Chlamydia pneumoniae US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Chlamydia pneumoniae. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Chlamydia pneumoniae US Medical PG Question 1: A previously healthy 19-year-old woman comes to the physician because of vaginal discharge for 3 days. She describes the discharge as yellow and mucopurulent with a foul odor. She has also noticed vaginal bleeding after sexual activity. She has not had any itching or irritation. Her last menstrual period was 2 weeks ago. She is sexually active with one male partner, and they use condoms inconsistently. A rapid urine hCG test is negative. Her temperature is 37.3°C (99.1°F), pulse is 88/min, and blood pressure is 108/62 mm Hg. Pelvic examination shows a friable cervix. Speculum examination is unremarkable. A wet mount shows no abnormalities. Which of the following is the most appropriate diagnostic test?
- A. Pap smear
- B. Nucleic acid amplification test (Correct Answer)
- C. Colposcopy
- D. Tzanck smear
- E. Gram stain of cervical swab
Chlamydia pneumoniae Explanation: **Nucleic acid amplification test (NAAT)**
- The patient's symptoms (mucopurulent discharge, postcoital bleeding, friable cervix) are highly suggestive of **cervicitis**, particularly due to **Chlamydia trachomatis** or **Neisseria gonorrhoeae**.
- **NAAT** is the most sensitive and specific diagnostic test for these infections, which are common causes of mucopurulent cervicitis, even when a wet mount is negative.
*Pap smear*
- A **Pap smear** screens for **cervical dysplasia** and **cervical cancer**, not infectious causes of cervicitis.
- While it might coincidentally show inflammatory changes, it is not the primary diagnostic tool for identifying the causative organism of her acute symptoms.
*Colposcopy*
- **Colposcopy** is used for the detailed examination of the cervix, vagina, and vulva when an abnormal Pap smear result suggests **cervical lesions** or cancer.
- It is not indicated for the initial diagnosis of cervicitis unless specific abnormalities that warrant biopsy are identified.
*Tzanck smear*
- A **Tzanck smear** is used to identify **multinucleated giant cells** and **intranuclear inclusions**, characteristic of **herpes simplex virus (HSV)** infection.
- The patient's symptoms (mucopurulent discharge, no itching, no vesicular lesions) are not typical for a primary HSV outbreak.
*Gram stain of cervical swab*
- While a **Gram stain** can identify some bacteria, it has poor sensitivity and specificity for diagnosing **gonococcal** or **chlamydial cervicitis** in women.
- NAATs have largely replaced Gram stain for this purpose due to superior accuracy.
Chlamydia pneumoniae US Medical PG Question 2: A 23-year-old woman presents to the emergency department with abnormal vaginal discharge and itchiness. She states it started a few days ago and has been worsening. The patient has a past medical history of a medical abortion completed 1 year ago. Her temperature is 98.6°F (37.0°C), blood pressure is 129/68 mmHg, pulse is 80/min, respirations are 14/min, and oxygen saturation is 99% on room air. Physical exam demonstrates an anxious woman. Pelvic exam reveals yellow cervical discharge. Nucleic acid amplification test is negative for Neisseria species. Which of the following is the best next step in management?
- A. Ceftriaxone
- B. Azithromycin and ceftriaxone
- C. Fluconazole
- D. Azithromycin (Correct Answer)
- E. Cervical cultures
Chlamydia pneumoniae Explanation: ***Azithromycin***
- A **yellow cervical discharge** and **negative *Neisseria* species NAAT** strongly suggest a *Chlamydia trachomatis* infection, for which azithromycin is a first-line treatment.
- Given the patient's symptoms of **vaginal discharge and itchiness**, along with the high prevalence of chlamydia, empirical treatment is appropriate while awaiting further test results.
*Ceftriaxone*
- This antibiotic is primarily used to treat **gonorrhea**, which has been ruled out by the negative *Neisseria* NAAT.
- While sometimes given in combination therapy, it is not the best single agent in this scenario.
