A 3year old boy presented with recurrent attacks of pneumonia and otitis media since 1st bihday. Diagnosis is X-linked agammaglobulinemia and most likely offending organism is

X-LINKED AGAMMAGLOBULINEMIAPatients with X-linked agammaglobulinemia (XLA), or Bruton agammaglobulinemia, have a profound defect in B-lymphocyte development resulting in severe hypogammaglobulinemia, an absence of circulating B cells, small to absent tonsils, and no palpable lymph nodes.Clinical ManifestationsMost boys afflicted with XLA remain well during the 1st 6-9 mo of life by viue of maternally transmitted IgG antibodies. Thereafter, they acquire infections with extracellular pyogenic organisms, such as Streptococcus pneumoniae and Haemophilus influenzae, unless they are given prophylactic antibiotics or immunoglobulin therapy. Infections include sinusitis, otitis media, pneumonia, or, less often, sepsis or meningitis. Infections with Mycoplasma are also paicularly problematic. Chronic fungal infections are seen; Pneumocystis jiroveci pneumonia rarely occurs. Viral infections are usually handled normally with the exceptions of hepatitis viruses and enterovirusesReference: Nelson Textbook of Paediatrics; 20th edition; Chapter 124; Primary Defects of Antibody Production