Surgical Site Infections — MCQs
What is the optimal timing for administering antibiotic prophylaxis before surgery?
Which of the following disorders would be more likely associated with Staphylococcus saprophyticus rather than Staphylococcus aureus?
Which of the following is the drug of choice for preoperative antibiotic prophylaxis in a patient undergoing cardiac surgery?
What is the term for bacteria that are actively dividing and have invaded the wound surface in the context of surgical site infection?
When do we have to start antibiotics to prevent post-operative infection?
What is the most common cause of postoperative fever within 24 hours?
Most common cause of infection caused by intravascular catheter -
Preferred time for prophylactic antibiotic administration for surgery?
Percentage of surgical site infection in patients with a clean-contaminated wound after prophylactic antibiotic administration?
Which of the following is true about tenosynovitis of the finger?
Surgical Site Infections Indian Medical PG Practice Questions and MCQs
Question 1: What is the optimal timing for administering antibiotic prophylaxis before surgery?
- A. Immediately before induction of anesthesia
- B. 30-60 minutes before incision (Correct Answer)
- C. 2-3 hours before surgery
- D. Immediately after surgery
Explanation: ***30-60 minutes before incision*** - This is the **optimal timing** recommended by WHO, CDC, and major surgical guidelines for most commonly used prophylactic antibiotics (cefazolin, cefuroxime). - Ensures **peak tissue and serum concentrations** are achieved at the time of incision, providing maximum protection against surgical site infections. - Based on **pharmacokinetic principles**: the antibiotic must be present at bactericidal concentrations in tissues when bacterial contamination occurs. - Studies show this timing significantly reduces surgical site infection rates compared to other timings. *Immediately before induction of anesthesia* - While acceptable in some protocols, this may be too early if there is a delay between induction and incision. - Could result in **declining antibiotic levels** by the time the incision is made, especially for antibiotics with shorter half-lives. *2-3 hours before surgery* - This is **too early** for most antibiotics. - Tissue levels may have already **declined below therapeutic concentrations** by the time of incision. - Does not provide adequate protection during the critical period of bacterial contamination. *Immediately after surgery* - This is **treatment, not prophylaxis**. - Offers **no preventive benefit** against intraoperative contamination. - By this time, bacteria introduced during surgery have already adhered to tissues and begun forming biofilms.
Question 2: Which of the following disorders would be more likely associated with Staphylococcus saprophyticus rather than Staphylococcus aureus?
- A. Burns
- B. Tension pneumothorax
- C. Osteomyelitis
- D. Acute cystitis (Correct Answer)
Explanation: ***Acute cystitis*** - **Staphylococcus saprophyticus** is a common cause of **urinary tract infections (UTIs)**, particularly acute cystitis, in young sexually active women. - This bacterium has a high affinity for **uroepithelial cells**, facilitating its colonization and subsequent infection of the bladder. *Tension pneumothorax* - A **tension pneumothorax** is a medical emergency characterized by air accumulation in the pleural space, leading to lung collapse and mediastinal shift. - It is typically caused by trauma or iatrogenic factors, not directly by bacterial infection from either *Staphylococcus saprophyticus* or *Staphylococcus aureus*. *Burns* - Burn wounds are highly susceptible to bacterial colonization and infection, with **Staphylococcus aureus** being a primary pathogen in this context. - *Staphylococcus saprophyticus* is rarely associated with burn wound infections. *Osteomyelitis* - **Osteomyelitis**, an infection of the bone, is most frequently caused by **Staphylococcus aureus** via hematogenous spread or direct inoculation. - *Staphylococcus saprophyticus* is not a common pathogen in osteomyelitis.
Question 3: Which of the following is the drug of choice for preoperative antibiotic prophylaxis in a patient undergoing cardiac surgery?
- A. Cefazolin (Correct Answer)
- B. Penicillin
- C. Clindamycin
- D. Vancomycin
Explanation: ***Cefazolin*** - **Cefazolin** is a first-generation cephalosporin that provides excellent coverage against **Staphylococcus aureus** and **Streptococcus species**, which are common pathogens in surgical site infections in cardiac surgery. - It has a favorable safety profile, long half-life allowing for convenient dosing, and good tissue penetration, making it the preferred choice for **preoperative antibiotic prophylaxis** in most cardiac surgery cases. *Penicillin* - **Penicillin** has a narrow spectrum of activity compared to cefazolin and does not adequately cover all potential pathogens in cardiac surgery, particularly **methicillin-susceptible Staphylococcus aureus (MSSA)**. - Due to its limited spectrum, penicillin is generally not recommended for routine **surgical prophylaxis**, especially in complex procedures like cardiac surgery. *Clindamycin* - **Clindamycin** is an alternative for patients with **beta-lactam allergies**, providing coverage against gram-positive organisms and anaerobes. - However, for routine prophylaxis without a specific allergy or high risk of resistant organisms, **clindamycin** is less effective than cefazolin against the most prevalent surgical pathogens. *Vancomycin* - **Vancomycin** is reserved for patients with a known **penicillin allergy** or a high risk of **methicillin-resistant Staphylococcus aureus (MRSA)** colonization or infection. - Its routine use as a primary prophylactic agent in cardiac surgery is discouraged to prevent the development of **vancomycin resistance**.
