Implant-Related Infections — MCQs
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?
Which organism causes prosthetic valve endocarditis within 60 days of surgery?
The ability of bacteria and microcolonies within biofilm to communicate with one another is?
A 12-year-old girl begins to limp while playing soccer. She has pain in her right leg and upper right thigh. Her temperature is 102°F. X-ray of the femur reveals that the periosteum is eroded. Assuming that this case is managed as an infectious disease, which of the following is the most likely etiologic agent?
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?
A 40-year-old female with multiple sexual partners presented with fever, rash, and articular symptoms. Migratory arthritis and tenosynovitis of knees, hands, wrists, feet, and ankles were noticed during clinical examination. Synovial fluid leukocyte count was 12,000/ml and culture was sterile. The patient has been successfully treated with injection ceftriaxone 1 g Q24 hours for 7 days. What was the diagnosis in this setting?
What will the aspirated synovial fluid in a case of septic arthritis typically show?
Osteosclerosis of bone occurs due to?
What is the usual site of tuberculous bursitis?
Implant-Related Infections Indian Medical PG Practice Questions and MCQs
Question 1: 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 2: Which organism causes prosthetic valve endocarditis within 60 days of surgery?
- A. Staphylococcus aureus
- B. Staphylococcus epidermidis (Correct Answer)
- C. Fungus
- D. Streptococcus viridans
Explanation: ***Staphylococcus epidermidis*** - This organism is the **most common cause of early prosthetic valve endocarditis (within 60 days of surgery)**, accounting for 30-40% of cases. - As a coagulase-negative Staphylococcus, *S. epidermidis* commonly colonizes the skin and can be introduced during the surgical procedure. - It produces **biofilms**, which allow it to adhere to prosthetic surfaces and resist antibiotic treatment. *Staphylococcus aureus* - *Staphylococcus aureus* is the **second most common cause of early prosthetic valve endocarditis** (20-25% of cases) and can cause both early and late infections. - It typically presents with a more **fulminant, aggressive course** compared to *S. epidermidis*. - While both staphylococcal species cause early PVE, *S. epidermidis* remains more frequent. *Fungus* - **Fungal endocarditis** on prosthetic valves (typically *Candida* species) accounts for 5-10% of early PVE cases. - More commonly seen in immunocompromised patients, those with prolonged antibiotic use, or after complicated cardiac surgery. - Its incidence is significantly lower than staphylococcal causes in the early post-operative period. *Streptococcus viridans* - *Streptococcus viridans* is the **most common cause of native valve endocarditis**, particularly in patients with pre-existing valvular heart disease. - It typically causes a **subacute presentation** and is more associated with **late prosthetic valve endocarditis** (>60 days post-surgery), not early PVE. - Rarely implicated in early prosthetic valve infections.
Question 3: The ability of bacteria and microcolonies within biofilm to communicate with one another is?
- A. Transmission
- B. Conjugation
- C. Transformation
- D. Quorum sensing (Correct Answer)
Explanation: ***Quorum sensing*** - **Quorum sensing** is a system of stimuli and response that is correlated to population density, allowing bacteria within a biofilm to **communicate and coordinate their behavior**. - This communication enables bacteria to organize tasks like gene expression, biofilm formation, and virulence factor production once a certain **population density (quorum)** is reached. *Transmission* - **Transmission** describes the spread of a disease or pathogen from one host to another, or from a source to a host. - It does not refer to the internal communication mechanisms between microorganisms within a biofilm. *Conjugation* - **Conjugation** is a mechanism of bacterial gene transfer where genetic material, typically a plasmid, is transferred directly from one bacterium to another through a **pilus**. - While it involves bacterial interaction, it's about gene exchange rather than population-density-dependent communication. *Transformation* - **Transformation** is a process by which bacterial cells take up **naked DNA** from their environment. - This is another mechanism of genetic exchange, distinct from cell-to-cell communication that regulates group behavior based on population density.
Question 4: A 12-year-old girl begins to limp while playing soccer. She has pain in her right leg and upper right thigh. Her temperature is 102°F. X-ray of the femur reveals that the periosteum is eroded. Assuming that this case is managed as an infectious disease, which of the following is the most likely etiologic agent?
