Descriptive Statistics
The statistical summary of malaria prevalence over the period 2014 - 2019 is presented in Table 1. According to the Table, malaria prevalence among children below the age of five years ranged from 2743/100,000 population to 12,916/100,000 with an average rate of 5952/100,000 individuals. The standard deviation of malaria prevalence (δ = 2261.92) which measures the degree of dispersion of cases from the mean, shows that there is wide variation in the prevalence rate of malaria under five years.
Table 1: Descriptive statistics of malaria prevalence among under-five years old
Mean
|
Minimum
|
Maximum
|
Std. Deviation
|
5952
|
2743
|
12,916
|
2261.92
|
Source: JSMoH, 2020 and Author’s analysis, 2021
The mean annual prevalence rate among those under-five years (5,952 per 100,000 or 5.95%) observed in this study is higher than 1.8% and 1.92% reported by Dawaki et al. (2016) and Solomon et al. (2020) respectively. However, our result (5.95%) is close to that of Alemu et al. (2012) and Nanvyat et al. (2017) who found 7.8% and 7.4% in Kola Diba, North Gondar, Ethiopia, and Jos Plateau State, Nigeria. In contrast, other studies have reported a high prevalence of 27.7% by Elechi et al. (2015) in Maiduguri, Borno State, Nigeria; 61.7% by West and Okari (2018) in Port Harcourt, Nigeria and 63% by Simon-Oke et al. (2019) in Ekiti State, Nigeria. Similarly, other high prevalence rates were reported in Africa and Asia. They include: 11.97% in Tanzania (Paul and Msengwa, 2018), 22.1% in Ghana (Yankson et al. {2019}), 22.1% in Ethiopia (Abossie et al. {2020}), 37.4% in Malawi (Gaston and Ramroop, 2020), 35.4% in Malawi (Chilanga et al. {2020}) and 42.3% in Indonesia (Jiero and Pasaribu, 2021). This variation in the results might be due to differences in climatic conditions, altitudinal variations, type of the study design employed, variations in the methods of malaria detection, differences in the coverage of intervention activities, and other factors that affect transmission.
The low prevalence rate among under-five children reported in this study might be related to increased awareness of the inhabitant of the state on the use of ITNs. This finding is not surprising considering the 2018 Nigeria Health Demography Survey Report, which revealed that household ownership of ITNs in the country is highest in Jigawa (the study area) and Kebbi States (98%) which is above the national target (NPC and ICF International, 2019). The report further disclosed that in Jigawa State, 90.5% of the surveyed children who are below five years of age slept under ITNs the night before the survey. This shows that the vast majority of the younger children are well protected from the infective bites by mosquitoes.
Spatial Patterns of Malaria Prevalence
Global spatial statistics using the Moran’s I measure were used to test for the significant pattern in the prevalence of malaria among under-five children in the study area. The test results (Table 2) showed overall positive and statistically significant Moran’s I (Moran’s I = 0.358122, Z score = 3.721018. P = 0.000198), suggesting a significant concentration of high prevalence rates (clustering). The result in Table 2 further shows a similar level of autocorrelation for the years under study. The clustering was strongest in the year 2018 (Moran’s I = 0.406459, Z score = 4.023251. P = 0.000057) followed by 2019 (Moran’s I = 0.310412, Z score = 3.263420, P = 0.001101).
