Catheter-associated urinary tract infections — MCQs

10 questions

A 62-year-old man comes to the physician because of a 2-day history of fever, chills, and flank pain. Five days ago, he was catheterized for acute urinary retention. His temperature is 39.3°C (102.7°F). Physical examination shows right-sided costovertebral angle tenderness. Urine studies show numerous bacteria and WBC casts. Urine culture on blood agar grows mucoid, gray-white colonies. Urine culture on eosin methylene blue agar grows purple colonies with no metallic green sheen. Which of the following is the most likely causal pathogen?

A 26-year-old female presents to her primary care physician concerned that she has contracted a sexually transmitted disease. She states that she is having severe pain whenever she urinates and seems to be urinating more frequently than normal. She reports that her symptoms started after she began having unprotected sexual intercourse with 1 partner earlier this week. The physician obtains a urinalysis which demonstrates the following, SG: 1.010, Leukocyte esterase: Positive, Nitrites: Positive, Protein: Trace, pH: 5.0, RBC: Negative. A urease test is performed which is negative. This patient has most likely been infected with which of the following organisms?

A 25-year-old woman comes to the physician because of a 2-day history of a burning sensation when urinating and increased urinary frequency. She is concerned about having contracted a sexually transmitted disease. Physical examination shows suprapubic tenderness. Urinalysis shows a negative nitrite test and positive leukocyte esterases. Urine culture grows organisms that show resistance to novobiocin on susceptibility testing. Which of the following is the most likely causal organism of this patient's symptoms?

An 87-year-old woman is brought to the emergency department from her nursing home because of increasing confusion and lethargy for 12 hours. The nursing home aide says she did not want to get out of bed this morning and seemed less responsive than usual. She has Alzheimer's disease, hypertension, and a history of nephrolithiasis. She has chronic, intractable urinary incontinence, for which she has an indwelling urinary catheter. Current medications include galantamine, memantine, and ramipril. Her temperature is 38.5°C (101.3°F), pulse is 112/min, respiratory rate is 16/min, and blood pressure is 108/76 mm Hg. Physical examination shows mild tenderness to palpation of the lower abdomen. On mental status examination, she is oriented only to person. Laboratory studies show: Hemoglobin 12.4 g/dL Leukocyte count 9,000/mm3 Platelet count 355,000/mm3 Urine pH 8.2 Glucose 1+ Protein 2+ Ketones negative RBC 5/hpf WBC 35/hpf Bacteria moderate Nitrites positive Which of the following is the most likely causal organism?

Five days after admission into the ICU for drug-induced acute kidney injury, a 27-year-old woman develops fever. She is currently on a ventilator and sedatives. Hemodialysis is performed via a catheter placed in the right internal jugular vein. Feeding is via a nasogastric tube. An indwelling urinary catheter shows minimum output. Her blood pressure is 85/45 mm Hg, the pulse is 112/min, the respirations are 32/min, and the temperature is 39.6°C (103.3°F). The examination of the central catheter shows erythema around the insertion site with no discharge. Lung auscultation shows rhonchi. Cardiac examination shows no new findings. A chest CT scan shows bilateral pleural effusions with no lung infiltration. Empirical antibiotic therapy is initiated. Blood cultures obtained from peripheral blood and the catheter tip show S. aureus with a similar antibiogram. Urinary culture obtained from the indwelling catheter shows polymicrobial growth. Which of the following best explains this patient’s recent findings?

