Introduction Specific Antibody Deficiency (SAD) is associated with recurrent childhood lower respiratory tract infections (LRTI). SAD in children as a clinical entity is poorly defined, and has been described as a primary immunodeficiency of unknown origin. SAD can be identified by measuring antibodies to childhood vaccines, and a failure to respond to booster immunisations. The prevalence of SAD and its clinical significance in children is poorly understood.
Objectives The aim of this study is to determine the extent of SAD in children followed with recurrent respiratory tract infections at a tertiary paediatric respiratory centre.
Methods All patients with recurrent LRTI's attending our complex paediatric respiratory clinic over a 12-month period were studied. Results of specific antibody levels to pneumococcus and the response to booster vaccines were reviewed.
Results 102 children with recurrent respiratory infections were seen during this period (age range 10 months to 18 years, median age 4 years 10 months). Sixty-four children had specific IgG antibody levels to pneumococcus vaccine serotypes tested, of which 45 (70%) had low antibody levels. Of these, 27 patients received either Prevenar (a polysaccharide conjugated vaccine containing seven serotypes) or Pneumovax II booster vaccines (a polysaccharide vaccine containing 23 pneumococcal serotypes), and were subsequently retested for their specific IgG antibody levels. Adequate levels of antibodies tested post-booster were mounted in only 13 patients (48%).
Conclusions The prevalence of SAD in children with troublesome recurrent LRTI's is high and may be under-diagnosed. Pneumococcal vaccine booster response is variable in these children. The clinical significance of SAD and the response to booster immunisation warrants further study.