Risk factors of infection include antibiotic pressure, foreign device, or underlying immune defects.

There is evidence of both an associated humoral and cellular immune defect in Whipple's disease, but no uniform abnormality has been shown.

Other contributing factors include exposure to carcinogens (cigarette smoke for lung cancer), or living for years with subtle immune defects.

Identification of genes defining the immune defects may identify new target genes for therapeutic approaches.

The nature of the infections, as well as the additional features, may provide clues as to the exact nature of the immune defect.

CVID is shown to be a genetically determined primary immune defect; however, the underlying causes are different.

It is possible that environmental agents or a virus provoke the immune defect, due to genetic predisposition, but this has not been clarified.

Dr. Laurence said that none of the patients showed a significant immune defect, although tests might not have detected some kinds of immune defects.

The other group of problems are specific manifestations of immune defects caused by HIV infection.

However, such infections only occur in people with a severe -immune defect, a serious disease affecting their hormones, or some other fundamental disorder.