A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

A 23-year-old woman presents with fever, chills, nausea, and urinary urgency and frequency. She says that her symptoms began 4 days ago and have progressively worsened. Her past medical history is significant for a 6-month history of recurrent urinary tract infections (UTIs). Her vital signs include: temperature 39.0°C (102.2°F), blood pressure 100/70 mm Hg, pulse 92/min, and respiratory rate 25/min. On physical examination, there is moderate left costovertebral angle tenderness. Laboratory findings are significant for the following: WBC 8,500/mm3 RBC 4.20 x 106/mm3 Hematocrit 41.5% Hemoglobin 13.0 g/dL Platelet count 225,000/mm3 Urinalysis Color Dark yellow Clarity Turbid pH 6.5 Specific gravity 1.026 Glucose None Ketones None Nitrites Positive Leukocyte esterase Positive Bilirubin Negative Urobilirubin 0.6 mg/dL Protein Trace Blood None WBC 25/hpf Bacteria Many Which of the following is the most likely diagnosis in this patient?

A 67-year-old man is brought to the emergency department because of severe dyspnea and orthopnea for 6 hours. He has a history of congestive heart disease and an ejection fraction of 40%. The medical history is otherwise unremarkable. He appears confused. At the hospital, his blood pressure is 165/110 mm Hg, the pulse is 135/min, the respirations are 48/min, and the temperature is 36.2°C (97.2°F). Crackles are heard at both lung bases. There is pitting edema from the midtibia to the ankle bilaterally. The patient is intubated and admitted to the critical care unit for mechanical ventilation and treatment. Intravenous morphine, diuretics, and nitroglycerine are initiated. Which of the following is the most effective method to prevent nosocomial infection in this patient?

A previously healthy 24-year-old woman comes to the physician because of a 1-day history of nausea and weakness. She is sexually active with 2 male partners and uses an oral contraceptive; she uses condoms inconsistently. Her last menstrual period was 4 days ago. Her temperature is 38.4°C (101°F). Physical examination shows right costovertebral angle tenderness. Pelvic examination is normal. Which of the following is the most likely cause of this patient's condition?

Q10

Six days after undergoing an elective hip replacement surgery, a 79-year-old man develops dysuria, flank pain, and fever. His temperature is 38.5°C (101.3°F). Examination shows marked tenderness in the right costovertebral area. Treatment with an antibiotic is begun, but his symptoms do not improve. Further evaluation shows that the causal organism produces an enzyme that inactivates the antibiotic via phosphorylation. An agent from which of the following classes of antibiotics was most likely administered?

Catheter-associated urinary tract infections US Medical PG Practice Questions and MCQs

Question 1: A 62-year-old man comes to the physician because of a 2-day history of fever, chills, and flank pain. Five days ago, he was catheterized for acute urinary retention. His temperature is 39.3°C (102.7°F). Physical examination shows right-sided costovertebral angle tenderness. Urine studies show numerous bacteria and WBC casts. Urine culture on blood agar grows mucoid, gray-white colonies. Urine culture on eosin methylene blue agar grows purple colonies with no metallic green sheen. Which of the following is the most likely causal pathogen?

A. Escherichia coli
B. Klebsiella pneumoniae (Correct Answer)
C. Pseudomonas aeruginosa
D. Proteus mirabilis
E. Staphylococcus saprophyticus

Explanation: ***Klebsiella pneumoniae*** - The presence of **mucoid, gray-white colonies** on blood agar and **purple colonies with no metallic green sheen** on EMB agar, along with a history of catheterization, fever, and flank pain strongly suggests *Klebsiella pneumoniae*. - *Klebsiella* is a common cause of **catheter-associated UTIs** and often produces mucoid colonies due to its capsule. *Escherichia coli* - *E. coli* typically produces **metallic green sheen** on EMB agar due to rapid lactose fermentation, which is absent in this case. - While *E. coli* is a common cause of UTIs, the specific culture findings differentiate it from *Klebsiella*. *Pseudomonas aeruginosa* - *Pseudomonas* often produces a **grape-like odor** and distinctive **blue-green pigment** on agar, neither of which is mentioned. - It does not ferment lactose and would thus not produce purple colonies on EMB, but rather appear as colorless or clear colonies. *Proteus mirabilis* - *Proteus mirabilis* is known for its **swarming motility** on agar, which creates a characteristic spreading growth pattern, not merely mucoid colonies. - It also produces **urease**, which can lead to alkaline urine and struvite stones, but the distinguishing colony morphology is not met. *Staphylococcus saprophyticus* - *Staphylococcus saprophyticus* is a **Gram-positive coccus** and would not grow purple colonies on EMB agar, which is selective for Gram-negative bacteria. - It is a common cause of UTIs in young, sexually active women, which does not fit the patient's demographic.

