Common Infections — MCQs
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A 34-year-old man presents with a 3-day history of progressive pain and swelling of his right index finger following a minor cut while gardening. Examination reveals a tender, erythematous, swollen finger with purulent discharge from the nail fold and flexor tenosynovitis. What is the most important immediate management step?
A hospital antimicrobial stewardship team is evaluating the implementation of an intravenous to oral switch policy. Which of the following clinical scenarios represents the most appropriate criterion for IV to oral antimicrobial switch in a patient with severe cellulitis who has been receiving IV flucloxacillin for 3 days?
A 52-year-old woman with recurrent MRSA skin infections has completed decolonisation therapy. According to current UK guidance, what is the recommended decolonisation regimen for MRSA carriage?
A hospital antimicrobial stewardship committee reviews prescribing data showing that the median duration of antibiotic therapy for community-acquired pneumonia has decreased from 9 days to 6 days following implementation of new guidelines. However, 30-day readmission rates for pneumonia have increased from 8% to 14%. Which of the following represents the most appropriate interpretation and response to this data?
A 49-year-old man with poorly controlled type 2 diabetes (HbA1c 98 mmol/mol) presents with a 4-day history of increasing pain, swelling and discharge from his right ear. Examination reveals granulation tissue in the external auditory canal with purulent otorrhoea. He has severe otalgia and right-sided facial nerve weakness (House-Brackmann grade III). Temperature is 38.4°C. CT temporal bone shows soft tissue in the external canal with bone erosion of the mastoid. Which antibiotic regimen provides the most appropriate empirical coverage?
What is the primary mechanism by which antimicrobial stewardship programs reduce healthcare-associated Clostridioides difficile infection rates?
A 71-year-old man with type 2 diabetes presents with a 3-day history of painful swelling of his right lower leg. On examination, there is erythema and oedema extending from mid-calf to ankle, with a clear demarcated edge. Temperature is 37.8°C. His right leg has chronic venous changes with haemosiderin deposition and lipodermatosclerosis. An area of shallow ulceration (2 cm × 1.5 cm) is present on the medial malleolus with fibrinous base and no purulent discharge. Which clinical feature best indicates that systemic antibiotic therapy is required?
A 28-year-old woman presents with a 2-day history of a tender, red lump on her left buttock. On examination, there is a 3 cm × 3 cm fluctuant, erythematous swelling with central purulent pointing. She is systemically well with temperature 37.3°C. The abscess is incised and drained in the Emergency Department with 8 mL of pus evacuated. The wound is packed. What is the most appropriate antibiotic management?
A hospital trust introduces a new antimicrobial stewardship intervention using an electronic prescribing system that automatically prompts prescribers to document indication, planned duration, and review date for all antibiotic prescriptions. Six months post-implementation, audit data shows 92% compliance with documentation but no significant change in overall antibiotic consumption or rates of Clostridioides difficile infection. What does this finding best demonstrate?
A 36-year-old previously healthy man presents with a 16-hour history of severe pain in his left hand following a minor puncture wound sustained while cleaning his aquarium. On examination, the dorsum of his left hand is markedly swollen, erythematous, and exquisitely tender. There are multiple haemorrhagic bullae. Temperature is 38.9°C, heart rate 118 bpm, blood pressure 108/65 mmHg. Blood tests show: WCC 18.4 × 10⁹/L, CRP 168 mg/L, lactate 3.2 mmol/L. What is the most likely causative organism?
Common Infections UK Medical PG Practice Questions and MCQs
Question 41: A 34-year-old man presents with a 3-day history of progressive pain and swelling of his right index finger following a minor cut while gardening. Examination reveals a tender, erythematous, swollen finger with purulent discharge from the nail fold and flexor tenosynovitis. What is the most important immediate management step?