*Azithromycin and ceftriaxone*
- This combination is typically used for **empirical treatment of cervicitis** when both gonorrhea and chlamydia are suspected.
- However, since **gonorrhea has been excluded** by NAAT, adding ceftriaxone is unnecessary at this point.
*Fluconazole*
- Fluconazole is an **antifungal medication** used to treat **yeast infections** (*Candida* species).
- While the patient reports itchiness, a **yellow discharge** is more characteristic of a bacterial infection like chlamydia, rather than the typically white, cottage-cheese-like discharge of a yeast infection.
*Cervical cultures*
- While collecting cervical cultures for other pathogens (e.g., **Trichomonas**) might be considered, the immediate priority in a symptomatic patient with suspected chlamydia is to **initiate treatment to prevent complications** and reduce transmission.
- **NAATs are highly sensitive and specific** for chlamydia and gonorrhea, making them preferred over traditional cultures for these infections.
Chlamydia pneumoniae US Medical PG Question 3: A 23-year-old male comes to the physician because of a 2-week history of fatigue, muscle aches, and a dry cough. He has also had episodes of painful, bluish discoloration of the tips of his fingers, nose, and earlobes during this period. Three months ago, he joined the military and attended basic training in southern California. He does not smoke or use illicit drugs. His temperature is 37.8°C (100°F). Physical examination shows mildly pale conjunctivae and annular erythematous lesions with a dusky central area on the extensor surfaces of the lower extremities. Which of the following is the most likely causal organism?
- A. Chlamydophila pneumoniae
- B. Streptococcus pneumoniae
- C. Mycoplasma pneumoniae (Correct Answer)
- D. Adenovirus
- E. Influenza virus
Chlamydia pneumoniae Explanation: ***Mycoplasma pneumoniae***
- This patient's symptoms (fatigue, muscle aches, dry cough, slightly elevated temperature, and **erythema multiforme**-like lesions) are characteristic of **atypical pneumonia**. The **Raynaud-like phenomenon** (bluish discoloration of fingertips, nose, earlobes) and recent military basic training environment are highly suggestive of *Mycoplasma pneumoniae* infection.
- *Mycoplasma pneumoniae* is a common cause of **atypical pneumonia**, especially in crowded settings like military barracks, and is associated with extrapulmonary manifestations such as **Raynaud's phenomenon**, **hemolytic anemia** (suggested by pale conjunctivae), and **erythema multiforme**.
*Chlamydophila pneumoniae*
- This organism also causes **atypical pneumonia** with a dry cough and constitutional symptoms but is less commonly associated with the prominent extrapulmonary findings like **Raynaud's phenomenon** and **erythema multiforme** seen in this patient.
- While it can cause pharyngitis and hoarseness, the constellation of symptoms, particularly the cutaneous and vascular manifestations, points away from *Chlamydophila pneumoniae*.
*Streptococcus pneumoniae*
- *Streptococcus pneumoniae* typically causes **typical bacterial pneumonia**, characterized by a **productive cough**, high fever, chills, and often **lobar consolidation** on chest X-ray.
- It is not associated with **Raynaud's phenomenon**, **erythema multiforme**, or the specific demographic and exposure history (military basic training for atypical presentation) described.
*Adenovirus*
- **Adenovirus** can cause **respiratory tract infections**, including pharyngitis, conjunctivitis, and pneumonia, often seen in outbreaks in crowded settings.
- However, it is less commonly associated with the dramatic extrapulmonary manifestations like **Raynaud's phenomenon** and **erythema multiforme** that are prominent in this case.
*Influenza virus*
- **Influenza virus** causes a **respiratory illness** with fever, myalgia, fatigue, and cough, but **dry cough** is more common.
- While it can lead to pneumonia, the presence of **Raynaud's phenomenon** and **erythema multiforme** is not a typical presentation of influenza.
