| Birth to 20 days | Bacteria | Bacteria |
| | Escherichia coli | | Anaerobic organisms |
| | Group B streptococci | | Group D streptococci |
| | Listeria monocytogenes | | Haemophilus influenzae |
| | | | Streptococcus pneumoniae |
| | | | Ureaplasma urealyticum |
| | | Viruses |
| | | | Cytomegalovirus |
| | | | Herpes simplex virus |
| 3 weeks to 3 months | Bacteria | Bacteria |
| | Chlamydia trachomatis | | Bordetella pertussis |
| | S. pneumoniae | | H. influenzae type B and nontypeable |
| Viruses | | Moraxella catarrhalis |
| | Adenovirus | | Staphylococcus aureus |
| | Influenza virus | | U. urealyticum |
| | Parainfluenza virus 1, 2, and 3 | Virus |
| | Respiratory syncytial virus | | Cytomegalovirus |
| 4 months to 5 years | Bacteria | Bacteria |
| | Chlamydia pneumoniae | | H. influenzae type B |
| | Mycoplasma pneumoniae | | M. catarrhalis |
| | S. pneumoniae | | Mycobacterium tuberculosis |
| Viruses | | Neisseria meningitis |
| | Adenovirus | | S. aureus |
| | Influenza virus | Virus |
| | Parainfluenza virus | | Varicella-zoster virus |
| | Rhinovirus | |
| | Respiratory syncytial virus | |
| 5 years to adolescence | Bacteria | | Bacteria |
| | C. pneumoniae | | H. influenzae |
| | M. pneumoniae | | Legionella species |
| | S. pneumoniae | | M. tuberculosis |
| | | | S. aureus |
| | | Viruses |
| | | | Adenovirus |
| | | | Epstein-Barr virus |
| | | | Influenza virus |
| | | | Parainfluenza virus |
| | | | Rhinovirus |
| | | | Respiratory syncytial virus |
| | | | Varicella-zoster virus |