Chlamydia trachomatis Genital Infection vs Gonorrhea

Why Azithromycin 1 g orally, taken as a single dose is correct

• She has uncomplicated chlamydial cervicitis in pregnancy (mucopurulent endocervical discharge, friable cervix, positive NAAT, and no fever, cervical motion tenderness, or adnexal tenderness to suggest PID); CDC 2021 names azithromycin 1 g orally in a single dose as the recommended regimen for chlamydia in pregnancy.
• Azithromycin is safe and effective throughout pregnancy, and the single dose can be taken in the clinic under direct observation, which removes the adherence problem of a 7-day course.
• The negative gonorrhea NAAT means azithromycin alone is sufficient; if gonorrhea were positive or not excluded, ceftriaxone 500 mg IM once (1 g if 150 kg or more) would be added.
• Treating before delivery prevents vertical transmission, which causes neonatal chlamydial conjunctivitis and afebrile infant pneumonia.

Why the others are wrong

• Levofloxacin 500 mg orally once daily for 7 days - Active against chlamydia and a CDC alternative for nonpregnant adults, but although human data suggest low fetal risk, animal studies raise concern for cartilage damage in neonates, and CDC 2021 lists only azithromycin (recommended) and amoxicillin (alternative) for chlamydia in pregnancy (the trap is swapping in the nonpregnant alternative once doxycycline is ruled out).
• Doxycycline 100 mg orally twice daily for 7 days - The preferred regimen outside pregnancy, but CDC lists doxycycline as contraindicated in the second and third trimesters because of the risk of fetal tooth discoloration, and at 18 weeks she is in the second trimester (the trap is applying the nonpregnant first-line regimen without checking pregnancy status).
• Metronidazole 2 g orally, taken as a single dose - Safe in pregnancy and a familiar single-dose STI regimen, but metronidazole has no useful activity against C. trachomatis, the organism the NAAT identified; even for trichomoniasis, CDC 2021 reserves the 2 g single dose for men and prefers metronidazole 500 mg twice daily for 7 days in women (the trap is choosing a convenient, pregnancy-safe single dose without checking that the drug covers the organism).

Additional high-yield points

• The CDC alternative in pregnancy is amoxicillin 500 mg orally three times daily for 7 days; erythromycin is no longer recommended because its gastrointestinal side effects lead to nonadherence.
• Pregnancy is the setting where a test of cure is recommended: repeat NAAT about 4 weeks after treatment, then retest 3 months after treatment. Nonpregnant patients treated with a recommended or alternative regimen need only the 3-month retest unless adherence is in doubt, symptoms persist, or reinfection is suspected.
• Screen all pregnant patients younger than 25 years, and older patients at increased risk, at the first prenatal visit, and rescreen the same groups in the third trimester; because she is younger than 25, she is rescreened in the third trimester whether or not she remains at risk.
• Sex partners from the preceding 60 days need evaluation and treatment (expedited partner therapy where permitted); she should abstain from sex for 7 days after the single dose and until partners are treated.
• Neonatal erythromycin eye prophylaxis is ineffective against chlamydial ophthalmia neonatorum and does not prevent infant pneumonia, so prenatal screening and treatment is the real prevention.

Why Disseminated gonococcal infection is correct

• The classic DGI arthritis-dermatitis syndrome is the triad of migratory asymmetric polyarthralgia/arthritis, tenosynovitis (especially wrists and fingers), and pustular skin lesions on the extremities, with fever.
• DGI characteristically strikes young, sexually active patients, and women are at higher risk around menses and during pregnancy, fitting this menstruating 24-year-old with a recent new partner.
• Joint fluid Gram stain and culture are frequently negative in the arthritis-dermatitis form because it is largely immune/bacteremic rather than purulent; diagnosis relies on NAAT or culture of genital and extragenital sites plus blood cultures.
• CDC 2021 treatment of DGI is ceftriaxone 1 g IV/IM daily for at least 7 days plus empiric chlamydia coverage; recurrent DGI should prompt evaluation for terminal complement deficiency (C5-C9, order CH50).

Why the others are wrong

• Reactive post-enteric arthritis is an asymmetric oligoarthritis with conjunctivitis and urethritis after a GU/GI infection (HLA-B27 associated); it does not produce pustular skin lesions with tenosynovitis and fever in this acute STI context.
• Staphylococcal septic arthritis is the most common bacterial monoarthritis, but it produces a single hot purulent joint with a frequently positive Gram stain, not migratory polyarthralgia, tenosynovitis, and pustular skin lesions.
• Polyarticular rheumatoid arthritis is a symmetric small-joint polyarthritis with morning stiffness developing over weeks to months; it does not present acutely with fever, pustular skin lesions, and a recent sexual-exposure history.