2025 – PAGE 306 – INFECTIOUS DISEASES

(DOUBLE TAKE) CHLAMYDIA TRACHOMATIS

Chlamydia trachomatis can cause urethritis, conjunctivitis and pelvic inflammatory disease (PID). In neonates, it can cause pneumonia associated with a staccato cough. PID can lead to ectopic pregnancies and infertility. Eye infections can lead to blindness. Conjunctivitis in a neonate (less than a month old) should raise concern for this as the etiology (vertical transmission). It’s an obligate intracellular anaerobe. Getting cultures is difficult, so order PCR of CELLS, secretions, or urine. Chlamydia can also cause lymphogranuloma venereum (LGV), which is an STD that initially starts with small, nontender papules or shallow ulcers that resolve. Then a TENDER UNILATERAL INGUINAL lymph node appears that can rupture, relieve the pain, and then possibly drain for months.

• ­SEXUALLY TRANSMITTED DISEASE (STD): Treat with DOXYCYCLINE for 7 days. If the patient is given doxycycline and there is treatment failure, a recurrence, a concern for noncompliance, or a doxycycline allergy, then treat with a single dose of AZITHROMYCIN or treat with LEVOFLOXACIN for 7 days. Test for other STDs including gonorrhea, syphilis, and HIV and treat if positive.
• ­CONJUNCTIVITIS: Treat with oral erythromycin to eradicate nasopharyngeal colonization, which can lead to pneumonia.
• ­(DOUBLE TAKE) LYMPHOGRANULOMA VENEREUM SEROVAR is an STD caused by Chlamydia trachomatis. It is rare in the U.S. but more common in tropical areas. It starts as small nontender papules or shallow ulcers that resolve. Eventually, a TENDER UNILATERAL INGUINAL lymph node appears. Pain is relieved when it ruptures. The node can continue to drain for months. Treat with DOXYCYCLINE or erythromycin.
• PEARL: In general, when you think the diagnosis is due to a Chlamydia species, choose doxycycline or a macrolide (usually erythromycin). Also, this is an intracellular organism. Look for the phrase “intracytoplasmic inclusions.”
• PEARL: While chlamydia is often said to be the most common STD, that’s not the case. It’s the most common BACTERIAL STD, and it’s the most commonly REPORTED STD. HPV is the most common STD.

CHLAMYDIA PNEUMONIAE

Chlamydia pneumoniae causes an atypical pneumonia. It is often noted in school-age children who are 5-15 years of age. The patient may have tachypnea, a staccato cough ± eye discharge. For the boards, the patient may be AFEBRILE. Look for intracytoplasmic inclusion bodies and a gram-negative organism. You can also do a PCR. First-line therapy for children of all ages is a macrolide (erythromycin or azithromycin). Doxycycline or a fluoroquinolone would be acceptable, but as a second-line treatment.

PEARL: If you see the phrase “staccato cough,” PICK THIS!

PEARL: Both erythromycin and azithromycin are associated with increased risk of infantile hypertrophic pyloric stenosis (IHPS), particularly in infants younger than two weeks of age. But, the benefits outweigh the risks in this case. In this case, pick azithromycin when the baby is less than 6 weeks old.

CHLAMYDIA PSITTACI

Bird exposure + atypical pneumonia could represent a Chlamydia psittaci pneumonia on the exam. Treat with doxycycline or macrolides.