[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Immunology](https://durgical.com/en/immunology/) › [Immunodeficiencies](https://durgical.com/en/immunology/#a-immunodeficiency) › Immunodeficiency: warning signs and the infection pattern by defect

[Immunology](https://durgical.com/en/immunology/) · [Immunodeficiencies](https://durgical.com/en/immunology/#a-immunodeficiency)

# Immunodeficiency: warning signs and the infection pattern by defect

- Topic

When infections come too often, last too long or are caused by unusual germs, the immune system may be missing a piece.

Updated 2026-11-01

## Key points

- Antibody (B-cell) defects: encapsulated bacteria in the sinuses and lungs, usually after maternal antibodies fade around 6 months of age.
- T-cell and combined defects: viruses, fungi (Candida, Pneumocystis) and intracellular germs from the first months, with failure to thrive and chronic diarrhea.
- Phagocyte defects: skin and organ abscesses, catalase-positive bacteria and Aspergillus, poor pus formation or delayed wound healing.
- Terminal complement (C5–C9) defects: recurrent Neisseria infections; early classical pathway defects (C1q, C2, C4): lupus-like disease.
- Start simple: complete blood count with differential, serum IgG, IgA and IgM, vaccine antibody titers and an HIV test; then lymphocyte subsets, oxidative burst or CH50 as the pattern suggests.

## What it is

An immunodeficiency is a reduced or absent immune response. Primary (inborn) defects are rare and usually show up in childhood; secondary (acquired) ones from HIV, malnutrition, drugs or loss of the spleen are far more common. The kind of germ that keeps causing trouble points to the part of the immune system that fails, and that guides the first tests.

## Key facts

- Warning signs in children: several ear or sinus infections in one year, two or more pneumonias in a year, antibiotics for months with little effect, deep abscesses, persistent thrush, needing IV antibiotics, poor growth and a family history of immunodeficiency.
- Warning signs in adults: repeated ear, sinus or lung infections, chronic diarrhea with weight loss, recurrent viral infections (herpes, warts), deep abscesses, persistent fungal infections and infection with atypical mycobacteria.
- Two or more warning signs justify an evaluation by an immunologist (Jeffrey Modell Foundation criteria).
- A severe infection from a germ that rarely harms healthy people (an opportunistic infection) is itself a clue.
- Live vaccines (BCG, rotavirus, oral polio, MMR, varicella, yellow fever) can cause disease in severe T-cell defects; a BCG complication in an infant is a classic SCID clue.

## The infection pattern by defect

| Defect | Usual onset | Typical germs and clues | First tests |
| --- | --- | --- | --- |
| Antibody (B cell) | After about 6 months (maternal IgG fades); CVID in adults | Encapsulated bacteria (pneumococcus, Haemophilus), sinusitis, otitis, pneumonia, Giardia, enteroviruses | IgG, IgA, IgM; vaccine titers; CD19 B-cell count |
| T cell / combined | First weeks to months of life | Candida, Pneumocystis, CMV and other viruses, chronic diarrhea, failure to thrive, live-vaccine disease | Lymphocyte count; CD3, CD4, CD8 by flow cytometry; TREC newborn screen |
| Phagocyte | Infancy or childhood | Staphylococcus aureus, Aspergillus, Serratia, Nocardia; abscesses, poor pus, gingivitis | Neutrophil count; DHR oxidative burst test; CD18 by flow cytometry |
| Complement | Any age | Neisseria (terminal C5–C9); encapsulated bacteria (C3); lupus-like disease (C1q, C2, C4) | CH50 (classical), AH50 (alternative), C3, C4 |
| [Secondary (acquired)](https://durgical.com/en/conditions/hiv-infection-and-aids/) | Any age, often adults | Depends on cause: opportunistic infections in HIV, encapsulated bacteria after splenectomy | HIV test, glucose, albumin, drug history, smear for Howell-Jolly bodies |

## Clinical notes

- Recurrent infections that all occur in one site (for example, one lung lobe) suggest an anatomic problem such as a foreign body or bronchiectasis, not an immunodeficiency.
- In Colombia and Latin America, secondary causes (HIV, malnutrition, steroids, chemotherapy) are far more frequent than inborn errors, but inborn errors are underdiagnosed.
- Infants with suspected severe T-cell deficiency should not receive live vaccines or non-irradiated blood products until the evaluation is complete.

