Table 1.

Type of immune defect according to disease/treatment and range of commonly associated pathogens

Immune disorder	Causes	Typical microorganisms
Neutrophil disorders
Neutropenia	Drugs (chemotherapy, azathioprine, methotrexate, carbimazole, sulphonamides) Leukaemia AIDS Felty's syndrome Aplastic anaemia Early HSCT	Gram-positive bacilli (Staphylococcus aureus, streptococci) Gram-negative bacilli Fungi (Aspergillus spp., Candida spp., non-Aspergillus filamentous fungi)
Neutrophil chemotaxis	Diabetes mellitus Cirrhosis Sarcoidosis Drugs (glucocorticoids, amphotericin B)	Staph. aureus Streptococci Candida spp. Zygomycosis
Neutrophil phagocytosis	Chronic granulomatous disease Myeloproliferative disorders Inherited phagocyte defects	Staph. aureus Nocardia spp. Gram-negative bacilli Fungi (Aspergillus spp., Candida spp., non-Aspergillus filamentous fungi)
T-cell-mediated immunity	AIDS Lymphoma HSCT Solid organ transplantation Drugs (T-cell-depleting antibodies, glucocorticoids, ciclosporin, tacrolimus)	Herpesviruses, Respiratory viruses Pneumocystis jirovecii Endemic mycoses, e.g. Histoplasma capsulatum, Cryptococcus Parasites (Strongyloides, Toxoplasma) Mycobacteria Nocardia Legionella pneumophila
B-cell-mediated/antibody deficiency	Multiple myeloma Plasmapheresis Drugs (anti-B-cell therapies) HSCT Chronic lymphocytic leukaemia Lymphoma Multiple myeloma	Encapsulated bacteria (e.g. Streptococcus pneumoniae, Haemophilus influenzae) Herpesviruses
Other
Complement deficiency	Congenital Acquired (systemic lupus erythematosus, anorexia nervosa)	Encapsulated bacteria (e.g. Strep. pneumoniae, Haem. influenzae) Staph. aureus
Asplenia	Splenectomy Sickle cell disease	Encapsulated bacteria (e.g. Strep. pneumoniae, Haem. influenzae) Staph. aureus

HSCT, haemopoietic stem cell transplantation.