American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the typical causative organism of bacterial conjunctivitis?

1. Staphylococcus aureus

2. Streptococcus pneumoniae

3. Escherichia coli

4. Haemophilus influenzae

The correct answer is: Staphylococcus aureus

The typical causative organism of bacterial conjunctivitis is often Staphylococcus aureus, which is known for its ability to cause a variety of infections, including skin and soft tissue infections. It is a gram-positive bacterium that can be transmitted easily, especially in settings where close contact occurs, such as schools and daycare centers. In the context of conjunctivitis, Staphylococcus aureus can cause symptoms such as redness, discharge, and irritation in the eye, leading to inflammation of the conjunctiva. Moreover, it can be especially problematic due to antibiotic resistance seen in some strains, which complicates treatment and requires careful consideration when prescribing antibiotics. While other organisms such as Streptococcus pneumoniae and Haemophilus influenzae can also lead to conjunctivitis, they are less commonly associated with this condition compared to Staphylococcus aureus in various populations. Escherichia coli primarily causes gastrointestinal infections and is not typically a causative agent of conjunctivitis, making Staphylococcus aureus the most relevant answer in this context.