Question 2: A 26-year-old female presents to her primary care physician concerned that she has contracted a sexually transmitted disease. She states that she is having severe pain whenever she urinates and seems to be urinating more frequently than normal. She reports that her symptoms started after she began having unprotected sexual intercourse with 1 partner earlier this week. The physician obtains a urinalysis which demonstrates the following, SG: 1.010, Leukocyte esterase: Positive, Nitrites: Positive, Protein: Trace, pH: 5.0, RBC: Negative. A urease test is performed which is negative. This patient has most likely been infected with which of the following organisms?

A. Enterobacter cloacae
B. Staphylococcus saprophyticus
C. Proteus mirabilis
D. Klebsiella pneumoniae
E. Escherichia coli (Correct Answer)

Explanation: ***Escherichia coli*** - The urinalysis findings of **positive leukocyte esterase**, **nitrites**, and **trace protein** with a slightly acidic pH (5.0) are highly suggestive of a **urinary tract infection (UTI)**. - *E. coli* is the most common cause of UTIs, especially in young, sexually active women, and is typically **urease-negative**, consistent with the information provided. - *E. coli* accounts for **80-90% of uncomplicated UTIs** and produces nitrites from dietary nitrates, making it the most likely pathogen in this clinical scenario. *Enterobacter cloacae* - While *Enterobacter cloacae* can cause UTIs, it is less common than *E. coli* in uncomplicated cases and is often associated with nosocomial infections or those in immunocompromised individuals. - Its urease activity can vary, so a negative urease test doesn't rule it out completely but makes *E. coli* a more likely primary choice in this context. *Staphylococcus saprophyticus* - *S. saprophyticus* is a common cause of UTIs in young, sexually active women (second most common cause after *E. coli*) and is typically **urease-negative**, which is consistent with the negative test. - However, the presence of **positive nitrites** points more strongly towards **Gram-negative bacteria** like *E. coli*, as *S. saprophyticus* is a **Gram-positive coccus** that does not produce nitrite reductase and therefore does not convert nitrates to nitrites. *Proteus mirabilis* - *Proteus mirabilis* is known for causing UTIs and is characteristically **urease-positive**, leading to alkaline urine (higher pH) and sometimes **struvite stones**. - The **negative urease test** and acidic urine pH (5.0) in this case effectively rule out *Proteus mirabilis*. *Klebsiella pneumoniae* - *Klebsiella pneumoniae* can cause UTIs and is generally **urease-negative**, but it is less frequently the cause of uncomplicated UTIs compared to *E. coli*. - Although it can produce nitrites, *E. coli* remains the most common etiology in this clinical scenario.

Question 3: A 25-year-old woman comes to the physician because of a 2-day history of a burning sensation when urinating and increased urinary frequency. She is concerned about having contracted a sexually transmitted disease. Physical examination shows suprapubic tenderness. Urinalysis shows a negative nitrite test and positive leukocyte esterases. Urine culture grows organisms that show resistance to novobiocin on susceptibility testing. Which of the following is the most likely causal organism of this patient's symptoms?