Question 4: What is the term for bacteria that are actively dividing and have invaded the wound surface in the context of surgical site infection?
- A. Contamination
- B. Colonization
- C. Local infection
- D. Infection (Correct Answer)
Explanation: ***Infection*** - This term precisely describes bacteria that are **actively dividing** and have **invaded the host tissue**, causing a clinical infection with tissue damage and host immune response. - In surgical site infections, this represents the stage where microorganisms have overcome host defenses and are causing disease. - This is the standard terminology used in surgical literature to describe the progression from contamination to active disease. *Contamination* - **Contamination** refers to the presence of microorganisms on a surface or in a wound without active proliferation or host response. - It's an early stage where bacteria are present but not yet multiplying or causing disease. *Colonization* - **Colonization** indicates that microorganisms are replicating on the host surface or in a wound without tissue invasion or causing an immune response. - Unlike infection, colonization does not involve invasion of tissue or clinical signs of disease. *Local infection* - While this describes an infection confined to a particular anatomical area, it is a descriptor of the **location** rather than the **process** described in the question. - The question asks specifically about the term for dividing and invading bacteria, which is simply "infection" - the word "local" adds information about location but doesn't define the fundamental process.
Question 5: When do we have to start antibiotics to prevent post-operative infection?
- A. 1 week before surgery
- B. 2 days before surgery
- C. After surgery
- D. 30-60 minutes before incision (up to 24 hours post-op) (Correct Answer)
Explanation: ***30-60 minutes before incision (up to 24 hours post-op)*** - Surgical antibiotic prophylaxis (SAP) should be administered **30-60 minutes before surgical incision** to ensure adequate tissue and serum concentrations at the time of incision. - This timing allows optimal drug distribution to surgical tissues, which is crucial for preventing surgical site infections (SSIs). - For most clean and clean-contaminated surgeries, prophylaxis should be limited to a **single dose** or continued for **maximum 24 hours post-operatively** as per WHO and CDC guidelines. - Prolonged post-operative antibiotics beyond 24 hours do **not** reduce infection rates and increase the risk of **antibiotic resistance** and **adverse effects**. *1 week before surgery* - Administering antibiotics this far in advance is **unnecessary** and **ineffective** for surgical prophylaxis. - It increases the risk of **antibiotic resistance** and does not guarantee adequate drug levels at the time of incision. - Pre-operative antibiotic use should be avoided unless treating an active infection. *2 days before surgery* - This timeframe is too early to achieve prophylactic benefit during the surgical procedure. - Prolonged pre-operative use promotes **bacterial resistance** without providing additional protection. - Drug levels will not be optimal at the time of incision due to metabolism and excretion. *After surgery* - Starting antibiotics **after surgical incision** is **too late** for prophylaxis as contamination has already occurred. - Post-operative initiation is considered **therapeutic treatment** for established infection, not prevention. - The critical window for prophylaxis is the period from skin incision to wound closure.
Question 6: What is the most common cause of postoperative fever within 24 hours?
- A. Sepsis
- B. Deep vein thrombosis
- C. Atelectasis (Correct Answer)
- D. Wound infection
Explanation: ***Atelectasis*** - **Atelectasis** is the most common cause of **postoperative fever** within the **first 24-48 hours** after surgery. - It results from the collapse of a portion of the lung, usually due to shallow breathing and reduced sigh reflexes under anesthesia, leading to **inflammation** and a mild fever. *Sepsis* - **Sepsis** is a systemic inflammatory response to infection and typically presents with a **high fever**, **tachycardia**, and **hypotension**. - While serious, it is rare for sepsis to manifest as the *most common cause* of fever within the first 24 hours, usually requiring more time for bacterial growth and systemic spread. *Deep vein thrombosis* - **Deep vein thrombosis (DVT)** typically causes fever *later* in the postoperative course, often **3-7 days after surgery**, and is characterized by leg pain, swelling, and redness. - Fever associated with DVT is usually due to the inflammatory response to the clot itself or a resulting **pulmonary embolism**, not an immediate post-operative complication. *Wound infection* - **Wound infections** usually develop **4-7 days postoperatively**, as this timeframe is needed for bacterial proliferation and the inflammatory response to become clinically apparent. - Early fevers (<24 hours) are rarely due to wound infection unless there is significant contamination during surgery, which is uncommon.
