Infectious and immunological characteristics
| Clinical clues |
| Persistent infections despite standard treatment |
| Recurrent infections |
| Severe infections, including invasive infections such as meningitis, septic arthritis |
| Infections with opportunistic pathogens |
| Graft vs host disease either from maternally acquired lymphocytes or nonirradiated transfusions |
| Absent thymic shadow on chest x-ray |
| Family history of immunodeficiency or infant deaths from infection |
| Infectious agents |
| Bacteria, including Gram positive, Gram negative |
| Fungi |
| Viruses |
| Rotavirus and other intestinal viruses |
| Respiratory syncytial virus and other respiratory viruses |
| Cytomegalovirus and other herpesviruses |
| Opportunistic agents, such as Pneumocystis and disseminated bacillus Calmette-Guerin (BCG) (in countries using neonatal BCG vaccination) |
| Immunologic abnormalities |
| T cell lymphopenia < 2200 (compared with age-matched control values—healthy infants have higher lymphocyte counts than older individuals) |
| Poor responses to T-cell mitogens and antigens |
| Absent or nonfunctional B cells |
| Falling immunoglobulin (Ig) G (with waning maternal transplacental antibodies) and very low levels of IgA, IgM |
| Absent antibody responses to specific antigens, such as tetanus toxoid |
| Clinical clues |
| Persistent infections despite standard treatment |
| Recurrent infections |
| Severe infections, including invasive infections such as meningitis, septic arthritis |
| Infections with opportunistic pathogens |
| Graft vs host disease either from maternally acquired lymphocytes or nonirradiated transfusions |
| Absent thymic shadow on chest x-ray |
| Family history of immunodeficiency or infant deaths from infection |
| Infectious agents |
| Bacteria, including Gram positive, Gram negative |
| Fungi |
| Viruses |
| Rotavirus and other intestinal viruses |
| Respiratory syncytial virus and other respiratory viruses |
| Cytomegalovirus and other herpesviruses |
| Opportunistic agents, such as Pneumocystis and disseminated bacillus Calmette-Guerin (BCG) (in countries using neonatal BCG vaccination) |
| Immunologic abnormalities |
| T cell lymphopenia < 2200 (compared with age-matched control values—healthy infants have higher lymphocyte counts than older individuals) |
| Poor responses to T-cell mitogens and antigens |
| Absent or nonfunctional B cells |
| Falling immunoglobulin (Ig) G (with waning maternal transplacental antibodies) and very low levels of IgA, IgM |
| Absent antibody responses to specific antigens, such as tetanus toxoid |