A. Klebsiella pneumoniae
B. Proteus mirabilis
C. Pseudomonas aeruginosa
D. Staphylococcus epidermidis
E. Staphylococcus saprophyticus (Correct Answer)

Explanation: ***Staphylococcus saprophyticus*** - This organism is the **second most common cause of UTIs in young, sexually active women** (after *E. coli*), making it highly consistent with the patient's demographics and presentation. - *S. saprophyticus* is characterized by **resistance to novobiocin**, which is the key laboratory test differentiating it from *S. epidermidis* (novobiocin-sensitive). - It is **nitrite-negative** as it does not reduce nitrates to nitrites, consistent with the negative nitrite test. *Klebsiella pneumoniae* - While *K. pneumoniae* can cause UTIs, it is typically **nitrite-positive** because it reduces nitrates to nitrites, which contradicts the negative nitrite test result. - This gram-negative organism would not be tested for novobiocin susceptibility, as this antibiotic is used specifically to differentiate staphylococcal species. *Proteus mirabilis* - *P. mirabilis* is known for causing UTIs and is **nitrite-positive** due to its ability to reduce nitrates, which is inconsistent with the patient's negative nitrite test. - It also produces **urease**, leading to alkaline urine and struvite stones, which are not features of this acute presentation. *Pseudomonas aeruginosa* - *P. aeruginosa* is **nitrite-negative** (it does not reduce nitrates), which matches the test result. - However, it is typically associated with **hospital-acquired UTIs**, catheter-related infections, or infections in immunocompromised patients, not uncomplicated community-acquired UTIs in healthy young women. - Novobiocin testing is not routinely used for gram-negative organisms. *Staphylococcus epidermidis* - *S. epidermidis* is a common **skin commensal** and frequent contaminant in urine cultures. - Critically, it is **novobiocin-sensitive**, which distinguishes it from *S. saprophyticus* and makes it incompatible with the culture findings. - It rarely causes true UTIs unless associated with indwelling catheters or prosthetic devices.

Question 4: An 87-year-old woman is brought to the emergency department from her nursing home because of increasing confusion and lethargy for 12 hours. The nursing home aide says she did not want to get out of bed this morning and seemed less responsive than usual. She has Alzheimer's disease, hypertension, and a history of nephrolithiasis. She has chronic, intractable urinary incontinence, for which she has an indwelling urinary catheter. Current medications include galantamine, memantine, and ramipril. Her temperature is 38.5°C (101.3°F), pulse is 112/min, respiratory rate is 16/min, and blood pressure is 108/76 mm Hg. Physical examination shows mild tenderness to palpation of the lower abdomen. On mental status examination, she is oriented only to person. Laboratory studies show: Hemoglobin 12.4 g/dL Leukocyte count 9,000/mm3 Platelet count 355,000/mm3 Urine pH 8.2 Glucose 1+ Protein 2+ Ketones negative RBC 5/hpf WBC 35/hpf Bacteria moderate Nitrites positive Which of the following is the most likely causal organism?

A. Enterococcus faecalis
B. Klebsiella pneumoniae
C. Staphylococcus saprophyticus
D. Escherichia coli
E. Proteus mirabilis (Correct Answer)

Explanation: ***Proteus mirabilis*** - The high urine pH (8.2), positive nitrites, and moderate bacteria, along with signs of infection in an elderly catheterized patient, are highly suggestive of a **urea-splitting organism**. - **Proteus mirabilis** is a common cause of catheter-associated UTIs and produces urease, leading to alkaline urine and the formation of struvite stones, consistent with the patient's history of nephrolithiasis. *Enterococcus faecalis* - While *Enterococcus faecalis* can cause UTIs, it typically does not produce urease and therefore would not cause such a **markedly elevated urine pH** (above 7.5). - Although it can cause positive nitrites, the absence of a strong alkali pH makes it less likely than *Proteus mirabilis*. *Klebsiella pneumoniae* - *Klebsiella pneumoniae* can cause UTIs and produce nitrites, but it is not typically a strong **urease producer** to the extent that would cause an alkaline urine pH of 8.2. - It is more commonly associated with nosocomial infections, but the highly alkaline urine points away from it as the most likely cause here. *Staphylococcus saprophyticus* - *Staphylococcus saprophyticus* is a common cause of UTIs in young, sexually active women, but it is **rare in elderly, catheterized patients**. - It is also not typically associated with such a high urine pH as seen in this case. *Escherichia coli* - *Escherichia coli* is the most common cause of UTIs, but it is a **non-urease-producing** bacterium and would typically result in acidic urine, or at least a less alkaline pH than 8.2. - While it would cause positive nitrites and moderate bacteria, the elevated pH makes it less likely than *Proteus mirabilis* in this context.

