Chlamydia trachomatis — MCQs

10 questions

A 22-year-old sexually active, otherwise healthy female presents to her primary care physician complaining of several days of dysuria, frequency, urgency, and suprapubic pain. She denies fever, flank pain, vaginal itching, or vaginal bleeding/discharge. Which organism is most likely responsible for this patient's symptoms?

A 35-year-old woman visits the office with complaints of yellowish vaginal discharge and increased urinary frequency for a week. She also complains of pain during urination. Past medical history is irrelevant. She admits to having multiple sexual partners in the past few months. Physical examination is within normal limits except for lower abdominal tenderness. Urine culture yields Chlamydia trachomatis. What is the most appropriate next step in the management of this patient?

A previously healthy 25-year-old man comes to the physician because of a 1-week history of fever and fluid release from painful lumps in his right groin. He had an atraumatic ulceration of his penis about 1 month ago that was not painful and resolved on its own within 1 week. He works at an animal shelter for abandoned pets. He is sexually active with multiple male partners and does not use condoms. His temperature is 38.5°C (101.3°F). Examination of the groin shows numerous tender nodules with purulent discharge. The remainder of the examination shows no abnormalities. Which of the following is the most likely causal pathogen?

A 22-year-old man comes to the physician because of an ulcer on his penis for 12 days. The ulcer is painful and draining yellow purulent material. He returned from a study abroad trip to India 3 months ago. His immunizations are up-to-date. He is sexually active with one female partner and uses condoms inconsistently. He appears uncomfortable. His temperature is 37.2°C (99.0°F), pulse is 94/min, and blood pressure is 120/80 mm Hg. Examination shows tender inguinal lymphadenopathy. There is a 2-cm ulcer with a necrotic base proximal to the glans of the penis. Which of the following is the most likely causal organism?

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 5-year-old girl is brought to the physician because of watery discharge from her right eye for 2 weeks. She and her parents, who are refugees from Sudan, arrived in Texas a month ago. Her immunization status is not known. She is at the 25th percentile for weight and the 50th percentile for height. Her temperature is 37.2°C (99°F), pulse is 90/min, and respirations are 18/min. Examination of the right eye shows matting of the eyelashes. Everting the right eyelid shows hyperemia, follicles, and papillae on the upper tarsal conjunctiva. Slit-lamp examination of the right eye shows follicles in the limbic region and the bulbar conjunctiva. There is corneal haziness with neovascularization at the 12 o'clock position. Examination of the left eye is unremarkable. Direct ophthalmoscopy of both eyes shows no abnormalities. Right pre-auricular lymphadenopathy is present. Which of the following is the most likely diagnosis in this patient?

A 31-year-old woman presents to her gynecologist for a routine well-visit. She is sexually active with multiple male partners and uses an intrauterine device for contraception. Her last menstrual period was two weeks ago. She denies abnormal vaginal discharge or sensations of burning or itching. Pelvic exam is normal. Routine Pap smear shows the following (see Image A). Which organism is most likely responsible for her abnormal Pap smear?

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 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?

Q10

A 32-year-old man comes to the physician because of low-grade fever and progressive painful lumps in his right groin for 6 days. The lumps have been discharging purulent fluid since the evening of the previous day. He had a shallow, painless lesion on his penis 3 weeks ago, but was too embarrassed to seek medical attention; it has resolved in the meantime. There is no personal or family history of serious illness. He has smoked one pack of cigarettes daily for 12 years. He is sexually active with multiple male partners and uses condoms inconsistently. His temperature is 38.0°C (100.4°F). Examination of his groin shows multiple masses discharging pus. The remainder of the examination shows no abnormalities. Which of the following is the most likely causal organism?

Chlamydia trachomatis US Medical PG Practice Questions and MCQs

Question 1: A 22-year-old sexually active, otherwise healthy female presents to her primary care physician complaining of several days of dysuria, frequency, urgency, and suprapubic pain. She denies fever, flank pain, vaginal itching, or vaginal bleeding/discharge. Which organism is most likely responsible for this patient's symptoms?

