Campylobacter jejuni — MCQs

10 questions

A 16-year-old male with no significant past medical, surgical, or family history presents to his pediatrician with new symptoms following a recent camping trip. He notes that he went with a group of friends and 1 other group member is experiencing similar symptoms. Over the past 5 days, he endorses significant flatulence, nausea, and greasy, foul-smelling diarrhea. He denies tenesmus, urgency, and bloody diarrhea. The blood pressure is 118/74 mm Hg, heart rate is 88/min, respiratory rate is 14/min, and temperature is 37.0°C (98.6°F). Physical examination is notable for mild, diffuse abdominal tenderness. He has no blood in the rectal vault. What is the patient most likely to report about his camping activities?

An 18-year-old female returning from a trip to a developing country presents with diarrhea and pain in the abdominal region. Microscopic evaluation of the stool reveals the presence of RBC's and WBC's. The patient reports poor sewage sanitation in the region she visited. The physician suspects a bacterial infection and culture reveals Gram-negative rods that are non-lactose fermenting. The A subunit of the bacteria's toxin acts to:

A 10-year-old girl is brought to the emergency department because of a 2-day history of bloody diarrhea and abdominal pain. Four days ago, she visited a petting zoo with her family. Her temperature is 39.4°C (102.9°F). Abdominal examination shows tenderness to palpation of the right lower quadrant. Stool cultures at 42°C grow colonies that turn black after adding phenylenediamine. Which of the following best describes the most likely causal organism?

A 31-year-old man comes to the physician because of a 2-day history of nausea, abdominal discomfort, and yellow discoloration of the eyes. Six weeks ago, he had an episode of fever, joint pain, swollen lymph nodes, and an itchy rash on his trunk and extremities that persisted for 1 to 2 days. He returned from a backpacking trip to Colombia two months ago. His temperature is 39°C (101.8°F). Physical examination shows scleral icterus. Infection with which of the following agents is the most likely cause of this patient's 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 59-year-old woman comes to the emergency department because of abdominal pain and bloody diarrhea that began 12 hours ago. Three days ago, she ate undercooked chicken at a local restaurant. Blood cultures grow spiral and comma-shaped, oxidase-positive organisms at 42°C. This patient is at greatest risk for which of the following complications?

An investigator studying DNA replication in Campylobacter jejuni inoculates a strain of this organism into a growth medium that contains radiolabeled thymine. After 2 hours, the rate of incorporation of radiolabeled thymine is measured as a proxy for the rate of DNA replication. The cells are then collected by centrifugation and suspended in a new growth medium that lacks ribonucleotides. After another 2 hours, the rate of incorporation of radiolabeled thymine is measured again. The new growth medium directly affects the function of which of the following enzymes?

A 27-year-old woman comes to the physician for a 1-week-history of painful urination and urinary frequency. She has no history of serious illness and takes no medications. She is sexually active with her boyfriend. Her temperature is 36.7°C (98.1°F). There is no costovertebral angle tenderness. Urine dipstick shows leukocyte esterase. A Gram stain does not show any organisms. Which of the following is the most likely causal pathogen?

A 29-year-old man comes to the physician because of a 3-day history of a swollen right knee. Over the past several weeks, he has had similar episodes affecting the right knee and sometimes also the left elbow, in which the swelling lasted an average of 5 days. He has a history of a rash that subsided 2 months ago. He lives in Connecticut with his wife and works as a landscaper. His temperature is 37.8°C (100°F), pulse is 90/min, respirations are 12/min, and blood pressure is 110/75 mm Hg. Physical examination shows a tender and warm right knee; range of motion is limited by pain. The remainder of the examination shows no abnormalities. His hematocrit is 44%, leukocyte count is 10,300/mm3, and platelet count is 145,000/mm3. Serum electrolyte concentrations are within normal limits. Arthrocentesis is performed and the synovial fluid is cloudy. Gram stain is negative. Analysis of the synovial fluid shows a leukocyte count of 70,000/mm3 and 80% neutrophils. Serologic testing confirms the diagnosis. Which of the following is the most likely cause?

Q10

A 21-year-old man presents to the emergency room complaining of pain upon urination and a watery discharge from his penis. It started a few days ago and has been getting progressively worse. His temperature is 98.0°F (36.7°C), blood pressure is 122/74 mmHg, pulse is 83/min, respirations are 14/min, and oxygen saturation is 98% on room air. Physical exam is notable for a tender urethra with a discharge. Gram stain of the discharge is negative for bacteria but shows many neutrophils. Which of the following is the most likely infectious etiology of this patient's symptoms?

