| Pathogen | Associated clinical syndromes and/or clinical features | |
| Bacteria | Streptococcus pneumoniae (pneumococcus) | Pneumonia, bacteremia, and meningitis. Purpura fulminans may be more common in asplenic patients. |
| Haemophilus influenzae | Pneumonia, bacteremia, and meningitis. | |
| Neisseria meningitidis (meningococcus) | Bacteremia, meningitis. Rash may accompany bacteremia and/or meningitis and may be petechial or purpuric. | |
| Capnocytophaga species | Zoonotic illness typically acquired from a dog bite resulting in cellulitis, bacteremia, meningitis, purpura fulminans, and/or gangrene. | |
| Bordetella holmesii | Pertussis (whooping cough), bacteremia, cellulitis, septic arthritis, pericarditis, and endocarditis. Incidence may be higher during pertussis outbreaks. | |
| Parasites | Babesia species | Tickborne or transfusion-transmitted illness characterized by fever, headache, arthralgias, and hemolytic anemia. Most common in coastal New England. |
| Plasmodium falciparum | Fever in a patient who has recently travelled to or lives in a malaria-endemic region (eg, most tropical regions of the world, especially sub-Saharan Africa). | |