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

Explanation: ***Escherichia coli*** - **_E. coli_** is the most common cause of **uncomplicated urinary tract infections (UTIs)**, accounting for 75-95% of cases. - The patient's symptoms of **dysuria, frequency, urgency**, and **suprapubic pain** are classic for cystitis, a common manifestation of _E. coli_ infection. *Chlamydia trachomatis* - While _Chlamydia_ can cause **urethritis** with dysuria, it is often associated with vaginal discharge/bleeding and is primarily a sexually transmitted infection. - The absence of **vaginal symptoms** makes it less likely to be the primary cause of these specific urinary symptoms in this scenario. *Proteus mirabilis* - **_Proteus mirabilis_** is a common cause of UTIs, particularly those associated with **struvite stones** due to its urease activity. - While it can cause similar symptoms, it is less common than _E. coli_ in uncomplicated cystitis and often seen in complicated UTIs or those with a history of recurrent infections. *Staphylococcus saprophyticus* - _Staphylococcus saprophyticus_ is a common cause of UTIs in sexually active young women, but it is typically the **second most common** after _E. coli_. - While a possibility, **_E. coli_ remains the most likely** given its high prevalence in uncomplicated cystitis. *Klebsiella pneumoniae* - _Klebsiella pneumoniae_ is more commonly associated with **hospital-acquired UTIs**, complicated UTIs, or infections in patients with underlying medical conditions, such as diabetes. - It is a much less common cause of **uncomplicated community-acquired cystitis** in healthy young women compared to _E. coli_.

Question 2: A 35-year-old woman visits the office with complaints of yellowish vaginal discharge and increased urinary frequency for a week. She also complains of pain during urination. Past medical history is irrelevant. She admits to having multiple sexual partners in the past few months. Physical examination is within normal limits except for lower abdominal tenderness. Urine culture yields Chlamydia trachomatis. What is the most appropriate next step in the management of this patient?

A. Acyclovir
B. Doxycycline (Correct Answer)
C. Metronidazole
D. Clindamycin
E. Boric acid

Explanation: ***Doxycycline*** - **Doxycycline** is a recommended first-line treatment for **Chlamydia trachomatis** infections (along with azithromycin). - A 7-day course of **doxycycline 100 mg orally twice daily** is highly effective in eradicating the infection. - **Alternative:** Azithromycin 1 g PO single dose is also first-line and may be preferred for compliance. *Acyclovir* - **Acyclovir** is an antiviral medication used to treat **herpes simplex virus (HSV)** infections. - It is ineffective against **bacterial infections** like Chlamydia. *Metronidazole* - **Metronidazole** is an antibiotic primarily used for **anaerobic bacterial** and **parasitic infections** (e.g., bacterial vaginosis, trichomoniasis). - It is not effective against **Chlamydia trachomatis**. *Clindamycin* - **Clindamycin** is an antibiotic effective against a range of **bacterial infections**, including some anaerobic bacteria. - However, it is not a recommended treatment for **Chlamydia trachomatis** infections. *Boric acid* - **Boric acid** is an antifungal agent primarily used for treating **recurrent vulvovaginal candidiasis** (yeast infections). - It has no role in treating **bacterial infections** like Chlamydia.

Question 3: A previously healthy 25-year-old man comes to the physician because of a 1-week history of fever and fluid release from painful lumps in his right groin. He had an atraumatic ulceration of his penis about 1 month ago that was not painful and resolved on its own within 1 week. He works at an animal shelter for abandoned pets. He is sexually active with multiple male partners and does not use condoms. His temperature is 38.5°C (101.3°F). Examination of the groin shows numerous tender nodules with purulent discharge. The remainder of the examination shows no abnormalities. Which of the following is the most likely causal pathogen?

