Population-based incidence and serotype distribution of invasive pneumococcal disease prior to introduction of conjugate pneumococcal vaccine in Bangladesh.

Background: Bangladesh introduced the 10-valent pneumococcal conjugate vaccine (PCV-10) in 2015. We measured population-based incidence of invasive pneumococcal disease (IPD) prior to introduction of PCV-10 to provide a benchmark against which the impact of PCV-10 can be assessed.

Methods: We conducted population, facility and laboratory-based surveillance in children 0-59 months of age in three rural sub-districts of Sylhet district of Bangladesh from January 2014 to June 2015. All children received two-monthly home visits with one week recall for morbidity and care seeking. Children attending the three Upazilla Health Complexes (UHC, sub-district hospitals) in the surveillance area were screened for suspected IPD. Blood samples were collected from suspected IPD cases for culture and additionally, cerebrospinal fluid (CSF) was collected from suspected meningitis cases for culture and molecular testing. Pneumococcal isolates were serotyped by Quellung. Serotyping of cases detected by molecular testing was done by sequential multiplex polymerase chain reaction.

Results: Children under surveillance contributed to 126,657 child years of observations. Sixty-three thousand three hundred eighty-four illness episodes were assessed in the UHCs. Blood specimens were collected from 8,668 suspected IPD cases and CSF from 177 suspected meningitis cases. Streptococcus pneumoniae was isolated from 46 cases; 32 (70%) were vaccine serotype. The population-based incidence of IPD was 36.3/100,000 child years of observations. About 80% of the cases occurred in children below two years of age.

Discussion: IPD was common in rural Bangladesh suggesting the potential benefit of an effective vaccine. Measurement of the burden of IPD requires multiple surveillance modalities.