Question 5: Five days after admission into the ICU for drug-induced acute kidney injury, a 27-year-old woman develops fever. She is currently on a ventilator and sedatives. Hemodialysis is performed via a catheter placed in the right internal jugular vein. Feeding is via a nasogastric tube. An indwelling urinary catheter shows minimum output. Her blood pressure is 85/45 mm Hg, the pulse is 112/min, the respirations are 32/min, and the temperature is 39.6°C (103.3°F). The examination of the central catheter shows erythema around the insertion site with no discharge. Lung auscultation shows rhonchi. Cardiac examination shows no new findings. A chest CT scan shows bilateral pleural effusions with no lung infiltration. Empirical antibiotic therapy is initiated. Blood cultures obtained from peripheral blood and the catheter tip show S. aureus with a similar antibiogram. Urinary culture obtained from the indwelling catheter shows polymicrobial growth. Which of the following best explains this patient’s recent findings?

A. Catheter-associated urinary tract infection
B. Central catheter-related bacteremia (Correct Answer)
C. Endocarditis
D. Ventilator-associated pneumonia
E. Naso-gastric tube sinusitis

Explanation: ***Central catheter-related bacteremia*** - The presence of **erythema at the catheter insertion site** and the isolation of **_S. aureus_ with a similar antibiogram from both peripheral blood and the catheter tip** are highly indicative of a catheter-related bloodstream infection. - This type of infection is common in critically ill patients with central venous catheters due to the direct access provided for bacteria to enter the bloodstream. *Catheter-associated urinary tract infection* - While a **polymicrobial growth** in the urinary culture suggests a urinary tract infection, the isolation of **_S. aureus_ in blood cultures** with signs of local catheter infection points away from the urinary tract as the primary source of bacteremia. - The patient has an **indwelling urinary catheter**, which is a risk factor for UTIs, but the systemic infection with _S. aureus_ is better explained by the central line. *Endocarditis* - Although **_S. aureus_ bacteremia** can lead to endocarditis, the case states that the **cardiac examination shows no new findings**, making endocarditis less likely as the primary explanation for the acute deterioration without other supporting evidence like a new murmur or imaging findings. - Endocarditis is a potential complication of bacteremia, not typically the initial source, especially with a clear source like a central line. *Ventilator-associated pneumonia* - Pulmonary symptoms like **rhonchi** and **bilateral pleural effusions** are present, but the **lack of lung infiltration on CT** and the **isolation of _S. aureus_ from blood and catheter tip** (not respiratory samples) make VAP unlikely to be the primary cause of this systemic infection. - The patient is also on a ventilator, which is a risk factor for VAP, but the microbiologic and imaging evidence does not fully support it as the main diagnosis. *Naso-gastric tube sinusitis* - While nasogastric tubes can cause sinusitis, which could manifest with fever, it is less likely to result in **_S. aureus_ bacteremia with a positive catheter tip culture**. - Sinusitis would explain fever, but not the specific microbiological findings of _S. aureus_ in blood and catheter tip, nor the local erythema at the catheter site.

