American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the most common cause of bacterial conjunctivitis in adults?

1. Streptococcus pneumoniae

2. Neisseria gonorrhoeae

3. Staphylococcus aureus

4. Haemophilus influenzae

The correct answer is: Neisseria gonorrhoeae

In the context of bacterial conjunctivitis in adults, the most common causative organism is indeed Staphylococcus aureus. This bacterium frequently colonizes the conjunctival sac and skin, making it a prevalent pathogen responsible for this condition. While Neisseria gonorrhoeae is a known cause of conjunctivitis, particularly in sexually active individuals and newborns, it is less common in the general adult population compared to Staphylococcus aureus. Other bacteria like Streptococcus pneumoniae and Haemophilus influenzae can also lead to conjunctivitis, but their incidence in adults is not as high as that of Staphylococcus aureus, which is the primary culprit in most cases of bacterial conjunctivitis in the adult demographic. Understanding the prevalence of these organisms helps in guiding appropriate empirical treatment for bacterial conjunctivitis, emphasizing the importance of Staphylococcus aureus as the most common cause.