Question 7: 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 8: Preferred time for prophylactic antibiotic administration for surgery?
- A. 1 day before surgery
- B. At the time of induction of anaesthesia (Correct Answer)
- C. I.V. during surgery
- D. I.M. 6 hrs before surgery
Explanation: ***At the time of induction of anaesthesia*** - This timing ensures that a **therapeutic concentration** of the antibiotic is present in the tissues at the time of the initial surgical incision, when the risk of bacterial contamination is highest. - Administering the antibiotic too early or too late can reduce its effectiveness in preventing **surgical site infections (SSIs)**. *1 day before surgery* - Administering antibiotics a day before surgery would lead to the drug being **metabolized and eliminated** from the body before the surgical incision is made, rendering it ineffective for prophylaxis. - This timing also increases the risk of **antibiotic resistance** development without providing adequate protection against SSIs. *I.V. during surgery* - Administering the antibiotic intravenously during surgery means that the drug will not have reached sufficient **tissue concentrations** at the crucial moment of the initial incision. - The protective effect is largely dependent on adequate tissue levels **prior to contamination**, which would not be achieved by administration only during the procedure. *I.M. 6 hrs before surgery* - While closer to the optimal timing than 1 day before, administering intramuscularly 6 hours prior may result in **suboptimal drug levels** at the time of incision, especially for drugs with shorter half-lives. - Intramuscular administration can also have variable absorption rates compared to intravenous, potentially delaying peak tissue concentration and reducing reliability for **prophylactic efficacy**.
Question 9: Percentage of surgical site infection in patients with a clean-contaminated wound after prophylactic antibiotic administration?
- A. 1-2%
- B. 10-20%
- C. <10% (Correct Answer)
- D. 20-30%
Explanation: ***<10%*** - For **clean-contaminated wounds**, the rate of surgical site infection (SSI) is generally maintained **below 10%** with proper prophylactic antibiotic administration. - This low percentage reflects the effectiveness of **antibiotic prophylaxis** in preventing SSIs in wounds where controlled entry into a viscus is made. *1-2%* - This range is more typical for **clean wounds** where no viscus is entered, and the risk of contamination is minimal. - Prophylactic antibiotics are highly effective in clean wounds, leading to a very low infection rate. *10-20%* - This percentage is generally considered high for clean-contaminated wounds and may indicate suboptimal antibiotic prophylaxis, an underlying patient risk factor, or a technical surgical issue. - The goal of prophylactic antibiotics is to keep the infection rate well below this range for this wound class. *20-30%* - An infection rate in this range is typically seen in **contaminated** or **dirty wounds**, or in cases where no antibiotics were given. - Such high rates would be unacceptable for a clean-contaminated procedure with appropriate prophylaxis.
Question 10: Which of the following is true about tenosynovitis of the finger?
- A. Treatment is conservative.
- B. Fingers held in mild extension / Extension deformity at the involved fingers.
- C. With involvement of little finger the infection can spread to the ring finger.
- D. Tenosynovitis of little finger will spread to thumb rather than ring finger. (Correct Answer)
Explanation: ***Tenosynovitis of little finger will spread to thumb rather than ring finger.*** - The **little finger's flexor tendon sheath** connects directly to the **ulnar bursa**, which communicates with the **radial bursa** (thumb's sheath) in approximately **80% of individuals** through the space of Parona. - This **bursal communication** creates a direct pathway for infection spread from the little finger to the thumb, making it the most common route of propagation in flexor tenosynovitis. *With involvement of little finger the infection can spread to the ring finger.* - While anatomically possible through **fascial plane connections**, direct spread to the ring finger is **less common** than spread to the thumb via established bursal pathways. - The **ulnar bursa-radial bursa connection** provides a more direct and frequently utilized route for infection propagation than lateral spread to adjacent digits. *Treatment is conservative.* - **Purulent flexor tenosynovitis** requires urgent **surgical incision and drainage** to prevent irreversible tendon damage and loss of function. - Conservative treatment with antibiotics alone is inadequate for established infections and may lead to **tendon necrosis** and permanent disability. *Fingers held in mild extension / Extension deformity at the involved fingers.* - Patients with tenosynovitis characteristically hold the affected finger in **mild flexion** as part of **Kanavel's four cardinal signs**. - **Extension** of the finger causes severe pain due to stretching of the inflamed tendon sheath, so patients avoid this position naturally.
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