Question 6: A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

A. "Does the diarrhea typically precede the constipation, or vice-versa?"
B. "Is the diarrhea foul-smelling?"
C. "Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"
D. "Are the symptoms worse in the morning or at night?"
E. "Can you tell me more about the symptoms you have been experiencing?" (Correct Answer)

Explanation: ***Can you tell me more about the symptoms you have been experiencing?*** - This **open-ended question** encourages the patient to provide a **comprehensive narrative** of their symptoms, including details about onset, frequency, duration, alleviating/aggravating factors, and associated symptoms, which is crucial for diagnosis. - In a patient presenting with vague, intermittent symptoms like alternating constipation and diarrhea, allowing them to elaborate freely can reveal important clues that might not be captured by more targeted questions. *Does the diarrhea typically precede the constipation, or vice-versa?* - While knowing the sequence of symptoms can be helpful in understanding the **pattern of bowel dysfunction**, it is a very specific question that might overlook other important aspects of the patient's experience. - It prematurely narrows the focus without first obtaining a broad understanding of the patient's overall symptomatic picture. *Is the diarrhea foul-smelling?* - Foul-smelling diarrhea can indicate **malabsorption** or **bacterial overgrowth**, which are important to consider in some gastrointestinal conditions. - However, this is a **specific symptom inquiry** that should follow a more general exploration of the patient's symptoms, as it may not be relevant if other crucial details are missed. *Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life* - Quantifying pain intensity is useful for assessing the **severity of discomfort** and monitoring changes over time. - However, for a patient with intermittent rather than acute, severe pain, understanding the **character, location, and triggers** of the pain is often more diagnostically valuable than just a numerical rating initially. *Are the symptoms worse in the morning or at night?* - Diurnal variation can be relevant in certain conditions, such as inflammatory bowel diseases where nocturnal symptoms might be more concerning, or functional disorders whose symptoms might be stress-related. - This is another **specific question** that should come after gathering a more complete initial picture of the patient's symptoms to ensure no key information is overlooked.

Question 7: A 23-year-old woman presents with fever, chills, nausea, and urinary urgency and frequency. She says that her symptoms began 4 days ago and have progressively worsened. Her past medical history is significant for a 6-month history of recurrent urinary tract infections (UTIs). Her vital signs include: temperature 39.0°C (102.2°F), blood pressure 100/70 mm Hg, pulse 92/min, and respiratory rate 25/min. On physical examination, there is moderate left costovertebral angle tenderness. Laboratory findings are significant for the following: WBC 8,500/mm3 RBC 4.20 x 106/mm3 Hematocrit 41.5% Hemoglobin 13.0 g/dL Platelet count 225,000/mm3 Urinalysis Color Dark yellow Clarity Turbid pH 6.5 Specific gravity 1.026 Glucose None Ketones None Nitrites Positive Leukocyte esterase Positive Bilirubin Negative Urobilirubin 0.6 mg/dL Protein Trace Blood None WBC 25/hpf Bacteria Many Which of the following is the most likely diagnosis in this patient?

A. Acute obstructing nephrolithiasis
B. Pyelonephritis (Correct Answer)
C. Uncomplicated cystitis
D. Complicated cystitis
E. Renal abscess

Explanation: ***Pyelonephritis*** - The patient presents with **fever, chills, nausea, and costovertebral angle tenderness**, indicating an upper urinary tract infection. - **Urinalysis shows nitrites, leukocyte esterase, WBCs (25/hpf), and many bacteria**, all consistent with infection that has spread to the kidneys. - The **history of recurrent UTIs** increases risk for ascending infection. *Acute obstructing nephrolithiasis* - While **kidney stones** can cause similar pain, this patient's presentation includes **significant fever, chills, and positive signs of infection (nitrites, leukocyte esterase, WBCs in urine)**, which are not typical for uncomplicated nephrolithiasis. - **Hematuria** would be a more prominent finding with nephrolithiasis, and it is absent here ("Blood None"). *Uncomplicated cystitis* - **Cystitis** is a lower urinary tract infection, typically presenting with **dysuria, frequency, and urgency** without systemic symptoms like fever and chills. - The presence of **fever, chills, nausea, and costovertebral angle tenderness** points to an upper UTI (pyelonephritis), not cystitis alone. *Complicated cystitis* - **Complicated cystitis** refers to bladder infection in patients with underlying conditions (e.g., pregnancy, diabetes, urological abnormalities) or recurrent infections. - However, the presence of **fever, chills, and flank pain (costovertebral angle tenderness)** indicates kidney involvement, distinguishing pyelonephritis from a bladder infection. *Renal abscess* - **Renal abscess** can present with fever and flank pain, similar to pyelonephritis. - However, patients with renal abscess typically appear **more toxic**, have **persistently high fevers despite antibiotics**, and often require **imaging (CT scan) for diagnosis**. - The **clinical presentation and urinalysis findings** are more consistent with acute pyelonephritis, which responds well to antibiotic therapy.