- A. Commence oral flucloxacillin and review in 48 hours
- B. Obtain urgent hand surgery referral for incision and drainage with irrigation (Correct Answer)
- C. Perform bedside incision and drainage in the Emergency Department
- D. Commence intravenous co-amoxiclav and admit for observation
- E. Obtain wound swab for culture and commence oral doxycycline
Explanation: ***Obtain urgent hand surgery referral for incision and drainage with irrigation*** - The clinical presentation of progressive pain, swelling, purulent discharge, and **flexor tenosynovitis** following a minor cut strongly indicates an **infectious flexor tenosynovitis**, which is a surgical emergency. - **Urgent surgical decompression and irrigation** are paramount to prevent irreversible damage to the tendon, such as necrosis, and to preserve hand function. *Commence oral flucloxacillin and review in 48 hours* - Delaying definitive treatment for 48 hours is unacceptable for **infectious flexor tenosynovitis**, as rapid progression of infection can lead to permanent **tendon damage** or loss of function. - **Oral antibiotics** alone are insufficient to manage a closed-space infection requiring mechanical debridement and drainage. *Perform bedside incision and drainage in the Emergency Department* - **Flexor tenosynovitis** requires a formal surgical approach in an operating room to ensure complete **irrigation of the entire tendon sheath** and to avoid damaging vital neurovascular structures. - A bedside incision may be inadequate for thorough drainage and carries a high risk of complications, including incomplete infection resolution and injury to adjacent structures. *Commence intravenous co-amoxiclav and admit for observation* - While **intravenous antibiotics** are an important adjunct, they cannot replace the need for **surgical drainage** of the pus in a closed-space infection. - Observation without surgical intervention in cases of **flexor tenosynovitis** will lead to continued pressure and inflammation, resulting in tendon necrosis and permanent functional impairment. *Obtain wound swab for culture and commence oral doxycycline* - **Doxycycline** is not the appropriate empiric antibiotic for typical acute hand infections, which are commonly caused by **Staphylococcus aureus** or **Streptococcus species**. - Waiting for **culture results** before initiating definitive **surgical management** is not advisable for a rapidly progressing infection like **flexor tenosynovitis** due to the risk of irreversible tissue damage.
Question 42: A hospital antimicrobial stewardship team is evaluating the implementation of an intravenous to oral switch policy. Which of the following clinical scenarios represents the most appropriate criterion for IV to oral antimicrobial switch in a patient with severe cellulitis who has been receiving IV flucloxacillin for 3 days?
- A. Temperature normalised for 24 hours, clinical improvement evident, tolerating oral intake, and C-reactive protein decreased by 25% from admission (Correct Answer)
- B. Temperature reduced from 39.2°C to 37.8°C, white cell count decreased from 16 to 12 × 10⁹/L, but patient still reporting significant pain
- C. Complete resolution of erythema and swelling, patient ambulatory, but temperature still 37.9°C on day 3
- D. Patient requesting oral therapy, temperature normalised, but C-reactive protein increased from 120 to 145 mg/L
- E. Clinical improvement noted by nursing staff, temperature 37.2°C, but patient has one episode of vomiting in the past 24 hours
Explanation: ***Temperature normalised for 24 hours, clinical improvement evident, tolerating oral intake, and C-reactive protein decreased by 25% from admission*** - This scenario meets the core **clinical stability** criteria, including being **afebrile** for at least 24 hours and showing clear signs of **infection resolution**. - Successful switch requires a functional **gastrointestinal tract** to ensure adequate **bioavailability** and absorption of the oral antibiotic, alongside improving inflammatory markers like **CRP**. *Temperature reduced from 39.2°C to 37.8°C, white cell count decreased from 16 to 12 × 10⁹/L, but patient still reporting significant pain* - The patient is not yet **afebrile**, as a temperature of 37.8°C indicates a low-grade fever, failing the **temperature normalization** criterion. - Persistent **significant pain** suggests the local infection is not sufficiently controlled or resolving adequately to transition away from **parenteral therapy**. *Complete resolution of erythema and swelling, patient ambulatory, but temperature still 37.9°C on day 3* - A persistent fever of 37.9°C remains an **exclusion criterion** for IV to oral switch according to most **antimicrobial stewardship** guidelines, indicating ongoing systemic infection. - While local physical signs have improved, the systemic **inflammatory response** has not fully subsided, which is crucial for a safe switch. *Patient requesting oral therapy, temperature normalised, but C-reactive protein increased from 120 to 145 mg/L* - An **increasing C-reactive protein (CRP)** level suggests a failure of the current regimen or an escalating **inflammatory process**, which contradicts clinical improvement and warrants further investigation. - Decisions for switch should be based on **objective clinical data** and biochemical trends rather than solely on **patient preference**, even if the temperature is normal. *Clinical improvement noted by nursing staff, temperature 37.2°C, but patient has one episode of vomiting in the past 24 hours* - Any active **vomiting** or significant gastrointestinal upset is a contraindication as it jeopardizes the **gastric absorption** and **bioavailability** of oral medications. - Reliable **oral intake** for at least 24 hours without gastrointestinal distress is generally required to ensure **therapeutic efficacy** after the switch.
