The leading cause of ophthalmia neonatorum in the United States is which organism?

• A. Chlamydia trachomatis
• B. Neisseria gonorrhoeae
• C. Staphylococcus aureus
• D. Herpes simplex virus

Answer: (A)

Neonatal conjunctivitis acquired during delivery is most often caused by Chlamydia trachomatis in the United States. This organism is transmitted from mother to baby as the infant passes through the birth canal, leading to a delayed-onset conjunctivitis that typically appears about 5–14 days after birth. The presentation is usually mucopurulent discharge with follicular inflammation, rather than the severe, sudden purulent discharge associated with Neisseria gonorrhoeae infection. Prophylaxis at birth has reduced gonococcal ophthalmia neonatorum, so Chlamydia remains the more common culprit. In contrast, gonococcal infection tends to present earlier (within a few days) and with more aggressive purulence and higher risk of corneal involvement; herpes simplex virus conjunctivitis often shows dendritic corneal ulcers and can involve skin lesions; Staphylococcus aureus can cause conjunctivitis but is not the leading cause in newborns.