Table 2: Spatial pattern of malaria prevalence
Years
|
Moran’s Index
|
Z-score
|
P value
|
Pattern
|
Under-five years:
|
|
|
|
|
2014
|
0.235427
|
2.614904
|
0.008925
|
Clustered
|
2015
|
0.214774
|
2.461729
|
0.013827
|
Clustered
|
2016
|
0.237812
|
2.501937
|
0.012352
|
Clustered
|
2017
|
0.287145
|
2.914179
|
0.003566
|
Clustered
|
2018
|
0.406459
|
4.023251
|
0.000057
|
Clustered
|
2019
|
0.310412
|
3.263420
|
0.001101
|
Clustered
|
2014-2019
|
0.358122
|
3.721018
|
0.000198
|
Clustered
|
Source: Author’s computation (2021)
The presence of significant positive autocorrelation for the years under study shows the extent to which neighbouring rates are correlated. Thus, LGAs sharing a border is more similar with respect to malaria than those that are distantly apart. However, the occurrence of malaria prevalence in these years in specific areas is not by chance. The statistically established spatial dependency of the disease implies the presence of similar risk factors in neighbouring areas thereby influencing the spatial transmission of the disease. This finding is not surprising since malaria is an environmental disease, and environmental variables are spatially related. Other similar studies (Sexena et al. 2012; Osayomi, 2014; Osei and Yibile, 2015; Yakudima and Adamu, 2019; Bizimana and Nduwayezu, 2020) had also revealed spatial clustering of malaria cases in their studies. However, these global test results indicate a need for further investigation using local spatial statistics (hotspot analysis).
Hotspot Analysis of Malaria for Children Under Five Years
Local spatial statistics using Getis-Ord Gi* was applied to detect the locations of clusters over the study periods. Figure 2 represents the result of the cumulative (2014 – 2019) hotspot analysis for the under-five years population group. The figure showed central and north-western parts of the state as the hotspot regions. Hotspots of 90% and 95% confidence levels were noted in the following LGAs: Kiyawa, Jahun, Dutse, Gwiwa, Roni, Kazaure, and Yan-kwashi. North-eastern part of the state (comprising Kaugama, Auyo, Hadejia, Malam Madori, Kiri Kasamma, Guri, and Birniwa LGAs) on the other hand formed the cold spot region.
The year-wise hotspot analysis results (figure 3a) showed a hotspot cluster at all three confidence levels in 2014. LGAs like Gwiwa, Roni, Yan-kwashi, Kazaure, and Kiyawa LGA formed the hotspot clusters. In 2015, only three LGAs (Jahun, Gwiwa, and Roni) showed hotspots at 95% and 90% confidence levels (figure 3b). For the remaining years of the study (2016-2019) four LGAs exhibit hotspot clusters (figures 3c-3f). Gwiwa, Roni, and Kiyawa LGAs appear as hotspot areas at 99% confidence level for two years of the analysis, while four LGAs including Birnin Kudu, Buji, Kazaure, and Yan-kwashi appear in the group (99% C.I.) in only one year. For 95% confidence level Dutse LGA consistently appears for the three years of the analysis, Jahun LGA appears in two years while Yan-kwashi, Kazaure, and Kiyawa each appeared in only one year. Six LGAs formed hotspot clusters at 90% confidence level, they are Kiyawa, Gwiwa, Roni, Jahun, Ringim, and Birnin Kudu, and each appeared in only one year.
On the other hand, the overall result (2014-2019) of hotspot analysis established a cold spot cluster in the north-eastern part of the state with Guri, Birniwa, and Kiri Kasamma at 99% confidence interval, while Kaugama, Malam Madori, and Hadejia fall under 95% confidence level (figure 2). Auyo LGA belongs to the cold spot at 90% confidence interval (figure 2). The yearly results show that Birniwa LGA consistently emerges as a significant cold spot (99%) for five consecutive years, Kiri Kasamma appears in three years, Malam Madori and Hadejia two years each, while Guri and Kaugama each appeared in only one year (figure 3a-3f). At 95% confidence level Guri LGA occurs under a cold spot for five years, Kiri Kasamma and Kaugama (3 years), Malam Madori (2 years), while Hadejia, Auyo, and Birniwa had emerged in only one year.
Identification of a hotspot cluster consistently located in the central and the north-western parts of the state was the most significant outcome of cluster analysis. A possible explanation for the consistent clustering of malaria in these areas could be the presence of favourable conditions for malaria transmission. Some LGAs like Jahun and Kiyawa shared borders with other LGAs that have wetlands where traditional rice cultivation is practiced. Rice fields according to Gurthmann et al. (2002) are the most favourable sites for the mosquito to breed. In addition, most of the LGAs that fall within and surrounding the clusters have water streams that allow for the cultivation of vegetables and other crops. These water agro-systems may provide significant habitat for mosquito breeding and thus, increase the vector population for malaria transmission. This finding is confirmed by the works of Rulisa et al. (2013) and Bizimana & Nduwayezu (2020) that discovered significant malaria hotspots located close to water-based agro-ecosystems.