Question 43: A 52-year-old woman with recurrent MRSA skin infections has completed decolonisation therapy. According to current UK guidance, what is the recommended decolonisation regimen for MRSA carriage?
- A. Mupirocin nasal ointment three times daily for 5 days and chlorhexidine body wash daily for 5 days (Correct Answer)
- B. Fusidic acid nasal ointment twice daily for 7 days and povidone-iodine body wash daily for 7 days
- C. Mupirocin nasal ointment twice daily for 10 days and triclosan body wash daily for 10 days
- D. Bacitracin nasal ointment three times daily for 5 days and benzalkonium chloride body wash daily for 5 days
- E. Polymyxin B nasal spray twice daily for 7 days and chlorhexidine body wash daily for 7 days
Explanation: ***Mupirocin nasal ointment three times daily for 5 days and chlorhexidine body wash daily for 5 days*** - This regimen reflects the standard **UK NICE and PHE guidelines** for MRSA decolonisation, targeting **MRSA reservoirs** in the nose and on the skin. - The protocol specifically uses 2% **mupirocin** applied to the inner vestibule of both nostrils **three times daily** for **5 days**, combined with **chlorhexidine** body wash. *Fusidic acid nasal ointment twice daily for 7 days and povidone-iodine body wash daily for 7 days* - **Fusidic acid** is generally not recommended as a first-line nasal decolonisation agent due to concerns about rapid development of bacterial **resistance**. - The recommended duration for standard decolonisation is typically **5 days**, not 7, and **povidone-iodine** is not the routinely specified antiseptic wash in UK guidelines. *Mupirocin nasal ointment twice daily for 10 days and triclosan body wash daily for 10 days* - While **mupirocin** is correct, the frequency of **twice daily** is insufficient for optimal efficacy; the standard is **three times daily**. - A **10-day duration** is unnecessarily prolonged for initial decolonisation and **triclosan** is not the standard body wash compared to chlorhexidine in current UK protocols. *Bacitracin nasal ointment three times daily for 5 days and benzalkonium chloride body wash daily for 5 days* - **Bacitracin** is not a standard component of UK MRSA decolonisation regimens due to its inferior efficacy compared to **mupirocin**. - **Benzalkonium chloride** is not the primary recommended antiseptic for **skin decolonisation** in MRSA carriers according to current UK guidance. *Polymyxin B nasal spray twice daily for 7 days and chlorhexidine body wash daily for 7 days* - **Polymyxin B** is primarily active against **Gram-negative bacteria** and is therefore ineffective against **Gram-positive MRSA**. - Nasal sprays are typically not as effective as ointments for decolonisation because they do not consistently coat the **nasal vestibule**, which is the main carriage site.
Question 44: A hospital antimicrobial stewardship committee reviews prescribing data showing that the median duration of antibiotic therapy for community-acquired pneumonia has decreased from 9 days to 6 days following implementation of new guidelines. However, 30-day readmission rates for pneumonia have increased from 8% to 14%. Which of the following represents the most appropriate interpretation and response to this data?