Chlamydia pneumoniae US Medical PG Question 4: A 43-year-old woman presents to the emergency department complaining of palpitations, dry cough, and shortness of breath for 1 week. She immigrated to the United States from Korea at the age of 20. She says that her heart is racing and she has never felt these symptoms before. Her cough is dry and is associated with shortness of breath that occurs with minimal exertion. Her past medical history is otherwise unremarkable. She has no allergies and is not currently taking any medications. She is a nonsmoker and an occasional drinker. She denies illicit drug use. Her blood pressure is 100/65 mm Hg, pulse is 76/min, respiratory rate is 23/min, and temperature is 36.8°C (98.2°F). Her physical examination is significant for bibasilar lung crackles and a non-radiating, low-pitched, mid-diastolic rumbling murmur best heard at the apical region. In addition, she has jugular vein distention and bilateral pitting edema in her lower extremities. Which of the following best describes the infectious agent that led to this patient’s condition?
- A. A bacterium that induces partial lysis of red cells with hydrogen peroxide
- B. A bacterium that requires an anaerobic environment to grow properly
- C. A bacterium that does not lyse red cells
- D. A bacterium that induces heme degradation of the red cells of a blood agar plate
- E. A bacterium that induces complete lysis of the red cells of a blood agar plate with an oxygen-sensitive cytotoxin (Correct Answer)
Chlamydia pneumoniae Explanation: ***A bacterium that induces complete lysis of the red cells of a blood agar plate with an oxygen-sensitive cytotoxin***
- This describes **Group A Streptococcus (GAS)**, specifically *Streptococcus pyogenes*, which causes **rheumatic fever** leading to **mitral stenosis**. Mitral stenosis is characterized by a **mid-diastolic rumbling murmur** at the apex, left atrial enlargement causing **palpitations**, and **pulmonary congestion** leading to dyspnea, cough, and bibasilar crackles.
- The delayed onset of symptoms (immigrated at 20, symptoms at 43) is typical for **rheumatic heart disease**, where repeated GAS infections in childhood/adolescence lead to valve damage that manifests years later. GAS produces **streptolysin O**, an **oxygen-labile cytotoxin** responsible for **beta-hemolysis** (complete lysis) on blood agar.
*A bacterium that induces partial lysis of red cells with hydrogen peroxide*
- This describes **alpha-hemolytic** bacteria like *Streptococcus pneumoniae* or *Viridans streptococci*, which cause **partial hemolysis** (greenish discoloration) on blood agar due to **hydrogen peroxide** production.
- While *Viridans streptococci* can cause **infective endocarditis**, the clinical picture of **rheumatic mitral stenosis** is more consistent with a history of recurrent streptococcal pharyngitis (GAS).
*A bacterium that requires an anaerobic environment to grow properly*
- This description typically refers to **anaerobic bacteria**, such as *Clostridium* or *Bacteroides* species.
- These bacteria are generally not associated with the primary cause of acute rheumatic fever or the subsequent development of chronic valvular heart disease like mitral stenosis.
*A bacterium that does not lyse red cells*
- This describes **gamma-hemolytic** (non-hemolytic) bacteria, such as *Enterococcus faecalis* or some *Staphylococcus* species.
- These organisms do not cause the characteristic hemolysis seen with the streptococci responsible for rheumatic fever.
*A bacterium that induces heme degradation of the red cells of a blood agar plate*
- This description is **too vague** and does not specifically identify the organism. While heme degradation occurs with various types of hemolysis, the key distinguishing feature of **Group A Streptococcus** is **complete lysis (beta-hemolysis)** combined with production of the **oxygen-sensitive toxin streptolysin O**.
- This option lacks the specificity needed to identify GAS as the causative agent of rheumatic fever. Both alpha- and beta-hemolytic organisms can degrade heme, but only beta-hemolytic GAS causes rheumatic heart disease.
Chlamydia pneumoniae US Medical PG Question 5: A 45-year-old man visits the office with complaints of severe pain with urination for 5 days. In addition, he reports having burning discomfort and itchiness at the tip of his penis. He is also concerned regarding a yellow-colored urethral discharge that started a week ago. Before his symptoms began, he states that he had sexual intercourse with multiple partners at different parties organized by the hotel he was staying at. Physical examination shows edema and erythema concentrated around the urethral meatus accompanied by a mucopurulent discharge. Which of the following diagnostic tools will best aid in the identification of the causative agent for his symptoms?
