Invasive pneumococcal disease.

INTRODUCTION Streptococcus pneumoniae, the pneumococcus, is a Gram-positive diplococcus with more than 90 serotypes determined by the polysaccharide composition of its capsule. It is carried asymptomatically in approximately 50% of people.1 It can cause both non-invasive and invasive disease. Invasive pneumococcal disease (IPD) refers to disease in which the bacterium enters a sterile site such as blood, cerebrospinal fl uid (CSF), pleural fl uid, joint fl uid or pericardial fl uid. Non-invasive disease includes otitis media, sinusitis and bronchitis. Among infectious diseases, IPD is a leading cause of morbidity and mortality in children and adults. Vaccination against pneumococcal infection was introduced into the UK routine childhood immunisation programme in 2006 with Prevenar 7 (Pfi zer, Tadworth, UK), a sevenvalent conjugate vaccine, replaced in 2010 with the 13-valent vaccine Prevenar 13. Pneumococcal disease continues to be a problem despite these measures.