- A. The shorter duration is causing treatment failure and guidelines should be revised to recommend 9-day courses
- B. Further investigation is required to determine if readmissions are causally related to shorter antibiotic duration or reflect other factors (Correct Answer)
- C. The increase in readmissions is an acceptable trade-off for reduced antimicrobial consumption
- D. All patients should have extended antibiotic courses until the readmission rate returns to baseline
- E. The data confirms that antimicrobial stewardship interventions compromise patient safety
Explanation: ***Further investigation is required to determine if readmissions are causally related to shorter antibiotic duration or reflect other factors***- A **temporal association** between shorter antibiotic courses and increased readmission suggests a safety signal, but **correlation does not equal causation**.- Investigating underlying factors like **illness severity**, **patient demographics**, or **microbiology of relapse** is essential before concluding the stewardship intervention is at fault.*The shorter duration is causing treatment failure and guidelines should be revised to recommend 9-day courses*- Reverting to longer courses prematurely ignores the potential for **confounding variables** that could be driving the increase in readmission rates.- Current guidelines for **community-acquired pneumonia (CAP)** generally support shorter courses (5-7 days), so an immediate shift back to 9 days without proof of failure is not **evidence-based practice**.*The increase in readmissions is an acceptable trade-off for reduced antimicrobial consumption*- Antimicrobial stewardship aims to balance **efficacy and safety**; patient safety should never be compromised for the sake of reduced consumption.- Ignoring an increase in **30-day readmission rates** would be a failure of the monitoring phase of any clinical intervention.*All patients should have extended antibiotic courses until the readmission rate returns to baseline*- Implementing **blanket extended courses** lacks clinical precision and exposes many patients to unnecessary **antibiotic side effects** and risk of **C. difficile**.- Effective stewardship requires a **targeted approach**, identifying which specific subgroups might be failing rather than altering therapy for all patients.*The data confirms that antimicrobial stewardship interventions compromise patient safety*- Stewardship is designed to optimize outcomes; while this data indicates a **safety signal**, it does not prove that stewardship inherently compromises care.- Proper stewardship involves the **continuous monitoring** of patient safety data to refine protocols and ensure that optimal care is maintained while reducing resistance.
Question 45: A 49-year-old man with poorly controlled type 2 diabetes (HbA1c 98 mmol/mol) presents with a 4-day history of increasing pain, swelling and discharge from his right ear. Examination reveals granulation tissue in the external auditory canal with purulent otorrhoea. He has severe otalgia and right-sided facial nerve weakness (House-Brackmann grade III). Temperature is 38.4°C. CT temporal bone shows soft tissue in the external canal with bone erosion of the mastoid. Which antibiotic regimen provides the most appropriate empirical coverage?
- A. Intravenous ciprofloxacin (Correct Answer)
- B. Oral ciprofloxacin and topical gentamicin drops
- C. Intravenous piperacillin-tazobactam and ciprofloxacin
- D. Intravenous flucloxacillin and metronidazole
- E. Intravenous ceftazidime
Explanation: ***Intravenous ciprofloxacin*** - The clinical presentation of severe otalgia, **granulation tissue**, bone erosion on CT, and **facial nerve palsy** in a diabetic patient confirms **malignant otitis externa** (necrotising otitis externa). - **Ciprofloxacin** is the first-line treatment as it provides specific and potent activity against **Pseudomonas aeruginosa**, which causes over 90% of cases, and has excellent **bone penetration**. *Oral ciprofloxacin and topical gentamicin drops* - While oral quinolones have high bioavailability, **intravenous administration** is the preferred initial choice for severe cases involving **cranial nerve palsy** and systemic symptoms like fever. - **Topical therapy** alone or as an adjunct is insufficient to treat the deep-seated **skull base osteomyelitis** associated with this condition. *Intravenous piperacillin-tazobactam and ciprofloxacin* - **Dual antipseudomonal therapy** is generally not required for empirical treatment of malignant otitis externa and increases the risk of **adverse effects** and drug resistance. - Piperacillin-tazobactam lacks the specific **pharmacokinetic benefits** of fluoroquinolones for treating chronic bone infections unless multidrug resistance is confirmed. *Intravenous flucloxacillin and metronidazole* - This regimen targets **Staphylococcus aureus** and **anaerobes**, which are not the primary pathogens in necrotising otitis externa. - It provides inadequate coverage against **Pseudomonas aeruginosa**, leading to a high risk of treatment failure and disease progression. *Intravenous ceftazidime* - Although ceftazidime has strong **antipseudomonal activity**, it is usually reserved for cases resistant to ciprofloxacin or when quinolones are contraindicated. - It is less practical for the long-term treatment (typically 6–8 weeks) required for this condition because it lacks an **oral step-down formulation** with equivalent efficacy.
