely causative organism?

Accepted Answer

Escherichia coli

Answer

Bacillus fragilis

Answer

Streptococcus viridans

Answer

Pseudomonas aeruginosa

Question 2

What is the most common infection in patients with prosthetic valves within one month of surgery?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pneumoniae

Answer

Pseudomonas aeruginosa

Answer

Enterococci

Question 3

Universal (standard) precautions to be observed by surgeons for the prevention of hospital-acquired HIV infection include the following except:

Accepted Answer

Pre-operative screening of all patients for HIV

Answer

Wearing gloves and other barrier precautions

Answer

Washing hands on contamination

Answer

Handling sharp instruments with care

Question 4

Which organism is primarily responsible for catheter-associated urinary tract infections?

Accepted Answer

All of the above

Answer

Pseudomonas

Answer

E. coli

Answer

Proteus

Question 5

What is the most common source of Staphylococcus aureus in a hospital setting?

Accepted Answer

Infective wounds

Answer

Intravenous fluids

Answer

Contaminated instruments

Answer

Bed linen

Question 6

In an ICU patient on invasive monitoring, which of the following is NOT a cause of bacterial sepsis?

Accepted Answer

Humidified air

Answer

Orotracheal intubation

Answer

Intra-arterial line

Answer

Central venous catheter

Question 7

What is the most common infection in patients with prosthetic valves?

Accepted Answer

Staphylococcus

Answer

Pneumococcus

Answer

Pseudomonas

Answer

Enterococci

Question 8

Which one of the following is true about catheter-associated urinary tract infections?

Accepted Answer

Most catheter-associated UTI patients are symptomatic

Answer

Significant bacteriuria occurs in patients catheterized longer than 2 weeks

Answer

The most common causative organisms are Staphylococcus and Streptococcus

Answer

All of the above

Question 9

A patient in the postoperative ICU with an intravenous catheter developed spikes of fever. What is the most likely causative organism?

Accepted Answer

Coagulase-negative staphylococci

Answer

E. Coli

Answer

Pseudomonas

Answer

Streptococcus agalactiae

Question 10

What is the most cost-effective method of infection control?

Accepted Answer

Hand washing

Answer

Repeated disinfectant use

Answer

Alcohol-based hand rub

Answer

Prophylactic antibiotic therapy

Hospital Acquired Infections — MCQs

Hospital Acquired Infections — MCQs

On this page

Practice by Chapter

Want unlimited practice?