- A. Nucleic acid amplification tests (NAATs) (Correct Answer)
- B. Urethral biopsy
- C. Tzanck smear
- D. Leukocyte esterase dipstick test
- E. Gram stain
Chlamydia pneumoniae Explanation: ***Nucleic acid amplification tests (NAATs)***
- NAATs are the **most sensitive and specific diagnostic tools** for detecting common sexually transmitted infections (STIs) like **gonorrhea** and **chlamydia**, which present with urethral discharge, dysuria, and itching.
- They can identify the **genetic material** of the causative organisms directly from urine samples or urethral swabs, making them highly effective even with low bacterial loads.
*Urethral biopsy*
- A urethral biopsy is an **invasive procedure** generally reserved for investigating conditions like **strictures, tumors, or chronic inflammatory diseases** when other diagnostic methods are inconclusive.
- It is not a primary diagnostic tool for acute urethritis suspected to be an STI, as it carries risks and is unnecessary given the availability of less invasive options.
*Tzanck smear*
- The Tzanck smear is primarily used for diagnosing **herpes simplex virus (HSV) infections** by looking for multinucleated giant cells and intranuclear inclusions.
- While HSV can cause genital lesions, it typically does not present as a primary symptom of mucopurulent urethral discharge and dysuria without visible vesicles or ulcers, making it less likely in this scenario.
*Leukocyte esterase dipstick test*
- A leukocyte esterase dipstick test detects the presence of **white blood cells** in urine, indicating inflammation or infection in the urinary tract.
- While it can suggest urethritis, it is **not specific for the causative agent** and merely indicates inflammation, requiring further specific testing to identify the pathogen.
*Gram stain*
- A Gram stain of urethral discharge can rapidly identify Gram-negative intracellular diplococci suggestive of **gonorrhea** (Neisseria gonorrhoeae).
- However, its sensitivity for gonorrhea is lower than NAATs, especially in asymptomatic cases or for detecting other common causes of urethritis like **Chlamydia trachomatis**, which are not visible on Gram stain.
Chlamydia pneumoniae US Medical PG Question 6: Nucleic acid amplification testing (NAAT) of first-void urine confirms infection with Chlamydia trachomatis. Treatment with the appropriate pharmacotherapy is started. Which of the following health maintenance recommendations is most appropriate at this time?
- A. Take medication with food
- B. Avoid sun exposure
- C. Avoid drinking alcohol
- D. Avoid sexual activity for the next month (Correct Answer)
- E. Schedule an ophthalmology consultation
Chlamydia pneumoniae Explanation: ***Avoid sexual activity for the next month***
- **CDC guidelines** recommend abstinence from sexual activity until 7 days after treatment completion AND until all sexual partners have been treated and cured. The recommendation of "the next month" provides adequate time to ensure both conditions are met, as **partner notification**, testing, and treatment often takes several weeks.
- This is the **most important health maintenance recommendation** as preventing **reinfection** and further **transmission** is the primary public health concern, superseding medication-specific advice.
*Take medication with food*
- This recommendation is specific to certain antibiotics to reduce gastrointestinal upset or improve absorption, but it is not a universal health maintenance recommendation for all Chlamydia treatments (e.g., **azithromycin** can be taken with or without food; **doxycycline** should be taken with food to reduce GI upset, but not milk products).
- While relevant to **medication adherence**, it is not the most crucial health maintenance advice regarding preventing transmission or re-infection.
*Avoid sun exposure*
- This advice is primarily given for medications that cause **photosensitivity**, such as **doxycycline**, which is a common treatment for Chlamydia.
- However, it's not applicable to all Chlamydia treatments (e.g., **azithromycin**) and is not the most critical health recommendation in the context of preventing disease transmission.