Campylobacter jejuni US Medical PG Practice Questions and MCQs

Question 1: A 16-year-old male with no significant past medical, surgical, or family history presents to his pediatrician with new symptoms following a recent camping trip. He notes that he went with a group of friends and 1 other group member is experiencing similar symptoms. Over the past 5 days, he endorses significant flatulence, nausea, and greasy, foul-smelling diarrhea. He denies tenesmus, urgency, and bloody diarrhea. The blood pressure is 118/74 mm Hg, heart rate is 88/min, respiratory rate is 14/min, and temperature is 37.0°C (98.6°F). Physical examination is notable for mild, diffuse abdominal tenderness. He has no blood in the rectal vault. What is the patient most likely to report about his camping activities?

A. The patient camped as a side excursion from a cruise ship.
B. The patient camped in Mexico.
C. This has been going on for months.
D. Recent antibiotic prescription
E. Collecting water from a stream, without boiling or chemical treatment (Correct Answer)

Explanation: ***Collecting water from a stream, without boiling or chemical treatment*** - The patient's symptoms of **greasy, foul-smelling diarrhea**, flatulence, and nausea following a camping trip are highly suggestive of **giardiasis**. - **Giardiasis** is commonly acquired through the consumption of untreated **contaminated water**, often from streams or lakes in wilderness areas. *The patient camped as a side excursion from a cruise ship.* - While cruise ships can be sources of infectious outbreaks, the specific symptoms of **greasy, foul-smelling diarrhea** are less typical for common cruise-associated infections. - Furthermore, cruise-related illnesses are usually associated with cruise ship facilities rather than **wilderness camping** directly. *The patient camped in Mexico.* - Traveling to Mexico is a risk factor for **traveler's diarrhea**, often caused by bacterial pathogens like ***E. coli***. - However, typical traveler's diarrhea tends to be watery, occasionally bloody, and often presents with fever, which is not consistent with the patient's symptoms of **greasy, foul-smelling diarrhea** and absence of fever. *This has been going on for months.* - The symptoms are described as **new** and have developed over the past 5 days following a recent camping trip, indicating an **acute onset**, not a chronic condition. - Chronic diarrhea lasting for months would point towards other persistent or long-term gastrointestinal issues, not an acute infection from a recent exposure. *Recent antibiotic prescription* - Recent antibiotic use can lead to **antibiotic-associated diarrhea**, most notably ***Clostridioides difficile*** infection. - However, this patient has no history of recent antibiotic prescription, and the specific symptom of **greasy, foul-smelling diarrhea** is not characteristic of *C. difficile* infection.

Question 2: An 18-year-old female returning from a trip to a developing country presents with diarrhea and pain in the abdominal region. Microscopic evaluation of the stool reveals the presence of RBC's and WBC's. The patient reports poor sewage sanitation in the region she visited. The physician suspects a bacterial infection and culture reveals Gram-negative rods that are non-lactose fermenting. The A subunit of the bacteria's toxin acts to:

A. Inhibit exocytosis of ACh from synaptic terminals
B. Lyse red blood cells
C. Prevent phagocytosis
D. Act as an N-glycosidase on 28S rRNA of the 60S ribosome (Correct Answer)
E. ADP-ribosylate the Gs protein

Explanation: ***Act as an N-glycosidase on 28S rRNA of the 60S ribosome*** - The clinical presentation (bloody diarrhea, abdominal pain, exposure to poor sanitation), microscopic findings (RBCs and WBCs in stool), and bacterial characteristics (Gram-negative, non-lactose fermenting rods) point to an infection by **Shigella dysenteriae**. - The **Shiga toxin** produced by *Shigella dysenteriae* is an A-B toxin where the A subunit acts as an **N-glycosidase**, cleaving an adenine residue from the **28S rRNA of the 60S ribosomal subunit**, thereby irreversibly inhibiting protein synthesis and causing cell death. *Inhibit exocytosis of ACh from synaptic terminals* - This mechanism is characteristic of **botulinum toxin**, produced by *Clostridium botulinum*, which primarily affects the nervous system, leading to **flaccid paralysis**, not bloody diarrhea. - The clinical picture and stool findings are inconsistent with botulism. *Lyse red blood cells* - While some bacterial toxins are **hemolysins** and can lyse red blood cells, this is not the primary mechanism of action for the Shiga toxin. - The lysis of RBCs observed in the stool is due to damage to the intestinal lining, not direct lysis by the toxin in the bloodstream. *Prevent phagocytosis* - Many bacterial capsules (e.g., *Streptococcus pneumoniae*) and surface components prevent phagocytosis, but this is a mechanism for evading the immune system, not the direct action of a toxin causing bloody diarrhea by inhibiting protein synthesis. - The question specifically asks about the A subunit's action, which is enzymatic and intracellular. *ADP-ribosylate the Gs protein* - This is the mechanism of action for **cholera toxin** (produced by *Vibrio cholerae*) and **heat-labile enterotoxin** (produced by *Enterotoxigenic E. coli*). - This action leads to continuous activation of **adenylate cyclase** and increased cAMP, resulting in severe **watery diarrhea**, not bloody diarrhea.