Question 46: What is the primary mechanism by which antimicrobial stewardship programs reduce healthcare-associated Clostridioides difficile infection rates?
- A. Reducing overall antimicrobial consumption, particularly broad-spectrum agents (Correct Answer)
- B. Increasing use of probiotics alongside antibiotic therapy
- C. Improving hand hygiene compliance among healthcare workers
- D. Implementing universal contact precautions for all patients receiving antibiotics
- E. Routine screening of all admitted patients for asymptomatic C. difficile carriage
Explanation: ***Reducing overall antimicrobial consumption, particularly broad-spectrum agents***- Antimicrobial stewardship primarily works by preserving the **normal gut flora**, which provides **colonization resistance** against *C. difficile* spores.- Reducing the use of high-risk agents known as the **'4 Cs'** (**clindamycin, cephalosporins, co-amoxiclav, and carbapenems/fluoroquinolones**) significantly lowers the risk of *C. difficile* overgrowth and toxin production.*Increasing use of probiotics alongside antibiotic therapy*- While some studies suggest potential benefits, clinical guidelines provide **insufficient evidence** to recommend probiotics as a standard primary prevention mechanism within stewardship programs.- Stewardship focuses on **rationalizing drug use** and minimizing harm from antibiotics, rather than primarily relying on adjunctive therapies.*Improving hand hygiene compliance among healthcare workers*- This is a critical **infection control** measure aimed at preventing the physical transmission of spores, but it is distinct from the primary focus of **antimicrobial stewardship** on antibiotic prescribing.- Specifically, *C. difficile* spores are resistant to **alcohol-based hand rubs**, requiring **soap and water** for physical removal.*Implementing universal contact precautions for all patients receiving antibiotics*- Universal contact precautions are **impractical** and not cost-effective; guidelines usually recommend precautions only for patients with **active diarrhea** due to *C. difficile*.- This strategy focuses on containing transmission rather than addressing the underlying **antibiotic pressure** that predisposes patients to infection.*Routine screening of all admitted patients for asymptomatic C. difficile carriage*- Identifying **asymptomatic carriers** is not routinely recommended because treatment of carriers does not prevent disease and can worsen **dysbiosis**.- Screening does not address the core stewardship goal of reducing the **selective advantage** antibiotics provide to *C. difficile* within the host microbiome.
Question 47: A 71-year-old man with type 2 diabetes presents with a 3-day history of painful swelling of his right lower leg. On examination, there is erythema and oedema extending from mid-calf to ankle, with a clear demarcated edge. Temperature is 37.8°C. His right leg has chronic venous changes with haemosiderin deposition and lipodermatosclerosis. An area of shallow ulceration (2 cm × 1.5 cm) is present on the medial malleolus with fibrinous base and no purulent discharge. Which clinical feature best indicates that systemic antibiotic therapy is required?
- A. The presence of chronic venous changes including lipodermatosclerosis
- B. The presence of a venous leg ulcer in the affected area
- C. The acute spreading erythema with systemic temperature elevation (Correct Answer)
- D. The patient's history of type 2 diabetes mellitus
- E. The haemosiderin deposition indicating chronic venous insufficiency
Explanation: ***The acute spreading erythema with systemic temperature elevation***- The presence of **acute spreading erythema** combined with **systemic symptoms** such as fever (37.8°C) is diagnostic of **cellulitis**, which requires systemic antibiotic therapy.- It is essential to distinguish between **bacterial colonization** of a chronic wound and a true **spreading infection** where antibiotics are indicated.*The presence of chronic venous changes including lipodermatosclerosis*- These findings indicate **chronic venous insufficiency** and are not markers of an acute infectious process requiring antibiotics.- While **lipodermatosclerosis** can cause redness (stasis dermatitis), it is generally bilateral and lacks the **acute onset** and fever associated with infection.*The presence of a venous leg ulcer in the affected area*- A **venous leg ulcer** is a risk factor and portal of entry for infection, but its presence alone only indicates **bacterial colonization**.- Routine use of systemic antibiotics for **non-infected ulcers** is discouraged as it does not improve healing and promotes **antimicrobial resistance**.*The patient's history of type 2 diabetes mellitus*- **Diabetes mellitus** is a significant risk factor for complications and severe infections, but it is not a direct indication for starting antibiotics.- Antibiotic therapy must be based on **clinical signs of infection** rather than comorbidities alone.*The haemosiderin deposition indicating chronic venous insufficiency*- **Haemosiderin deposition** is a permanent skin discoloration caused by red blood cell breakdown in the setting of **venous hypertension**.- This is a feature of **long-term venous disease** and does not represent an acute inflammatory or infectious state.
