Streptococcus pneumoniae antibody titres in patients with primary antibody deficiency receiving intravenous immunoglobulin (IVIG) compared to subcutaneous immunoglobulin (SCIG).

Intravenous immunoglobulin (IVIG) and subcutaneous immunoglobulin (SCIG) are effective in the treatment of patients with primary antibody deficiency disorders (PAD). The purpose of this study was to evaluate Streptococcus pneumoniae (Spn) antibody titres to 14 serotypes in patients receiving IVIG compared to SCIG and to correlate Spn antibody levels to clinical outcome. The doses of immunoglobulin (Ig)G/kg/month were similar in both IVIG and SCIG groups. In 11 patients treated with IVIG, Spn antibody titres were ≥ 1·3 μg/ml to 99·4 ± 2·1% of the 14 serotypes at peak IVIG but decreased to 66·9 ± 19·8% at trough IVIG. Loss of Spn titres ≥ 1·3 μg/ml was most frequent for Spn serotypes 1, 4, 9V and 23. This correlated with lower Spn antibody titres to these serotypes at peak IVIG compared to the other serotypes. In 13 patients treated with SCIG, Spn antibody titres were protective to 58·2 ± 23·3% of the serotypes 3-5 days after infusion, similar to trough IVIG. Similarly, the Spn serotypes with the least protective percentages were the same as the ones observed in trough IVIG. There were no annualized serious bacterial infections (aSBI) in either group. However, there were significantly decreased annualized other infections (aOI) in the SCIG group compared to the IVIG-treated group, 0·8 ± 0·7 versus 2·2 ± 1·2 infections/patient/year (P = 0·004). Breakthrough aOI did not correlate with protective or higher serum Spn antibody titres.