Question 3: A 10-year-old girl is brought to the emergency department because of a 2-day history of bloody diarrhea and abdominal pain. Four days ago, she visited a petting zoo with her family. Her temperature is 39.4°C (102.9°F). Abdominal examination shows tenderness to palpation of the right lower quadrant. Stool cultures at 42°C grow colonies that turn black after adding phenylenediamine. Which of the following best describes the most likely causal organism?

A. Gram-positive, anaerobic, rod-shaped bacteria that form spores
B. Gram-positive, aerobic, rod-shaped bacteria that produce catalase
C. Gram-negative, non-flagellated bacteria that do not ferment lactose
D. Gram-negative, flagellated bacteria that do not ferment lactose (Correct Answer)
E. Gram-negative, non-flagellated bacteria that ferment lactose

Explanation: ***Gram-negative, flagellated bacteria that do not ferment lactose*** - The clinical presentation of **bloody diarrhea**, **abdominal pain**, and fever, along with a history of **petting zoo exposure**, strongly suggests a *Campylobacter* infection, which is a **gram-negative, flagellated, curved rod** that does not ferment lactose. - The growth at **42°C (thermophilic)** and a **positive oxidase test** (indicated by colonies turning black after adding phenylenediamine, an oxidase reagent) are characteristic features of *Campylobacter spp*. *Gram-positive, anaerobic, rod-shaped bacteria that form spores* - This description typically refers to organisms like *Clostridium difficile* or *Clostridium perfringens*, which can cause diarrhea. - However, they are **anaerobic** and would not grow well in typical stool culture conditions without specific anaerobic techniques, nor would they produce a positive oxidase test. *Gram-positive, aerobic, rod-shaped bacteria that produce catalase* - This describes organisms like *Listeria monocytogenes* or *Bacillus cereus*. - While *Listeria* can cause gastrointestinal symptoms, it's less commonly associated with the acute, bloody diarrhea and petting zoo exposure seen here, and *Bacillus cereus* typically causes food poisoning with vomiting. *Gram-negative, non-flagellated bacteria that do not ferment lactose* - This description commonly applies to *Shigella spp.* - While *Shigella* causes **bloody diarrhea** and **abdominal pain**, it is typically **non-motile** (non-flagellated), whereas *Campylobacter* is motile due to its flagella. *Gram-negative, non-flagellated bacteria that ferment lactose* - This description would fit organisms like enteropathogenic *E. coli* (EPEC) or enterotoxigenic *E. coli* (ETEC). - However, the specific growth conditions (thermophilic) and positive oxidase test pointed to by phenylenediamine reactivity are not characteristic of these organisms.

Question 4: A 31-year-old man comes to the physician because of a 2-day history of nausea, abdominal discomfort, and yellow discoloration of the eyes. Six weeks ago, he had an episode of fever, joint pain, swollen lymph nodes, and an itchy rash on his trunk and extremities that persisted for 1 to 2 days. He returned from a backpacking trip to Colombia two months ago. His temperature is 39°C (101.8°F). Physical examination shows scleral icterus. Infection with which of the following agents is the most likely cause of this patient's findings?

