Preponderance of vaccine-preventable diseases hotspots in northern Ghana: a spatial and space-time clustering analysis from 2010 to 2014

Abstract

Background: Vaccine-preventable diseases (VPDs) persist globally with a disproportionately high burden in Low and Middle-Income Countries (LMICs). Although this might be partly due to the failure to sustain vaccination coverage above 90% in some WHO regions, a more nuanced understanding of VPD transmission beyond vaccination coverage may unveil other important factors in VPD transmission and control. This study identified VPDs hotspots and explored their relationships with ecology, urbanicity and land-use variations (Artisanal and Small-scale Gold Mining (ASGM) activities) in Ghana.

Methods: District-level disease count data from 2010 to 2014 from the Ghana Health Service (GHS) and population data from the Ghana Population and Housing Census (PHC) were used to determine clustering patterns of six VPDs (Measles, Meningitis, Mumps, Otitis media, Pneumonia and Tetanus). Spatial and space-time cluster analyses were implemented in SaTScan using the discrete Poisson model. P-values were estimated using a combination of sequential Monte Carlo, standard Monte Carlo, and Gumbel approximations.

Results: The study found a preponderance for VPD hotspots in the northern parts of Ghana and northernmost ecological zones (Sudan Savannah and Guinea Savannah). Incidence of meningitis was higher in the Sudan Savannah ecological zone relative to: Tropical Rain Forest (p = 0.001); Semi Deciduous Forest (p < 0.0001); Transitional Zone (p < 0.0001); Coastal Savannah (p < 0.0001) and Guinea Savannah (p = 0.033). Except for mumps, which recorded a higher incidence in urban districts (p = 0.045), incidence of the other five VPDs did not differ across the urban-rural divide. Whereas spatial analysis suggested that some VPD hotspots (tetanus and otitis media) occur more frequently in mining districts in the southern part of the country, a Mann-Whitney U test revealed a higher incidence of meningitis in non-mining districts (p = 0.019). Pneumonia and meningitis recorded the highest (722.8 per 100,000) and least (0.8 per 100,000) incidence rates respectively during the study period.

Conclusion: This study shows a preponderance of VPD hotspots in the northern parts of Ghana and in semi-arid ecoclimates. The relationship between ASGM activities and VPD transmission in Ghana remains blurred and requires further studies with better spatial resolution to clarify.

Keywords: ASGM; Artisanal and Small-Scale Gold Mining; Ecological zones; Ghana; Hotspots; Immunization; VPD; Vaccine-preventable Diseases.

Fig. 1

Choropleths showing the incidence and clustering of measles in the study area (A) A choropleth of measles incidence in the study area (2010–2014); (B) Measles cluster map: this choropleth shows the top 5 most likely spatial measles cluster in the study area. Four (4) clusters (1,2,3 and 4) are hotspots (red) whiles a single cluster (5) is a cold spot (blue)

Fig. 2

Choropleths showing the incidence and clustering of meningitis in Ghana (A) A choropleth of meningitis incidence in the study area (2010–2014); (B) Meningitis cluster map: this choropleth shows the top 5 most likely spatial meningitis cluster in the study area. All five (5) clusters are hotspots (red)

Fig. 3

Choropleths showing the incidence and clustering of measles mumps in Ghana (A) A choropleth of mumps incidence in the study area (2010–2014); (B) Mumps cluster map: this choropleth shows the top 5 most likely spatial mumps cluster in the study area. All five (5) clusters are hotspots (red)

Fig. 4

Choropleths showing the incidence and clustering of otitis media in Ghana (A) Otitis media incidence map for Ghana (2010–2014): this choropleth shows otitis media incidence for each of the 170 districts in Ghana. (B) Otitis media cluster map: this choropleth shows the top 5 most likely otitis media clusters in the study area. Three of the clusters (1, 4 and 5) are hotspots (red) whiles two clusters (2 and 3) are cold spots (blue)

Fig. 5

Choropleths showing the incidence and clustering of pneumonia in Ghana (A) Pneumonia incidence map for Ghana (2010–2014): this choropleth shows pneumonia incidence for each of the 170 districts in Ghana. (B) Pneumonia cluster map: this choropleth shows the top 5 most likely pneumonia cluster in Ghana. Three of the clusters (1, 4 and 5) are hotspots (red) whiles two clusters (2 and 3) are cold spots (blue)

Fig. 6

Choropleths showing the incidence and clustering of tetanus in Ghana (A) Tetanus incidence map for Ghana (2010–2014): Tetanus incidence for each of the 170 districts in Ghana. (B) A choropleth showing the top 5 most likely tetanus clusters in Ghana. All 5 cluster had were hotspots (elevated) disease rates

Fig. 7

Most likely cluster of all six VPDs. Most likely cluster of the six VPDs included in this study. Areas coloured red are the most likely clusters and the area coloured pink is the where meningitis and pneumonia overlap. The green diamonds indicate districts with mining activities