*Avoid drinking alcohol*
- This is a general recommendation for many antibiotic treatments to prevent potential interactions or increased side effects, but it is not a specific contraindication for the primary antibiotics used for Chlamydia.
- **Metronidazole**, used for other STIs (e.g., trichomoniasis), has a strong interaction with alcohol. However, it's not the primary treatment for Chlamydia, making this recommendation less universally appropriate here.
*Schedule an ophthalmology consultation*
- While Chlamydia can cause **conjunctivitis** (ophthalmia neonatorum in newborns or adult inclusion conjunctivitis), it is not a typical complication requiring routine ophthalmology consultation unless specific **ocular symptoms** are present.
- This recommendation is not a standard health maintenance strategy for **uncomplicated Chlamydia infections**.
Chlamydia pneumoniae US Medical PG Question 7: An endocervical swab is performed and nucleic acid amplification testing via polymerase chain reaction is conducted. It is positive for Chlamydia trachomatis and negative for Neisseria gonorrhoeae. Which of the following is the most appropriate pharmacotherapy?
- A. Oral azithromycin (Correct Answer)
- B. Intramuscular ceftriaxone plus oral azithromycin
- C. Oral doxycycline
- D. Intramuscular ceftriaxone
- E. Intravenous cefoxitin plus oral doxycycline
Chlamydia pneumoniae Explanation: ***Oral azithromycin***
- A single 1-gram oral dose of **azithromycin** is a highly effective and convenient first-line treatment for uncomplicated **Chlamydia trachomatis** infections.
- Its long half-life allows for once-daily dosing, improving patient adherence.
*Intramuscular ceftriaxone plus oral azithromycin*
- This combination therapy is primarily used for suspected or confirmed **gonorrhea** and chlamydia coinfection, particularly if N. gonorrhoeae cannot be ruled out.
- Since **Neisseria gonorrhoeae** was explicitly negative, the ceftriaxone component is unnecessary.
*Oral doxycycline*
- **Doxycycline** (100 mg twice daily for 7 days) is an alternative first-line treatment for **Chlamydia trachomatis** infections and is highly effective.
- However, azithromycin is often preferred for its single-dose regimen which can improve treatment adherence, especially in asymptomatic patients.
*Intramuscular ceftriaxone*
- **Ceftriaxone** is the primary treatment for **Neisseria gonorrhoeae** infections.
- As the test for **N. gonorrhoeae** was negative, this treatment is not indicated for the current patient's diagnosis.
*Intravenous cefoxitin plus oral doxycycline*
- This regimen is typically reserved for more severe infections, such as **pelvic inflammatory disease (PID)**, often requiring hospitalization, which is not indicated by the simple positive chlamydia swab.
- Administering **IV cefoxitin** is an escalation beyond what is necessary for uncomplicated chlamydial cervicitis.
Chlamydia pneumoniae US Medical PG Question 8: A 43-year-old woman comes to the physician because of a fever, nausea, and a nonproductive cough for 7 days. During this period, she has had headaches, generalized fatigue, and muscle and joint pain. She has also had increasing shortness of breath for 2 days. She has type 2 diabetes mellitus and osteoarthritis of her left knee. Current medications include insulin and ibuprofen. She had smoked two packs of cigarettes daily for 20 years but stopped 10 years ago. Her temperature is 38.1°C (100.6°F), pulse is 94/min, respirations are 18/min, and blood pressure is 132/86 mm Hg. The lungs are clear to auscultation. There are multiple skin lesions with a blue livid center, pale intermediate zone, and a dark red peripheral rim on the upper and lower extremities. Laboratory studies show:
Hemoglobin 14.6 g/dL
Leukocyte count 11,100/mm3
Serum
Na+ 137 mEq/L
K+ 4.1 mEq/L
Cl- 99 mEq/L
Urea nitrogen 17 mg/dL
Glucose 123 mg/dL
Creatinine 0.9 mg/dL
Which of the following is the most likely causal organism?