A. Enterotoxigenic E. coli
B. Hepatitis B (Correct Answer)
C. Borrelia burgdorferi
D. Campylobacter jejuni
E. Hepatitis A

Explanation: ***Hepatitis B*** - This patient's presentation is **classic for acute hepatitis B infection**. The key diagnostic feature is the **serum sickness-like prodrome** that occurred 6 weeks ago, characterized by **fever, arthralgia, lymphadenopathy, and urticarial rash**. - This prodromal syndrome results from **circulating immune complexes** (HBsAg-antibody complexes) and is a **hallmark of Hepatitis B**, occurring in 10-20% of acute HBV cases during the pre-icteric phase. - The timeline fits perfectly: **exposure 2 months ago** (travel to Colombia) → **prodrome at 6 weeks** (4-10 weeks post-exposure is typical) → **icteric phase now** (jaundice with scleral icterus). - Hepatitis B can be transmitted through **sexual contact, needlestick injuries, or exposure to contaminated instruments** during travel, making it highly relevant in this travel context. *Hepatitis A* - While hepatitis A is common in travelers to endemic areas and causes acute hepatitis, it **does NOT typically present with the serum sickness-like prodrome** described here. - HAV prodrome is usually **nonspecific** (malaise, anorexia, nausea) and does **not include arthralgia, lymphadenopathy, or urticarial rash**. - The described prodromal syndrome with rash and joint pain is **pathognomonic for HBV**, not HAV. *Borrelia burgdorferi* - This bacterium causes **Lyme disease**, characterized by **erythema migrans** (expanding target lesion), not an urticarial rash. - Lyme disease does not cause **acute hepatitis with jaundice** or the icteric presentation seen here. - Not consistent with the clinical timeline or hepatic involvement. *Enterotoxigenic E. coli* - ETEC causes **traveler's diarrhea** with watery stools, cramping, and nausea, typically within days of exposure. - Does **not cause hepatitis**, jaundice, or a prodromal syndrome with rash and arthralgia. - Symptoms resolve within 3-5 days without hepatic involvement. *Campylobacter jejuni* - Causes **bacterial gastroenteritis** with bloody diarrhea, fever, and abdominal pain. - Does **not cause acute hepatitis** with jaundice or the serum sickness-like prodrome described. - While travel-associated, it does not explain the hepatic and systemic findings.

Question 5: 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 6: A 59-year-old woman comes to the emergency department because of abdominal pain and bloody diarrhea that began 12 hours ago. Three days ago, she ate undercooked chicken at a local restaurant. Blood cultures grow spiral and comma-shaped, oxidase-positive organisms at 42°C. This patient is at greatest risk for which of the following complications?

A. Toxic megacolon
B. Segmental myelin degeneration (Correct Answer)
C. Peyer patch necrosis
D. Seizures
E. Erythema nodosum

Explanation: ***Segmental myelin degeneration*** - The description of the organism (spiral/comma-shaped, oxidase-positive, growing at 42°C) combined with bloody diarrhea from undercooked chicken strongly suggests **_Campylobacter jejuni_** infection. - _Campylobacter jejuni_ infection is the most common antecedent infection for **Guillain-Barré syndrome (GBS)**, which is characterized by **segmental demyelination** of peripheral nerves. *Toxic megacolon* - This complication is more commonly associated with severe inflammatory bowel disease or infections like **_Clostridium difficile_** or **_Entamoeba histolytica_**. - While theoretically possible with any severe diarrheal illness, it is not the **greatest risk** specifically linked to _Campylobacter_ in this context. *Peyer patch necrosis* - **Peyer patch necrosis** is a characteristic complication seen in **typhoid fever**, caused by **_Salmonella Typhi_**, which would present differently (e.g., rose spots, bradycardia, step-wise fever). - _Campylobacter_ infection primarily causes inflammation of the intestinal mucosa rather than necrosis of Peyer patches. *Seizures* - Seizures are not a typical or common direct complication of _Campylobacter jejuni_ infection in adults, although severe electrolyte imbalances from any diarrhea could rarely precipitate them. - They are more commonly associated with direct CNS infections or severe systemic inflammatory responses from other pathogens. *Erythema nodosum* - **Erythema nodosum** is a non-specific inflammatory condition that can be associated with various infections, including streptococcal infections, tuberculosis, and some fungal diseases, as well as inflammatory bowel disease. - While it has been reported rarely with _Campylobacter_ infections, it is not the **most significant or common complication** compared to GBS.

Question 7: An investigator studying DNA replication in Campylobacter jejuni inoculates a strain of this organism into a growth medium that contains radiolabeled thymine. After 2 hours, the rate of incorporation of radiolabeled thymine is measured as a proxy for the rate of DNA replication. The cells are then collected by centrifugation and suspended in a new growth medium that lacks ribonucleotides. After another 2 hours, the rate of incorporation of radiolabeled thymine is measured again. The new growth medium directly affects the function of which of the following enzymes?

