Invasive pneumococcal infections in Vellore, India: clinical characteristics and distribution of serotypes

Streptococcus pneumoniae infection is a serious problem worldwide and the case fatality rate remains high. The aim of this study was to analyze the distribution of pneumococcal serotypes causing invasive pneumococcal disease (IPD), to survey the potential coverage of present and future vaccines, and to investigate differences between serotypes and groups of serotypes with regard to manifestation, case fatality rate, age, and other risk factors.

Isolates from 244 consecutive patients with IPD were collected at the Christian Medical College, Vellore, India between January 2007 and June 2011, and clinical data were obtained retrospectively. Clinical characteristics were analyzed both for individual serotypes and for those grouped as "invasive", "pediatric", or "vaccine" serotypes.

The serotype coverage for the pneumococcal conjugated vaccines (PCV) PCV7, PCV10, PCV13, PCV15, and pneumococcal polysaccharide vaccine (PPV) PPV23 was 29%, 53%, 64%, 66%, and 73%, respectively. The proportion of IPD caused by vaccine types was lower than pre-vaccination studies from other parts of the world. In adults, serotype 1 was mainly isolated from previously healthy patients without risk factors for IPD. This serotype caused more pneumonia and less meningitis than other serotypes, as was also noted for the "invasive" serotypes (1, 5, and 7 F).

The most common pneumococcal serotypes in this study behaved in similar ways to those in countries where the PCV has been introduced. Also, the most common serotypes in this study are included in the new PCVs. Therefore, a national program of childhood immunization with PCV10/13 in India is likely to be successful.