Which condition requires oral erythromycin treatment for conjunctivitis?

Chlamydial conjunctivitis is caused by the bacterium Chlamydia trachomatis and requires specific antibiotic treatment. Oral erythromycin is the preferred treatment for this condition, especially in newborns, as it is effective against Chlamydia and helps avoid complications such as pneumonia which can occur if the infection is not treated properly.

In cases of gonococcal conjunctivitis, the treatment typically involves parenteral antibiotics rather than oral medications, as this condition can progress quickly and pose serious risks. Allergic conjunctivitis is managed with antihistamines or topical steroids, not antibiotics, since it is an allergic response rather than a bacterial infection. Bacterial conjunctivitis can often be treated effectively with topical antibiotics, depending upon the causative organism, but oral erythromycin is not the first-line treatment for simple bacterial infections.

Thus, the necessity for systemic treatment with oral erythromycin specifically highlights the appropriate management of chlamydial conjunctivitis, making this the correct answer.