- A. Legionella pneumophila
- B. Mycoplasma pneumoniae (Correct Answer)
- C. Haemophilus influenzae
- D. Klebsiella pneumoniae
- E. Staphylococcus aureus
Chlamydia pneumoniae Explanation: ***Mycoplasma pneumoniae***
- The patient presents with a **nonproductive cough**, **headache**, **fatigue**, **myalgia**, and **arthralgia**, which are classic symptoms of **atypical pneumonia**. The presence of **erythema multiforme** (skin lesions with a blue livid center, pale intermediate zone, and dark red peripheral rim) is also strongly associated with *Mycoplasma pneumoniae* infection.
- While the chest X-ray specifically mentioned is not provided, atypical pneumonias often show **patchy infiltrates** that are out of proportion to the patient's symptoms (walking pneumonia), and the constellation of symptoms strongly points towards *Mycoplasma pneumoniae*.
*Legionella pneumophila*
- While *Legionella* can cause **atypical pneumonia** with gastrointestinal symptoms (**nausea** in this case) and hyponatremia, the prominent skin rash (erythema multiforme) is not a typical feature.
- **Hyponatremia** and **confusion** are more commonly associated with *Legionella*, neither of which are prominent findings here.
*Haemophilus influenzae*
- This typically causes **bacterial pneumonia** with more pronounced purulent sputum and lung consolidation, which is not suggested by the nonproductive cough and clear auscultation.
- While *Haemophilus influenzae* can cause respiratory infections, it is less likely to present with the systemic symptoms and characteristic rash seen in this patient.
*Klebsiella pneumoniae*
- Characteristically causes severe, **lobar pneumonia**, often seen in alcoholics and individuals with chronic lung disease, and is associated with **"currant jelly" sputum**.
- The patient's symptoms (nonproductive cough, systemic symptoms, rash) and the description of the lung auscultation (clear) do not align with a typical *Klebsiella pneumoniae* infection.
*Staphylococcus aureus*
- Can cause severe **necrotizing pneumonia**, often following a viral illness (e.g., influenza), and is associated with multiple cavitations and abscesses on chest imaging.
- While there is a history of smoking, the presentation with diffuse systemic symptoms and erythema multiforme is not typical for **staphylococcal pneumonia**.
Chlamydia pneumoniae US Medical PG Question 9: A previously healthy 27-year-old woman comes to the physician because of a 3-week history of fatigue, headache, and dry cough. She does not smoke or use illicit drugs. Her temperature is 37.8°C (100°F). Chest examination shows mild inspiratory crackles in both lung fields. An x-ray of the chest shows diffuse interstitial infiltrates bilaterally. A Gram stain of saline-induced sputum shows no organisms. Inoculation of the induced sputum on a cell-free medium that is enriched with yeast extract, horse serum, cholesterol, and penicillin G grows colonies that resemble fried eggs. Which of the following organisms was most likely isolated on the culture medium?
- A. Bordetella pertussis
- B. Haemophilus influenzae
- C. Cryptococcus neoformans
- D. Mycoplasma pneumoniae (Correct Answer)
- E. Coxiella burnetii
Chlamydia pneumoniae Explanation: ***Mycoplasma pneumoniae***
- The patient's presentation with **atypical pneumonia** symptoms (fatigue, headache, dry cough, diffuse interstitial infiltrates) along with the characteristic **"fried egg" colonies** cultured on a specialized medium (enriched with yeast extract, horse serum, cholesterol, and penicillin G) are highly indicative of *Mycoplasma pneumoniae*.
- Unlike most bacteria, *Mycoplasma pneumoniae* lacks a **cell wall**, explaining why it does not stain on Gram stain and requires specific culture conditions.
*Bordetella pertussis*
- This organism causes **whooping cough** and is characterized by distinct paroxysmal cough followed by an inspiratory 'whoop,' not typically the diffuse interstitial infiltrates and mild crackles described.
- *Bordetella pertussis* is usually cultured on **Bordet-Gengou agar** or Regan-Lowe medium, not the specialized medium described, and does not form "fried egg" colonies.