A. DNA polymerase II
B. Telomerase
C. Primase (Correct Answer)
D. DNA polymerase I
E. Ligase

Explanation: ***Primase*** - **Primase** is an **RNA polymerase** that synthesizes short **RNA primers** required for DNA replication. The new growth medium lacks **ribonucleotides**, which are the building blocks for RNA. - Without **ribonucleotides**, primase cannot synthesize RNA primers, thereby directly affecting its function and subsequently inhibiting DNA replication. *DNA polymerase II* - **DNA polymerase II** is primarily involved in **DNA repair** and translesion synthesis, not in synthesizing the main leading and lagging strands of DNA replication. - Its function is not directly dependent on the availability of **ribonucleotides** for primer synthesis during normal replication. *DNA polymerase I* - **DNA polymerase I** is crucial for removing **RNA primers** and filling in the resulting gaps with DNA nucleotides. - While it acts on the primers made by primase, its direct catalytic activity does not involve synthesizing RNA primers from **ribonucleotides**. *Telomerase* - **Telomerase** is a specialized reverse transcriptase that extends telomeres at the ends of eukaryotic chromosomes. - **Campylobacter jejuni** is a prokaryote and therefore lacks linear chromosomes and **telomeres**, making telomerase irrelevant to its DNA replication. *Ligase* - **Ligase** is an enzyme that joins **Okazaki fragments** and other DNA breaks by forming phosphodiester bonds. - Its function involves sealing nicks in the DNA backbone and does not directly rely on the presence of **ribonucleotides** for creating new primers.

Question 8: A 27-year-old woman comes to the physician for a 1-week-history of painful urination and urinary frequency. She has no history of serious illness and takes no medications. She is sexually active with her boyfriend. Her temperature is 36.7°C (98.1°F). There is no costovertebral angle tenderness. Urine dipstick shows leukocyte esterase. A Gram stain does not show any organisms. Which of the following is the most likely causal pathogen?

A. Escherichia coli
B. Chlamydia trachomatis (Correct Answer)
C. Gardnerella vaginalis
D. Neisseria gonorrhoeae
E. Trichomonas vaginalis

Explanation: ***Chlamydia trachomatis*** - This patient presents with symptoms of **dysuria** and **urinary frequency**, consistent with a **urethritis**. The absence of bacteria on Gram stain points towards an **atypical pathogen**. - **Chlamydia trachomatis** is a common cause of **non-gonococcal urethritis** and is a sexually transmitted infection, which fits with the sexually active history. *Escherichia coli* - **E. coli** is the most common cause of **bacterial urinary tract infections (UTIs)**, but a Gram stain in this case would typically reveal Gram-negative rods. - While it causes dysuria and frequency, the **negative Gram stain** makes it less likely than an atypical pathogen. *Gardnerella vaginalis* - **Gardnerella vaginalis** is associated with **bacterial vaginosis**, causing a characteristic **fishy odor** and **vaginal discharge**, which are not reported here. - It does not typically cause urethritis leading to painful urination and urinary frequency. *Neisseria gonorrhoeae* - **Neisseria gonorrhoeae** can cause **urethritis** with symptoms similar to those presented, and it is a sexually transmitted infection. - However, Gram stain would typically show **Gram-negative diplococci** (intracellularly), which were not observed in this case. *Trichomonas vaginalis* - **Trichomonas vaginalis** is a **protozoan parasite** causing **trichomoniasis**, which commonly presents with **vaginitis** (frothy, green-yellow discharge, itching) or sometimes urethritis. - While it is a **sexually transmitted infection**, this organism is not detected by Gram stain (which only stains bacteria); it would require **wet mount microscopy** for visualization. The primary presentation is usually vaginal, and it's less likely to be the sole cause of these urinary symptoms without other signs of vaginitis.

Question 9: A 29-year-old man comes to the physician because of a 3-day history of a swollen right knee. Over the past several weeks, he has had similar episodes affecting the right knee and sometimes also the left elbow, in which the swelling lasted an average of 5 days. He has a history of a rash that subsided 2 months ago. He lives in Connecticut with his wife and works as a landscaper. His temperature is 37.8°C (100°F), pulse is 90/min, respirations are 12/min, and blood pressure is 110/75 mm Hg. Physical examination shows a tender and warm right knee; range of motion is limited by pain. The remainder of the examination shows no abnormalities. His hematocrit is 44%, leukocyte count is 10,300/mm3, and platelet count is 145,000/mm3. Serum electrolyte concentrations are within normal limits. Arthrocentesis is performed and the synovial fluid is cloudy. Gram stain is negative. Analysis of the synovial fluid shows a leukocyte count of 70,000/mm3 and 80% neutrophils. Serologic testing confirms the diagnosis. Which of the following is the most likely cause?