- A. Salmonella enteritidis
- B. Staphylococcus saprophyticus
- C. Listeria monocytogenes
- D. Staphylococcus aureus (Correct Answer)
Explanation: ***Staphylococcus aureus*** - *S. aureus* is the most common cause of **osteomyelitis** in children, accounting for the symptoms of bone pain, limp, fever, and periosteal erosion. - The organism frequently gains access to bone via **hematogenous spread** from a superficial infection or direct inoculation through trauma. *Salmonella enteritidis* - While *Salmonella* can cause osteomyelitis, especially in patients with **sickle cell disease**, there is no indication of this predisposing factor in the girl's history. - *Salmonella* osteomyelitis is less common than that caused by *S. aureus* in the general pediatric population. *Staphylococcus saprophyticus* - *S. saprophyticus* is primarily associated with **urinary tract infections (UTIs)**, particularly in young, sexually active females. - It is an uncommon cause of osteomyelitis and typically not the primary pathogen in bone infections. *Listeria monocytogenes* - *Listeria monocytogenes* is known to cause severe infections in **immunocompromised individuals**, neonates, and pregnant women. - While it can cause osteomyelitis, it is a rare cause in an otherwise healthy 12-year-old and would usually be associated with specific risk factors.
Question 5: 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 6: 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 7: A 40-year-old female with multiple sexual partners presented with fever, rash, and articular symptoms. Migratory arthritis and tenosynovitis of knees, hands, wrists, feet, and ankles were noticed during clinical examination. Synovial fluid leukocyte count was 12,000/ml and culture was sterile. The patient has been successfully treated with injection ceftriaxone 1 g Q24 hours for 7 days. What was the diagnosis in this setting?
- A. Disseminated gonococcal infection (Correct Answer)
- B. Gonococcal septic arthritis
- C. Syphilitic arthritis
- D. Arthritis due to Pseudomonas aeruginosa
Explanation: ***Disseminated gonococcal infection*** - The classic triad of **fever**, **rash**, and **articular symptoms (migratory polyarthralgia or tenosynovitis)** in a sexually active individual strongly suggests disseminated gonococcal infection (**DGI**). - The positive response to **ceftriaxone**, an antibiotic effective against *Neisseria gonorrhoeae*, further supports this diagnosis. *Gonococcal septic arthritis* - While *N. gonorrhoeae* can cause septic arthritis, it typically presents as a **monoarticular** joint infection with severe pain and swelling, not **migratory polyarthritis** and tenosynovitis. - The synovial fluid in septic arthritis would show a significantly **higher leukocyte count** (often >50,000 cells/mm³) and frequently a positive culture if bacteria are adequately cultured. *Syphilitic arthritis* - Syphilitic arthritis is uncommon and often presents in **secondary or tertiary syphilis**, characterized by chronic inflammation and unique bone lesions, not acute migratory polyarthritis or tenosynovitis. - The rash of secondary syphilis is typically **macropapular and non-pruritic**, often involving the palms and soles, which differs from the rash seen in DGI. *Arthritis due to Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* arthritis is rare and typically occurs in individuals with **immunocompromise**, **intravenous drug use**, or following **puncture wounds**, none of which are mentioned here. - The clinical picture of **migratory polyarthralgia and tenosynovitis** is not characteristic of *Pseudomonas* arthritis, which is usually purulent and monoarticular.
Question 8: What will the aspirated synovial fluid in a case of septic arthritis typically show?
- A. Clear and straw-colored fluid
- B. Low viscosity fluid
- C. Cloudy or purulent fluid
- D. Markedly increased polymorphonuclear leukocytes (Correct Answer)
Explanation: ***Markedly increased polymorphonuclear leukocytes*** - **Septic arthritis** is characterized by an acute infection within the joint, leading to a profound inflammatory response with a significant influx of **neutrophils** (polymorphonuclear leukocytes) into the synovial fluid. - A synovial leukocyte count greater than **50,000 cells/mm³** with over **75% neutrophils** is highly suggestive of septic arthritis. *Clear and straw-colored fluid* - This description typically corresponds to **normal synovial fluid** or fluid from a mild **non-inflammatory condition**, which is not consistent with bacterial infection. - Normal synovial fluid is usually **transparent**, indicating the absence of significant cellular debris or inflammatory cells. *Low viscosity fluid* - While septic synovial fluid can have reduced viscosity due to the breakdown of **hyaluronic acid** by bacterial enzymes and inflammatory mediators, this characteristic alone is not the most definitive diagnostic feature. - Reduced viscosity is also observed in other inflammatory conditions, making it less specific than direct cellular analysis for diagnosing infection. *Cloudy or purulent fluid* - The presence of **cloudy** or **purulent (pus-like)** fluid *is* often seen in septic arthritis, reflecting the high cell count and protein content. - However, this is a **gross visual observation**, and a more precise and diagnostic indicator is the microscopic finding of markedly increased **polymorphonuclear leukocytes**.