Question 8: A 67-year-old man is brought to the emergency department because of severe dyspnea and orthopnea for 6 hours. He has a history of congestive heart disease and an ejection fraction of 40%. The medical history is otherwise unremarkable. He appears confused. At the hospital, his blood pressure is 165/110 mm Hg, the pulse is 135/min, the respirations are 48/min, and the temperature is 36.2°C (97.2°F). Crackles are heard at both lung bases. There is pitting edema from the midtibia to the ankle bilaterally. The patient is intubated and admitted to the critical care unit for mechanical ventilation and treatment. Intravenous morphine, diuretics, and nitroglycerine are initiated. Which of the following is the most effective method to prevent nosocomial infection in this patient?

A. Nasogastric tube insertion
B. Suprapubic catheter insertion
C. Daily oropharynx decontamination with antiseptic agent (Correct Answer)
D. Daily urinary catheter irrigation with antimicrobial agent
E. Condom catheter placement

Explanation: ***Daily oropharynx decontamination with antiseptic agent*** - **Oropharyngeal decontamination** helps reduce the bacterial load in the oral cavity, which is crucial for preventing **ventilator-associated pneumonia (VAP)** in intubated patients. - Regular cleaning with an antiseptic agent disrupts the formation of **biofilms** and the aspiration of pathogenic bacteria into the lower respiratory tract. *Nasogastric tube insertion* - While a nasogastric tube can be important for nutrition and medication delivery, it does not directly prevent **nosocomial infections** and can even be a source of infection if not properly managed. - It does not address the primary risk of pneumonia or other infections related to intubation and critical illness. *Suprapubic catheter insertion* - A suprapubic catheter is used for drainage of the bladder, but it is an invasive procedure with its own risks of **urinary tract infections (UTIs)** and is not indicated for preventing nosocomial infections in this patient's primary presentation. - It is not a standard method to prevent the most common nosocomial infections in an intubated patient in the ICU. *Daily urinary catheter irrigation with antimicrobial agent* - Irrigating a urinary catheter daily with an antimicrobial agent is **not recommended** as a routine practice to prevent **catheter-associated urinary tract infections (CAUTIs)**. - Such irrigation can disrupt the natural flora and potentially lead to **antimicrobial resistance** or further infection by promoting the growth of resistant organisms. *Condom catheter placement* - A condom catheter is a non-invasive external device used for urinary incontinence in males, but it's generally **less effective** than indwelling catheters for critical care patients requiring precise fluid output monitoring. - It does not address the risk of **VAP**, which is a major concern for intubated patients, and may not be feasible or adequate for all bedridden patients in the ICU.

Question 9: A previously healthy 24-year-old woman comes to the physician because of a 1-day history of nausea and weakness. She is sexually active with 2 male partners and uses an oral contraceptive; she uses condoms inconsistently. Her last menstrual period was 4 days ago. Her temperature is 38.4°C (101°F). Physical examination shows right costovertebral angle tenderness. Pelvic examination is normal. Which of the following is the most likely cause of this patient's condition?