The second likely factor is urbanization. Jigawa State is made up of five emirate districts. The headquarters of these districts are considered the major towns in the state and are therefore providing employment opportunities and other services, hence attracting people from other areas. Three out of the five emirate headquarters were part of the identified clusters. Osayomi (2014) established an association between malaria and urbanization in Nigeria. This association was due to the fact that most towns are characterized by poor sanitary conditions, such as improper disposal of waste, poor condition of drainage, and an unclean housing environment among others. All these encourage the breeding of mosquitoes and thus, promote the transmission of malaria.
The availability of formal healthcare centres in these 11 LGAs may partly explain the emergence of hotspot clusters in the areas. This finding was supported by a study on the distribution of healthcare facilities in Jigawa state by Yakudima (2018) who found that nearly 60% of modern health facilities in the state are concentrated in these areas. Another likely reason for a stable hotspot in these areas is that the existing malaria control and intervention measures might have not been taken correctly or might have not been applied appropriately.
Our analysis further showed that the coldspots are majorly concentrated in the north-eastern part of the state. This area is characterized by low rainfall and high temperature. Adequate rainfall is required to recharge existing water bodies or create new ones which serve as breeding sites. The low rainfall receives in this area makes mosquito breeding habitats so scarce thus, low transmission intensity of malaria. Temperature is also considered a key determinant of transmission. This area (north-east) is associated with high temperatures for most of the year. The high temperature at 40oc reduces mosquito abundance due to the long larval duration (Dale et al. {2005}). Low rainfall coupled with high temperature affects the development of vegetation cover in the area. Adequate vegetation cover provides favourable conditions for malaria vectors to rest. The sparse nature of vegetation cover in the area can reduce mosquito density. All these factors could partly explain the low transmission of malaria in the area leading to cold spot conditions.
Table 3 summarized the number of LGAs identified as hotspots and coldspots for each year. From the table, the number of LGAs reported as hotspots cluster across the state was highest in the year 2014 and slightly lower during the 2016-2019 periods.
Table 3: Number of LGAs per type and intensity of malaria cluster
Confidence Interval
|
2014
|
2015
|
2016
|
2017
|
2018
|
2019
|
2014-2019
|
Under-five years:
|
|
|
|
|
|
|
|
Coldspots 99% C.I.
|
1
|
3
|
1
|
1
|
5
|
3
|
3
|
Coldspots 95% C.I.
|
2
|
-
|
5
|
4
|
2
|
3
|
3
|
Coldspots 90% C.I.
|
-
|
-
|
1
|
1
|
1
|
1
|
1
|
Not significant
|
19
|
21
|
16
|
17
|
15
|
16
|
13
|
Hotspots 90% C.I.
|
1
|
2
|
2
|
1
|
-
|
-
|
6
|
Hotspots 95% C.I.
|
2
|
1
|
2
|
2
|
1
|
-
|
1
|
Hotspots 99% C.I.
|
2
|
-
|
-
|
1
|
3
|
4
|
-
|
Source: Author’s computation (2021)
High-intensity clustering was reported in 2018 and 2019 in three and four LGAs respectively. This pattern of high-intensity clustering in these years could be related to high rainfall which brings about serious flooding in many parts of the state. Thus, stagnant water points tend to occur in many places and favoured ecological conditions suitable for malaria pathogens and vectors to develop and proliferate. These findings corroborate the works of Okunola and Oyeyemi, (2019) who reported malaria clusters in the 6 geopolitical zones of Nigeria, and Gambo, et al. (2020) who reported environmental influences, for example, Climate change, which has a favourable impact on the vector's ecology, habitat, and breeding grounds, as well as the study area's geographical position and poorly coordinated settlement pattern and environmental cleanliness, to have all contributed to an increase in malaria cases in Nigeria.