A. Haemophilus ducreyi
B. Klebsiella granulomatis
C. Treponema pallidum
D. Bartonella henselae
E. Chlamydia trachomatis (Correct Answer)

Explanation: ***Chlamydia trachomatis*** - The presentation of a **painless penile ulcer** followed by **painful inguinal lymphadenopathy** (buboes) with **purulent discharge** is classic for **lymphogranuloma venereum (LGV)**, caused by specific serovars (L1, L2, L3) of **Chlamydia trachomatis**. - **Sexual activity with multiple male partners** and **lack of condom use** are risk factors for sexually transmitted infections, including LGV. *Haemophilus ducreyi* - This pathogen causes **chancroid**, which typically presents with **multiple, painful genital ulcers** and often painful inguinal lymphadenopathy, but the initial ulcer described here was painless. - The initial lesion in chancroid is usually soft and ragged, distinguishing it from the firm, painless chancre of syphilis. *Klebsiella granulomatis* - This bacterium causes **granuloma inguinale (donovanosis)**, characterized by **painless, progressively enlarging ulcerative lesions** in the anogenital area that are highly vascular and bleed easily. - It does not typically present with the dramatic inguinal lymphadenopathy and purulent discharge seen in LGV, although pseudobuboes can occur. *Treponema pallidum* - This spirochete causes **syphilis**. The primary lesion of syphilis is a **painless chancre**, similar to the initial penile ulcer described. - However, the subsequent **inguinal lymphadenopathy** in primary syphilis is typically **non-tender, bilateral**, and firm, unlike the painful, suppurative nodes observed here. *Bartonella henselae* - This bacterium is the causative agent of **cat scratch disease**, which typically presents with a **papule or pustule at the site of a cat scratch** followed by regional lymphadenopathy. - The patient's job at an animal shelter might suggest exposure, but the presentation of a penile ulcer followed by suppurative inguinal lymphadenitis is not characteristic of cat scratch disease.

Question 4: A 22-year-old man comes to the physician because of an ulcer on his penis for 12 days. The ulcer is painful and draining yellow purulent material. He returned from a study abroad trip to India 3 months ago. His immunizations are up-to-date. He is sexually active with one female partner and uses condoms inconsistently. He appears uncomfortable. His temperature is 37.2°C (99.0°F), pulse is 94/min, and blood pressure is 120/80 mm Hg. Examination shows tender inguinal lymphadenopathy. There is a 2-cm ulcer with a necrotic base proximal to the glans of the penis. Which of the following is the most likely causal organism?

A. Klebsiella granulomatis
B. Haemophilus ducreyi (Correct Answer)
C. Herpes simplex virus 2
D. Treponema pallidum
E. Chlamydia trachomatis

Explanation: ***Haemophilus ducreyi*** - The presentation of a **single, painful penile ulcer** with a **necrotic base** and **tender inguinal lymphadenopathy** is classic for **chancroid**, - This condition is caused by **Haemophilus ducreyi**, and the patient's recent travel to India, where chancroid is endemic, increases the likelihood of this diagnosis. *Klebsiella granulomatis* - This bacterium causes **granuloma inguinale (donovanosis)**, which typically presents with **painless, beefy-red ulcers** that bleed easily, - The ulcer described in the patient is **painful** and has a **necrotic base**, which is inconsistent with donovanosis. *Herpes simplex virus 2* - **Herpes simplex virus (HSV-2)** typically causes **multiple, painful vesicular lesions** that rupture to form shallow ulcers, often accompanied by systemic symptoms like fever and malaise. - The patient describes a **single, large ulcer** with a necrotic base, which is not characteristic of herpetic lesions. *Treponema pallidum* - **Treponema pallidum** causes **syphilis**, which presents as a **painless chancre** with a clean base and firm, non-tender lymphadenopathy in its primary stage. - The patient's ulcer is explicitly described as **painful** and draining **purulent material**, ruling out a syphilitic chancre. *Chlamydia trachomatis* - Certain serovars of **Chlamydia trachomatis** cause **lymphogranuloma venereum (LGV)**, which initially presents as a transient, **painless papule or ulcer** that often goes unnoticed, followed by significant, painful inguinal lymphadenopathy (buboes). - While LGV involves painful lymphadenopathy, the initial ulcer is typically small and unnoticed, and the described ulcer is large, painful, and has a necrotic base, which is not characteristic of LGV.