## Memory aid

Ask what kind of germ keeps winning: capsules point to antibodies, fungi and viruses to T cells, abscesses to phagocytes, Neisseria to complement.

## Test yourself

Think of the answer, then tap the question to see it.

## Why do children with X-linked agammaglobulinemia usually stay well for the first months of life?

Maternal IgG crosses the placenta and protects them until it fades, around 6 months of age; then recurrent bacterial infections begin.

## A child has recurrent skin abscesses and a liver abscess due to Staphylococcus aureus. Which part of the immune system is suspected?

Phagocytes (neutrophils), for example chronic granulomatous disease; an oxidative burst test (DHR) is the screening test.

## Recurrent meningococcal infections point to a deficiency of which complement components?

The terminal components C5 to C9 (the membrane attack complex), screened with the CH50.

## What does an infant with chronic diarrhea, thrush, failure to thrive and Pneumocystis pneumonia suggest?

A severe T-cell or combined immunodeficiency such as SCID.

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## Related

- [B-cell (antibody) deficiencies: XLA, CVID, IgA deficiency, hyper-IgM](https://durgical.com/en/immunology/b-cell-deficiencies-xla-cvid-iga-deficiency-hyper-igm/)
- [T-cell and combined deficiencies: DiGeorge, SCID, Wiskott–Aldrich, ataxia-telangiectasia](https://durgical.com/en/immunology/t-cell-and-combined-deficiencies-digeorge-scid-wiskott-aldrich-ataxia-telangiect/)
- [Phagocyte defects: CGD, LAD, Chédiak–Higashi](https://durgical.com/en/immunology/phagocyte-defects-cgd-lad-chediak-higashi/)
- [Complement deficiencies and hereditary angioedema](https://durgical.com/en/immunology/complement-deficiencies-and-hereditary-angioedema/)
- [Secondary immunodeficiency: HIV, malnutrition, drugs, asplenia](https://durgical.com/en/immunology/secondary-immunodeficiency-hiv-malnutrition-drugs-asplenia/)
- [The neutropenic and immunosuppressed patient (nursing)](https://durgical.com/en/immunology/the-neutropenic-and-immunosuppressed-patient/)

## Related conditions

- [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/)
- [Adenosine deaminase deficiency (ADA-SCID)](https://durgical.com/en/conditions/adenosine-deaminase-deficiency/)

## Microorganisms

- [Streptococcus pneumoniae](https://durgical.com/en/microbiology/streptococcus-pneumoniae/)
- [Haemophilus influenzae](https://durgical.com/en/microbiology/haemophilus-influenzae/)
- [Pneumocystis jirovecii](https://durgical.com/en/microbiology/pneumocystis-jirovecii/)
- [Candida albicans](https://durgical.com/en/microbiology/candida-albicans/)
- [Aspergillus fumigatus](https://durgical.com/en/microbiology/aspergillus-fumigatus/)
- [Staphylococcus aureus](https://durgical.com/en/microbiology/staphylococcus-aureus/)
- [Neisseria meningitidis](https://durgical.com/en/microbiology/neisseria-meningitidis/)
- [Giardia duodenalis](https://durgical.com/en/microbiology/giardia-duodenalis/)

[← All of immunology](https://durgical.com/en/immunology/)

Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.

Sources: [10 Warning Signs of PI](https://www.info4pi.org/information-booth/10-warning-signs/) (Jeffrey Modell Foundation, 2026); [Immunodeficiency diseases](https://medlineplus.gov/ency/article/000818.htm) (MedlinePlus, U.S. National Library of Medicine, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/immunology/immunodeficiency-warning-signs-and-the-infection-pattern-by-defect/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/immunology/immunodeficiency-warning-signs-and-the-infection-pattern-by-defect/