Van Mens et al investigated the contribution of S. pneumoniae in CAP by measuring serologic responses in patients who were hospitalized due to CAP in the Ovidius and Triple P study, two consecutive clinical trials initiated by the St Antonius Hospital Nieuwegein. This analysis showed a much higher proportion of patients with pneumococcal pneumonia than was diagnosed by conventional methods alone (i.e. blood cultures, sputum cultures or urine antigen tests). Interestingly some patients with a culture proven pneumococcal pneumonia did not show a serotype specific antibody response to the infecting serotype.(4) Possibly these patients had a temporarily low titre due to the infection but another explanation is that there might be a structurally impaired immune response against S. pneumoniae or certain serotypes.