A. Noninfectious inflammation of the bladder
B. Ascending bacteria from the endocervix
C. Decreased renal calcium reabsorption
D. Decreased urinary pH
E. Ascending bacteria from the bladder (Correct Answer)

Explanation: ***Ascending bacteria from the bladder*** - The patient presents with **fever**, **nausea**, **weakness**, and **right costovertebral angle (CVA) tenderness**, which are classic symptoms of **acute pyelonephritis**. - **Pyelonephritis** most commonly results from an **ascending urinary tract infection**, where bacteria (typically *E. coli*) from the bladder travel up the ureters to infect the kidneys. - This accounts for approximately **95% of pyelonephritis cases** in young women. *Noninfectious inflammation of the bladder* - **Noninfectious cystitis** (interstitial cystitis) would not typically present with systemic symptoms like **fever** and **nausea**, or with **CVA tenderness**, which indicates kidney involvement. - Bladder inflammation typically causes dysuria and frequency without systemic signs of infection. *Ascending bacteria from the endocervix* - **Ascending bacteria from the endocervix** can cause **pelvic inflammatory disease (PID)**, which presents with lower abdominal pain, cervical motion tenderness, and vaginal discharge. - While PID can cause fever, the **normal pelvic examination** in this patient rules out this diagnosis, and PID **does not typically cause CVA tenderness**. *Decreased renal calcium reabsorption* - **Decreased renal calcium reabsorption** is associated with **hypercalciuria** and **nephrolithiasis** (kidney stones), which can present with acute flank pain if obstruction occurs. - However, this condition does not explain the **fever** and systemic symptoms characteristic of an acute infectious process. *Decreased urinary pH* - **Decreased urinary pH** (acidic urine) can predispose to certain types of kidney stone formation but is not a direct cause of **pyelonephritis**. - It does not explain the presence of **fever**, **CVA tenderness**, and systemic symptoms indicative of a bacterial kidney infection.

Question 10: Six days after undergoing an elective hip replacement surgery, a 79-year-old man develops dysuria, flank pain, and fever. His temperature is 38.5°C (101.3°F). Examination shows marked tenderness in the right costovertebral area. Treatment with an antibiotic is begun, but his symptoms do not improve. Further evaluation shows that the causal organism produces an enzyme that inactivates the antibiotic via phosphorylation. An agent from which of the following classes of antibiotics was most likely administered?

A. Macrolides
B. Tetracyclines
C. Aminoglycosides (Correct Answer)
D. Glycopeptides
E. Fluoroquinolones

Explanation: ***Aminoglycosides*** - **Aminoglycosides** are commonly inactivated by bacterial enzymes through **phosphorylation**, acetylation, or adenylation, leading to resistance. - The patient's lack of improvement despite antibiotic treatment and the mechanism of inactivation point towards this class of antibiotics. *Macrolides* - **Macrolide resistance** typically involves mechanisms such as modification of the ribosomal binding site (e.g., methylation), drug efflux pumps, or enzymatic inactivation by esterases, not phosphorylation. - While macrolides can treat various infections, their inactivation mechanism is different from what is described. *Tetracyclines* - **Tetracycline resistance** is primarily mediated by bacterial efflux pumps that actively transport the antibiotic out of the cell, or by ribosomal protection proteins that interfere with drug binding. - **Enzymatic inactivation via phosphorylation** is not a characteristic resistance mechanism for tetracyclines. *Glycopeptides* - **Glycopeptide resistance**, particularly to vancomycin, is mainly associated with alterations in the cell wall precursor target (e.g., D-Ala-D-Lac modification), which prevents the antibiotic from binding. - This mechanism is distinct from enzymatic phosphorylation of the antibiotic molecule itself. *Fluoroquinolones* - **Fluoroquinolone resistance** primarily arises from mutations in the genes encoding bacterial DNA gyrase and topoisomerase IV, or via efflux pumps. - There is no significant mechanism of resistance involving direct enzymatic phosphorylation of fluoroquinolone drugs.

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