Geospatial Distribution of Invasive Pneumococcal Disease and Radiologically Confirmed Pneumonia in Rural Communities in Gambia
Background Pneumonia is a respiratory disease that affects millions of people around the world, the majority of which live in developing countries. While a significant proportion of childhood pneumonia has been reduced with modern medicine, pneumonia remains the leading cause of death for children under five. In Gambia, the introduction of a 13-valent pneumococcal conjugate vaccine sparked fears of replacement carriage of Streptococcus pneumoniae in children, and a surveillance system was set up to monitor the effectiveness of the vaccine, as well as its effects on the population. Methods The surveillance system collected data on Invasive Pneumococcal Disease (IPD) and Radiologically Confirmed Pneumonia (RCP) in the Upper River Region of the Gambia for a period of several years (2007-ongoing), in addition to demographic and geographic data. Cases of IPD and RCP were mapped in a GIS and then analysed using statistical scanning software to identify any patterns through space or time to determine any spatio-temporal differences. Additionally, a new adaptive kernel smoothing method was used to produce risk surfaces, allowing diseases to be directly compared. Results IPD and RCP showed differing mapping characteristics across some basic demographic information (age grouping, vaccination status, and ethnicity). Vaccine type serotypes differed from non-vaccine types, with PCV-13 coverage appearing to protect against its target serotypes. Overall significant clustering of IPD “spread” outwards from the original baseline cluster to surrounding regions, while RCP clusters move eastwards after the baseline period, and cover a much wider area, indicating greatly increased rates. Slight variations occur between age groupings, representing the higher burden of IPD at a younger age, while RCP affects slightly older children. Hotspots of vaccine type serotypes were identified, as well as non-vaccine type, indicating areas of interest for improved vaccination coverage. Significant differences in geospatial distribution of cases occur for both IPD and RCP during Before and After time periods of the vaccination program, as evidenced by the shift in clustering across the map. Incidence rates show peaks in IPD in 2010 (82/100,000), but show an overall decrease over time, while RCP shows the highest peak in 2012 (521/100,000), with an increasing trend over time. Conclusion The impact of pneumococcal conjugate vaccines is having a noticeable effect on IPD and RCP cases across time and age groups. The differing characteristics of the diseases showed initial geographic similarities at baseline, which have diverged as the time period goes on. Clusters are expanding and shifting locations for both diseases, while hotspots of disease continue to pop up throughout different time periods. The overall reduction in IPD cases indicates intermediate success for the PCV-13 program, while the hotspots of both vaccine and non-vaccine type serotypes indicate areas to focus on moving forward.
Advisor: Hill, Philip; MacKenzie, Grant; Touray, Kebba
Degree Name: Master of Public Health
Degree Discipline: Preventive and Social Medicine
Publisher: University of Otago
Keywords: pneumonia; spatial analysis; distribution; invasive pneumococcal disease; clustering; pneumococcal conjugate vaccine; vaccine surveillance
Research Type: Thesis