A. Rheumatoid arthritis
B. Neisseria gonorrhoeae
C. Borrelia burgdorferi (Correct Answer)
D. Campylobacter jejuni
E. Osteoarthritis

Explanation: ***Borrelia burgdorferi*** - The patient's **migratory polyarthritis** (affecting knee and elbow intermittently), history of a **rash** (consistent with erythema migrans), and residence in an **endemic area** (Connecticut) strongly suggest **Lyme disease**. - **Synovial fluid analysis** showing high leukocyte count with neutrophilic predominance is typical of inflammatory arthritis, including Lyme arthritis, and **serologic testing** will confirm the presence of *Borrelia burgdorferi* antibodies. *Rheumatoid arthritis* - While rheumatoid arthritis causes inflammatory polyarthritis, it typically presents with **symmetrical joint involvement**, morning stiffness, and often involves smaller joints first, which is not described. - The presence of a preceding **rash** and resolution within weeks is not characteristic of rheumatoid arthritis. *Neisseria gonorrhoeae* - **Disseminated gonococcal infection** can cause migratory polyarthralgia or septic arthritis, but it is typically associated with a history of recent unprotected sexual activity and often with tenosynovitis or dermatitis (pustular or vesicular lesions). - While gram stain is negative in this case, gonococcal arthritis usually has a more rapid onset and systemic symptoms. *Campylobacter jejuni* - *Campylobacter jejuni* is a common cause of **reactive arthritis**, which can cause inflammatory joint pain after a gastrointestinal infection. - However, reactive arthritis typically involves the **lower extremities** and has a specific pattern of oligoarthritis, often with enthesitis or dactylitis, and the preceding rash and geographical factors do not fit. *Osteoarthritis* - Osteoarthritis is a **degenerative joint disease** characterized by pain that worsens with activity and improves with rest, and typically affects older individuals. - It does not present with a preceding **rash**, migratory inflammatory episodes, or a highly inflammatory synovial fluid (high leukocyte count with neutrophilic predominance).

Question 10: A 21-year-old man presents to the emergency room complaining of pain upon urination and a watery discharge from his penis. It started a few days ago and has been getting progressively worse. His temperature is 98.0°F (36.7°C), blood pressure is 122/74 mmHg, pulse is 83/min, respirations are 14/min, and oxygen saturation is 98% on room air. Physical exam is notable for a tender urethra with a discharge. Gram stain of the discharge is negative for bacteria but shows many neutrophils. Which of the following is the most likely infectious etiology of this patient's symptoms?

A. Chlamydia trachomatis (Correct Answer)
B. Trichomonas vaginalis
C. Neisseria gonorrhoeae
D. Staphylococcus saprophyticus
E. Escherichia coli

Explanation: ***Chlamydia trachomatis*** - The presentation of **dysuria**, **watery discharge**, and a **Gram stain negative for bacteria but positive for neutrophils** is highly characteristic of **non-gonococcal urethritis**, with *Chlamydia trachomatis* being the most common cause. - *Chlamydia* is an **intracellular bacterium** and does not readily stain with Gram stain, explaining the negative result despite the presence of inflammation (neutrophils). *Trichomonas vaginalis* - While *Trichomonas vaginalis* can cause urethritis and discharge in men, it typically presents with **frothy yellow-green discharge** and is less common than *Chlamydia* in male urethritis. - It would also likely be identifiable on a **wet mount microscopy** rather than just a Gram stain negative for bacteria. *Neisseria gonorrhoeae* - **Gonococcal urethritis** typically presents with a **purulent, thick discharge** and would show **Gram-negative diplococci** on Gram stain, which are absent in this case. - The Gram stain finding of "negative for bacteria" specifically rules out *Neisseria gonorrhoeae*. *Staphylococcus saprophyticus* - *Staphylococcus saprophyticus* is a common cause of **urinary tract infections (UTIs)**, especially in young women, but less commonly causes urethritis with discharge in men. - If present, it would likely be detected on a standard **Gram stain** and culture as **Gram-positive cocci**. *Escherichia coli* - *Escherichia coli* is the most common cause of **UTIs** but typically causes **cystitis** or **pyelonephritis** rather than isolated urethritis with discharge in men, unless associated with specific risk factors. - It would appear as **Gram-negative rods** on Gram stain if it were the causative agent and would typically result in a positive bacterial finding.

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