Question 5: 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

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.

Question 6: A 5-year-old girl is brought to the physician because of watery discharge from her right eye for 2 weeks. She and her parents, who are refugees from Sudan, arrived in Texas a month ago. Her immunization status is not known. She is at the 25th percentile for weight and the 50th percentile for height. Her temperature is 37.2°C (99°F), pulse is 90/min, and respirations are 18/min. Examination of the right eye shows matting of the eyelashes. Everting the right eyelid shows hyperemia, follicles, and papillae on the upper tarsal conjunctiva. Slit-lamp examination of the right eye shows follicles in the limbic region and the bulbar conjunctiva. There is corneal haziness with neovascularization at the 12 o'clock position. Examination of the left eye is unremarkable. Direct ophthalmoscopy of both eyes shows no abnormalities. Right pre-auricular lymphadenopathy is present. Which of the following is the most likely diagnosis in this patient?

A. Neisserial conjunctivitis
B. Trachoma conjunctivitis (Correct Answer)
C. Acute herpetic conjunctivitis
D. Angular conjunctivitis
E. Acute hemorrhagic conjunctivitis

Explanation: ***Trachoma conjunctivitis*** - The constellation of **follicles and papillae on the upper tarsal conjunctiva**, **limbal follicles**, **corneal haziness with neovascularization (pannus)**, and **pre-auricular lymphadenopathy** in a child from an endemic region (Sudan) is classic for **trachoma**. - This chronic form of conjunctivitis is caused by *Chlamydia trachomatis* serovars A, B, and C, leading to progressive scarring that can eventually cause **trichiasis** and blindness. *Neisserial conjunctivitis* - This condition typically presents with **hyperacute onset**, **copious purulent discharge**, and significant eyelid swelling, often within days of birth or infection. - While it can cause corneal involvement, the chronic follicular and papillary changes with limbal follicles and pannus are not characteristic. *Acute herpetic conjunctivitis* - Usually presents with **unilateral follicular conjunctivitis**, often accompanied by **periorbital vesicles** or a history of cold sores. - While it can cause corneal involvement (typically **dendritic ulcers**), the specific follicular changes, presence of papillae, and chronic course leading to pannus seen here are not typical. *Angular conjunctivitis* - Characterized by **redness, excoriation, and maceration** primarily localized to the **outer canthus** (angle) of the eye, often caused by *Moraxella lacunata* or *Staphylococcus aureus*. - It does not present with the diffuse follicular and papillary changes, limbal follicles, or corneal neovascularization described in this patient. *Acute hemorrhagic conjunctivitis* - This is typically an **acute, highly contagious viral conjunctivitis** characterized by **subconjunctival hemorrhages**, rapid onset, and usually resolves spontaneously. - It does not cause chronic follicular changes, limbal follicles, or corneal neovascularization, and the duration in this patient (2 weeks) suggests a more chronic process.

Question 7: A 31-year-old woman presents to her gynecologist for a routine well-visit. She is sexually active with multiple male partners and uses an intrauterine device for contraception. Her last menstrual period was two weeks ago. She denies abnormal vaginal discharge or sensations of burning or itching. Pelvic exam is normal. Routine Pap smear shows the following (see Image A). Which organism is most likely responsible for her abnormal Pap smear?