Question 48: A 28-year-old woman presents with a 2-day history of a tender, red lump on her left buttock. On examination, there is a 3 cm × 3 cm fluctuant, erythematous swelling with central purulent pointing. She is systemically well with temperature 37.3°C. The abscess is incised and drained in the Emergency Department with 8 mL of pus evacuated. The wound is packed. What is the most appropriate antibiotic management?
- A. Prescribe oral flucloxacillin for 7 days
- B. No antibiotics required - incision and drainage is sufficient treatment (Correct Answer)
- C. Prescribe oral co-amoxiclav for 5 days
- D. Send pus for culture and await results before deciding on antibiotics
- E. Prescribe oral doxycycline for 5 days
Explanation: ***No antibiotics required - incision and drainage is sufficient treatment*** - For a simple **cutaneous abscess** in an immunocompetent patient without systemic symptoms, **incision and drainage (I&D)** is the gold standard and definitive treatment. - Clinical guidelines (e.g., NICE, IDSA) confirm that antibiotics do not improve cure rates or speed up recovery once **source control** (drainage) is achieved in otherwise healthy individuals. *Prescribe oral flucloxacillin for 7 days* - **Flucloxacillin** targets Gram-positive bacteria like *Staphylococcus aureus*, common in skin infections, but it offers no additional benefit for a simple abscess that has already been successfully drained. - Unnecessary antibiotic use promotes **antimicrobial resistance** and can lead to adverse effects, making it inappropriate for this clinical scenario. *Prescribe oral co-amoxiclav for 5 days* - **Co-amoxiclav** is a broad-spectrum antibiotic, generally reserved for more complex infections or those involving a wider range of pathogens, not a simple localized abscess in a **systemically well** patient. - Antibiotics are typically only considered if there is significant **surrounding cellulitis**, systemic signs of sepsis, or if the patient is **immunocompromised**. *Send pus for culture and await results before deciding on antibiotics* - While **microbiology cultures** of pus are often collected for surveillance or in cases of treatment failure, they are not usually needed to guide initial management for a simple, successfully drained abscess. - Given that **incision and drainage** is curative for this presentation, delaying treatment decisions pending culture results is unnecessary and would not alter the primary management strategy. *Prescribe oral doxycycline for 5 days* - **Doxycycline** is effective against community-acquired **MRSA** and could be considered in areas with high MRSA prevalence or in penicillin-allergic patients, but neither factor is specified here. - Regardless of the specific antibiotic, the definitive treatment for a simple abscess without systemic involvement remains **incision and drainage** alone.
Question 49: A hospital trust introduces a new antimicrobial stewardship intervention using an electronic prescribing system that automatically prompts prescribers to document indication, planned duration, and review date for all antibiotic prescriptions. Six months post-implementation, audit data shows 92% compliance with documentation but no significant change in overall antibiotic consumption or rates of Clostridioides difficile infection. What does this finding best demonstrate?
