A 4-week-old girl presents with fever, cough, and increased work of breathing. Vital signs: rectal temperature 38.3°C (100.9°F); respiratory rate, 60/min; heart rate, 160/min. You hear coarse breath sounds and rhonchi. The abdomen is soft and the remainder of the examination is unremarkable. The WBC count is 18,000/mm3 and chest radiograph shows a dense air-space consolidation of the right lower lobe. The most common bacterial cause of pneumonia in this neonatal period is:
Group B Streptococcus.
+Streptococcus pneumoniae.
+Staphylococcus aureus.
+Haemophilus influenzae.
+Mycoplasma pneumoniae.
Bacterial causes of pneumonia in the neonatal age group are group B streptococci, Listeria monocytogenes, E. coli, and other gram-negative bacilli. Chlamydiatrachomatis and Ureaplasma urealyticum are important causes in infants younger than 16 weeks. Beyond the neonatal period, S. pneumoniae is the predominant bacterial pathogen in all age groups, although its incidence has been decreasing since the introduction of the heptavalent pneumococcal conjugate vaccine. H. influenzae has become a less common cause of pneumonia especially after the introduction of the HIB vaccine. S. aureus, M. pneumoniae, and Chlamydia pneumoniae are less frequent causes after S. pneumoniae. Viral causes of pneumonia in the neonate include Herpes simplex virus, CMV, and rubella. RSV and parainfluenza are the most common viral causes of pneumonia from 1 to 24 months of age. From 6 months to 5 years of age, influenza, Epstein-Barr virus (EBV), and adenovirus predominate.