Question 9: Osteosclerosis of bone occurs due to?
- A. Decreased host resistance
- B. Increase in the virulence of organisms causing infection
- C. Increased host response (Correct Answer)
- D. Occurs in immunocompromised patients
Explanation: ### Explanation **Concept Overview:** Osteosclerosis refers to an abnormal increase in bone density, characterized by thickening of the trabeculae and narrowing of the medullary canal. In the context of infections (like chronic osteomyelitis), it represents a **productive or formative bone response** rather than a destructive one. **Why Option C is Correct:** Osteosclerosis occurs when the **host’s immune response is strong** and the infecting organism’s virulence is relatively low. This balance allows the body to contain the infection by stimulating osteoblastic activity, leading to the formation of dense, sclerotic bone. A classic clinical example is **Garré’s Sclerosing Osteomyelitis**, where the body reacts to a low-grade chronic infection by producing massive subperiosteal new bone and sclerosis without significant suppuration or sequestration. **Why Other Options are Incorrect:** * **Options A & D:** Decreased host resistance or an immunocompromised state typically leads to rapid, aggressive bone destruction (osteolysis) and systemic spread, rather than the organized, dense bone formation seen in sclerosis. * **Option B:** High virulence of an organism usually results in acute suppuration, abscess formation, and bone necrosis (sequestrum). Sclerosis is a hallmark of a chronic, low-grade process where the host is "winning" the battle or maintaining a stalemate. **High-Yield Clinical Pearls for NEET-PG:** * **Garré’s Sclerosing Osteomyelitis:** Most common in the mandible and tibia; characterized by "onion-skin" periosteal reaction and dense sclerosis. * **Brodie’s Abscess:** Another form of high host resistance where a subacute infection is localized and walled off by a rim of sclerotic bone. * **Radiological Sign:** On X-ray, osteosclerosis appears as increased radiopacity (whiteness) and loss of the normal trabecular pattern.
Question 10: What is the usual site of tuberculous bursitis?
- A. Prepatellar
- B. Subacromial
- C. Subdeltoid
- D. Trochanteric (Correct Answer)
Explanation: ### Explanation **Correct Option: D. Trochanteric** Tuberculous bursitis is a chronic granulomatous inflammation caused by *Mycobacterium tuberculosis*. Among all the bursae in the human body, the **Trochanteric bursa** (located between the greater trochanter and the gluteus maximus/tensor fasciae latae) is the **most common site** of involvement. The pathogenesis usually involves the hematogenous spread of the bacilli or direct extension from an underlying focus of osteomyelitis in the greater trochanter. Clinically, it presents as a "cold abscess" over the lateral aspect of the hip, often associated with a limp and local tenderness, though hip joint movements usually remain preserved in the early stages. **Why other options are incorrect:** * **A. Prepatellar:** While the prepatellar bursa is a common site for *septic* (pyogenic) or *traumatic* bursitis (Housemaid’s knee), it is rarely affected by tuberculosis. * **B & C. Subacromial and Subdeltoid:** These bursae are occasionally involved in TB, often secondary to tuberculosis of the shoulder joint (Caries Sicca), but they are statistically less common than trochanteric involvement. **Clinical Pearls for NEET-PG:** * **Pathognomonic Sign:** The presence of **"Rice bodies"** (fibrin masses) within the bursal fluid is a classic finding in tuberculous bursitis and rheumatoid arthritis. * **Radiology:** X-rays may show soft tissue swelling and irregular erosions of the greater trochanter (the "hidden" primary focus). * **Treatment:** Management involves a combination of Anti-Tubercular Therapy (ATT) and surgical excision (bursectomy) if the disease is extensive or recalcitrant. * **Differential Diagnosis:** Must be distinguished from "Snapping Hip Syndrome" and Trochanteric Pain Syndrome.
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free