- A. Electronic prescribing systems are ineffective for antimicrobial stewardship
- B. Documentation compliance alone does not necessarily translate into improved antimicrobial prescribing behaviour (Correct Answer)
- C. The intervention should be abandoned as it has failed to meet its objectives
- D. Clostridioides difficile rates are unrelated to antimicrobial stewardship interventions
- E. Six months is insufficient time to detect meaningful changes in antimicrobial consumption
Explanation: ***Documentation compliance alone does not necessarily translate into improved antimicrobial prescribing behaviour***- This finding highlights the gap between **process measures** (like documentation) and **outcome measures** (like antibiotic consumption or infection rates).- While the electronic system achieved high compliance in data entry, it did not significantly impact **clinical decision-making** or actual prescribing practices, indicating a passive intervention's limitation.*Electronic prescribing systems are ineffective for antimicrobial stewardship*- Electronic prescribing systems are powerful tools for **antimicrobial stewardship** when integrated with robust clinical decision support, alerts, or mandatory review processes.- The ineffectiveness in this scenario lies with the **design of the intervention** (merely prompting documentation), not the inherent capability of the electronic system itself.*The intervention should be abandoned as it has failed to meet its objectives*- Abandoning the intervention is premature, as the high documentation compliance shows a successful **infrastructure implementation**.- The intervention should instead be **refined** by adding more active components, such as automatic alerts for inappropriate prescriptions or requiring specialist approval.*Clostridioides difficile rates are unrelated to antimicrobial stewardship interventions*- This statement is medically incorrect; there is a well-established and direct link between **antibiotic use**, especially **broad-spectrum** agents, and the incidence of **Clostridioides difficile infection**.- The lack of change in C. difficile rates in this case is due to the intervention's failure to reduce **overall antibiotic consumption**, rather than a lack of relationship.*Six months is insufficient time to detect meaningful changes in antimicrobial consumption*- Significant changes in **antimicrobial consumption** can often be detected within a few months, particularly with impactful and effective interventions.- The 92% compliance rate suggests that the intervention was fully adopted and operational; therefore, the lack of change points to a flaw in the **intervention's strategy** rather than merely insufficient time.
Question 50: A 36-year-old previously healthy man presents with a 16-hour history of severe pain in his left hand following a minor puncture wound sustained while cleaning his aquarium. On examination, the dorsum of his left hand is markedly swollen, erythematous, and exquisitely tender. There are multiple haemorrhagic bullae. Temperature is 38.9°C, heart rate 118 bpm, blood pressure 108/65 mmHg. Blood tests show: WCC 18.4 × 10⁹/L, CRP 168 mg/L, lactate 3.2 mmol/L. What is the most likely causative organism?
- A. Streptococcus pyogenes
- B. Vibrio vulnificus
- C. Mycobacterium marinum
- D. Aeromonas hydrophila (Correct Answer)
- E. Erysipelothrix rhusiopathiae
Explanation: ***Aeromonas hydrophila*** - **Aeromonas hydrophila** is a Gram-negative rod found in **freshwater environments** (like aquariums) that causes rapidly progressive soft tissue infections, including **necrotizing fasciitis**. - The presence of **haemorrhagic bullae**, rapid onset within hours, and systemic toxicity (fever, tachycardia, hypotension, elevated WCC, CRP, lactate) in the context of freshwater exposure is classic for this organism. *Vibrio vulnificus* - While it causes similar severe infections with **haemorrhagic bullae** and rapid progression, it is specifically associated with **seawater or saltwater** and raw seafood exposure. - This patient was cleaning a **freshwater aquarium**, making Aeromonas a more statistically likely pathogen than Vibrio. *Mycobacterium marinum* - Known as "**fish tank granuloma**," this infection typically presents as a **chronic**, slow-growing granulomatous lesion or sporotrichoid spread. - It develops over **weeks or months**, not as an acute, fulminant necrotizing infection with systemic sepsis. *Erysipelothrix rhusiopathiae* - This organism causes **erysipeloid**, a localized skin infection typically seen in fishermen or butchers after handling **raw meat or fish**. - It usually presents as a well-defined **purple-red lesion** on the hand that lacks systemic toxicity and typically does not form bullae. *Streptococcus pyogenes* - While **Group A Streptococcus** (GAS) is a leading cause of necrotizing fasciitis and sepsis, it is not specifically associated with **aquarium-related puncture wounds**. - Although clinically similar, the specific **environmental exposure** provided in the history strongly points toward a water-associated Gram-negative rod.
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