Recognising Immunodeficiency in Children
On this page
Direct answer
Recurrent, deep, unusual or persistent infections — four pneumonias in a year, two deep abscesses, persistent oral thrush beyond infancy, disseminated BCG in an infant — should raise immunodeficiency above "just low immunity"; the Jeffrey Modell ten warning signs are the screening checklist. Secondary immunodeficiency (malnutrition, measles, HIV, steroids) outnumbers primary disease many times over in India, but primary disorders have a teachable logic by age and organism: antibody defects declare after maternal IgG wanes at four to six months with sinopulmonary and diarrhoeal infections; combined T-cell defects (SCID) present in the first months with opportunists — Pneumocystis, persistent candida, chronic diarrhoea, failure to thrive — and are killed by live vaccines; complement defects recur with Neisseria. A lymphocyte count low for age on an existing CBC is the free clue to SCID, a paediatric emergency.
What you must remember
- The 10 warning signs (Jeffrey Modell): eight or more ear infections yearly, two or more serious sinusitis, two or more months of ineffective antibiotics, two or more pneumonias a year, failure to thrive with infection, recurrent deep abscesses, persistent thrush after one year, intravenous-antibiotic need, two or more deep-seated infections, and family history.
- Age-of-onset logic: opportunists and oral thrush from birth — combined T-cell (SCID); four to six months onwards with sinopulmonary infection — antibody deficiency (maternal IgG gone); later childhood to adolescence — common variable immunodeficiency, complement or specific antibody defects.
- Bruton agammaglobulinaemia (X-linked): boys after about six months, recurrent bacterial infection, absent tonsils and adenoids, absent B cells (CD19) with all immunoglobulin classes low; replacement immunoglobulin 400-600 mg/kg every three to four weeks.
- SCID: the emergency — chronic diarrhoea, Pneumocystis pneumonia, persistent candida, failure to thrive, lymphopenia for age, absent thymic shadow; live vaccines (BCG, OPV, rotavirus, measles) cause disseminated disease; management is cotrimoxazole prophylaxis, immunoglobulin, irradiated CMV-negative blood and stem-cell transplantation; ADA deficiency is the classic enzymatic type.
- Syndromic patterns: DiGeorge (22q11.2): CATCH-22 — cardiac defects, abnormal facies, thymic aplasia, cleft palate, hypocalcaemia — suspect in a neonate with hypocalcaemic convulsions and conotruncal heart disease. Wiskott-Aldrich: eczema, small-platelet thrombocytopenia and recurrent pyogenic infection in a boy.
- Organism-specific defects: chronic granulomatous disease — recurrent abscesses and granulomas with catalase-positive organisms (Staphylococcus aureus, Aspergillus, Serratia, Nocardia) including BCGitis, diagnosed by an absent nitroblue tetrazolium (or DHR) test; terminal complement (C5-C9) deficiency — recurrent meningococcal disease.
- Workup ladder: CBC with differential (lymphopenia or neutropenia for age), immunoglobulins, post-vaccination titres, lymphocyte subsets, HIV serology always, then targeted function tests (NBT, DHR, complement) with genetic confirmation.
A seven-month-old who keeps failing
A seven-month-old of consanguineous parents has been admitted thrice: Pneumocystis pneumonia, oral candida resisting topical therapy, chronic diarrhoea with weight faltering — and the BCG scar is inflamed and draining. The assembly is diagnostic before any fancy test: opportunists plus persistent candida plus failure to thrive plus disseminated BCG in an infant means combined immunodeficiency. Notice the free clue — the old CBC shows a lymphocyte count of 1600, low for a seven-month-old (infants normally run 4000 or more). Act as an emergency: isolate, stop all live vaccines, start cotrimoxazole prophylaxis, replace immunoglobulin, use irradiated CMV-negative blood, and refer urgently for transplantation — survival falls with every infection accumulated while waiting. The counter-case: a toddler with six ear infections a year, normal growth and vaccine responses, has daycare exposure, not immunodeficiency.
Where students slip
Sending every SCID stem to an HIV test alone is the classic miss — HIV is on the list, but BCGitis plus candida in an infant is combined immunodeficiency until proven otherwise, and consanguinity nudges toward primary disease. Second: in Bruton the tonsils are absent and CD19 counts near zero — a physical-sign-plus-lab pairing the exam loves. Third: organism specificities — catalase-positive organisms for CGD, Neisseria for complement, enterovirus and giardia for antibody defects, Pneumocystis and candida for T-cell defects. Fourth: an otherwise well child with anaphylactoid transfusion reactions needs IgA levels, not an allergy label.
Frequently asked questions
What are the Jeffrey Modell warning signs of primary immunodeficiency?
Eight-plus ear infections yearly, two-plus serious sinusitis, ineffective two-month antibiotic courses, two-plus pneumonias a year, failure to thrive with infection, deep abscesses, persistent thrush after one year, intravenous-antibiotic need, deep-seated infections, and family history.
Which immunodeficiency presents in early infancy with opportunistic infection?
Severe combined immunodeficiency — Pneumocystis, persistent candida, chronic diarrhoea, failure to thrive, lymphopenia for age, absent thymic shadow — a transplant-track emergency in which live vaccines are lethal.
Why does Bruton agammaglobulinaemia present after six months of age?
Passively transferred maternal IgG protects until it degrades over the first months of life; once gone, the boy with no B cells and near-absent tonsils develops recurrent bacterial sinopulmonary infection.
Which organisms suggest chronic granulomatous disease?
Catalase-positive organisms — Staphylococcus aureus, Aspergillus, Serratia, Nocardia — including BCGitis, diagnosed by an absent nitroblue tetrazolium reduction.
What screening tests start the immunodeficiency workup?
Complete blood count with differential for age-appropriate lymphocyte and neutrophil counts, quantitative immunoglobulins, post-vaccination antibody titres and HIV testing, escalating to lymphocyte subsets and functional assays.