*Haemophilus influenzae*
- This bacterium is a common cause of **bacterial pneumonia** but typically presents with more acute symptoms and localized infiltrates, often seen in individuals with underlying lung disease or in children.
- *Haemophilus influenzae* would grow on standard chocolate agar and would not produce "fried egg" colonies; it also stains Gram-negative coccobacilli.
*Cryptococcus neoformans*
- This is a **fungus**, not a bacterium, and is a significant cause of pneumonia and meningoencephalitis, especially in immunocompromised individuals.
- Its presence would typically be identified by **India ink stain** (showing encapsulated yeast) or specific fungal cultures, not the described "fried egg" appearance on bacterial media.
*Coxiella burnetii*
- This intracellular bacterium causes **Q fever**, which can present with atypical pneumonia symptoms, but it is an **obligate intracellular parasite** and therefore cannot be grown on cell-free artificial media like the one described.
- Diagnosis typically relies on **serological tests** or PCR, as it cannot be easily cultured in a standard lab setup.
Chlamydia pneumoniae US Medical PG Question 10: A 27-year-old man comes to the physician with throbbing right scrotal pain for 1 day. He has also had a burning sensation on urination during the last 4 days. He is sexually active with multiple female partners and does not use condoms. Physical examination shows a tender, palpable swelling on the upper pole of the right testicle; lifting the testicle relieves the pain. A Gram stain of urethral secretions shows numerous polymorphonuclear leukocytes but no organisms. Which of the following is the most likely causal pathogen of this patient's symptoms?
- A. Mycobacterium tuberculosis
- B. Pseudomonas aeruginosa
- C. Mumps virus
- D. Chlamydia trachomatis (Correct Answer)
- E. Staphylococcus aureus
Chlamydia pneumoniae Explanation: ***Chlamydia trachomatis***
- The patient's presentation with **epididymitis** (scrotal pain, tender palpable swelling on the upper pole of the testicle), **dysuria**, and a history of **multiple sexual partners without condoms** is classic for a sexually transmitted infection.
- **Positive Prehn's sign** (pain relief with testicular elevation) supports epididymitis over testicular torsion.
- The Gram stain showing **numerous polymorphonuclear leukocytes but no organisms** is highly suggestive of *C. trachomatis* infection, as it is an **obligate intracellular bacterium** that does not readily stain with Gram stain.
- This finding distinguishes it from *Neisseria gonorrhoeae* (the other common cause of STI-related epididymitis in young men), which would appear as **Gram-negative intracellular diplococci**.
*Mycobacterium tuberculosis*
- **Tuberculosis epididymitis** is rare in developed countries and typically presents with a more **insidious onset** over weeks to months, not acute onset over 1 day.
- It may involve caseating granulomas and is more common in immunocompromised patients.
- It would not explain the acute dysuria or the Gram stain findings of PMNs without organisms in a patient with risk factors for common STIs.
*Pseudomonas aeruginosa*
- **Pseudomonas epididymitis** is typically seen in older men (>35 years), those with urinary tract abnormalities, or after instrumentation/catheterization.
- It is uncommon in young, sexually active individuals without these risk factors.
- Gram stain would show **Gram-negative rods**, which is inconsistent with the "no organisms" finding.
*Mumps virus*
- **Mumps orchitis** typically presents with **testicular pain and swelling** (affecting the testis itself, not the epididymis).
- Mumps orchitis is usually preceded by **parotitis** (salivary gland swelling) 4-8 days earlier.
- It does not typically cause dysuria or lead to urethral secretions with PMNs.
- Mumps is now rare due to widespread MMR vaccination.
*Staphylococcus aureus*
- **Staphylococcus aureus** can cause epididymitis, especially in cases of direct trauma, hematogenous spread, or in patients with indwelling catheters.
- However, it's not a common cause of sexually transmitted epididymitis in young, healthy men.
- A Gram stain would reveal **Gram-positive cocci in clusters**, which was not seen in this case.
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