A 2-week-old female presents with cough, conjunctivitis, nasal congestion, and an infiltrate on CXR. What is the most likely etiologic agent?

In this clinical scenario, the presence of cough, conjunctivitis, nasal congestion, and an infiltrate seen on chest X-ray in a 2-week-old infant suggests a specific infectious cause. Chlamydia trachomatis is a well-known cause of conjunctivitis in neonates and can lead to pneumonia, particularly in infants who exhibit respiratory symptoms alongside ocular manifestations.

In this age group, Chlamydia pneumoniae often presents with these symptoms due to its association with maternal infection during delivery. The connection between conjunctivitis and respiratory symptoms supports the diagnosis, as these infections can manifest simultaneously. The infiltrate on the chest X-ray further highlights the presence of pneumonia in the context of chlamydial infection.

Other potential causes like Streptococcus pneumoniae, Respiratory syncytial virus (RSV), or Haemophilus influenzae are less likely in this scenario. Streptococcus pneumoniae typically does not present with conjunctivitis alongside respiratory symptoms at this age. RSV is more common in younger infants but tends to present with different clinical features and is less associated with conjunctivitis. Similarly, Haemophilus influenzae is less common in neonates due to widespread vaccination and does not frequently cause conjunctivitis as a co-symptom.