| Infection | Clinical features |
| Common causes | |
| Epstein-Barr virus (EBV)* | Infectious mononucleosis (fever, exudative pharyngitis, hepatosplenomegaly); positive monospot or EBV serology |
| Cytomegalovirus (CMV)* | Mononucleosis-like illness; positive CMV serology |
| Uncommon causes | |
| Human immunodeficiency virus (HIV)* | High-risk behavior (unprotected sexual contact, injection drug use, etc) |
| Toxoplasmosis* | Exposure to cat feces; ingestion of poorly cooked meat, soil, or contaminated food; posterior cervical involvement |
| Mycobacterium tuberculosis* | Birth in, travel to, or contact with a visitor from a region endemic for Mycobacterium tuberculosis; tuberculin skin test usually with ≥15 mm induration at 48 hours; positive interferon-gamma release assay |
| Mycobacterium bovis | Ingestion of unpasteurized dairy products; exposure to cattle |
| Syphilis* | High-risk sexual behavior |
| Rare causes | |
| Brucellosis* | Travel to or living in endemic area; ingestion of unpasteurized dairy products |
| Histoplasmosis* | Associated skin lesions |