A. Trichomonas vaginalis
B. Human papillomavirus (Correct Answer)
C. Herpes simplex virus 1
D. Treponema pallidum
E. Chlamydia trachomatis

Explanation: **Human papillomavirus** - The image illustrates **koilocytes**, which are squamous epithelial cells with perinuclear halos and enlarged, hyperchromatic, and often irregular nuclei. These are pathognomonic for **human papillomavirus (HPV) infection**. - HPV is a sexually transmitted infection, and the patient's history of being **sexually active with multiple partners** increases her risk of exposure to HPV. *Trichomonas vaginalis* - *Trichomonas vaginalis* typically causes a **foamy, green-yellow vaginal discharge** and can lead to a "strawberry cervix" on speculum exam, neither of which are mentioned or depicted. - Pap smears infected with *Trichomonas* often show flagellated organisms and an inflammatory response, but not the characteristic koilocytes. *Herpes simplex virus 1* - Herpes simplex virus (HSV) infection on a Pap smear would typically show **multinucleated giant cells** with nuclear molding and intranuclear inclusions, not koilocytes. - Patients often present with painful genital lesions, which are absent in this case. *Treponema pallidum* - *Treponema pallidum* (syphilis) is a bacterial infection that would not be diagnosed via Pap smear cytology and does not cause koilocytes. - Primary syphilis presents as a **painless chancre**, while secondary syphilis involves a rash and systemic symptoms. *Chlamydia trachomatis* - *Chlamydia trachomatis* is a bacterial infection that can cause cervicitis, but it does not lead to koilocytic changes on a Pap smear. - Diagnosis relies on **nucleic acid amplification tests (NAATs)**, and symptoms, if present, might include abnormal discharge or post-coital bleeding.

Question 8: 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.

Question 9: 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 10: A 32-year-old man comes to the physician because of low-grade fever and progressive painful lumps in his right groin for 6 days. The lumps have been discharging purulent fluid since the evening of the previous day. He had a shallow, painless lesion on his penis 3 weeks ago, but was too embarrassed to seek medical attention; it has resolved in the meantime. There is no personal or family history of serious illness. He has smoked one pack of cigarettes daily for 12 years. He is sexually active with multiple male partners and uses condoms inconsistently. His temperature is 38.0°C (100.4°F). Examination of his groin shows multiple masses discharging pus. The remainder of the examination shows no abnormalities. Which of the following is the most likely causal organism?

A. Herpes simplex virus 2
B. Klebsiella granulomatis
C. Chlamydia trachomatis (Correct Answer)
D. Yersinia pestis
E. Haemophilus ducreyi

Explanation: ***Chlamydia trachomatis*** - The presentation of **painless genital ulcers** followed by painful inguinal lymphadenopathy that progresses to **suppurative buboes** (lumps discharging purulent fluid) is classic for **lymphogranuloma venereum (LGV)**, which is caused by specific serovars of *Chlamydia trachomatis* (L1, L2, L3). - The patient's history of multiple male partners and inconsistent condom use puts him at high risk for acquiring sexually transmitted infections like LGV. *Herpes simplex virus 2* - HSV-2 typically causes **painful, vesicular lesions** that can lead to recurrent outbreaks, which is inconsistent with the initial painless penile lesion described. - While HSV can cause lymphadenopathy, it usually presents as **tender, non-suppurative lymph nodes** rather than large, discharging buboes. *Klebsiella granulomatis* - This organism causes **donovanosis (granuloma inguinale)**, characterized by progressive, painless, beefy red **ulcerative lesions** that bleed easily. - It typically does not involve regional lymphadenopathy or bubo formation, but rather **pseudobuboes** formed by subcutaneous granulomas. *Yersinia pestis* - *Yersinia pestis* is the causative agent of **plague**, a severe systemic illness spread by fleas or respiratory droplets. - While plague can cause **buboes** (swollen, painful lymph nodes), it is associated with a much more acute and severe systemic illness, including high fever, prostration, and often hemorrhagic manifestations, which are not described here. *Haemophilus ducreyi* - This bacterium causes **chancroid**, which presents with **painful, friable genital ulcers** with ragged borders and often associated with tender inguinal lymphadenopathy that can suppurate. - The initial lesion described in the patient was **painless**, which rules out chancroid.

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