Monthly data on diarrhoea in children under five years were retrieved from all health facilities and Community Health Workers (CHWs) located in the 30 districts for the period of 5 years between the January 1st, 2014 to December 31st, 2018. Monthly data on climate variables (temperature and rainfall) were available for 4 years from the January 1st, 2014 to December 31st, 2017. A total number of 1,012,827 new diarrhoeal diseases episodes were reported in outpatient consultations and by CHWs during the study period. The annual incidence rate per 100,000 population of children under five years as computed using SaTScan was 12,669 (12,669/100,000). The incidence showed an increasing tendency over time, with variation from district to another and in years (R2 = 0.24). The highest diarrhoea incidence rate (329.3/1000) was found in Kirehe district, located in Eastern province in 2017, and the lowermost incidence (48.5/100) was reported in Kamonyi, Southern province in 2016 (Table 1).
Table 1
Annual incidence rate of diarrhoeal diseases in < 5 years children at district level in Rwanda between the 1st January 2014 and 31st December 2018
| Incidence rate per 1000 < 5 years population |
District | 2014 | 2015 | 2016 | 2017 | 2018 |
Bugesera | 102.8 | 125.7 | 100.5 | 119.5 | 108.5 |
Burera | 165.6 | 213.4 | 190.9 | 222.2 | 236.1 |
Gakenke | 130.2 | 153.5 | 160.4 | 182.8 | 177.1 |
Gasabo | 133.6 | 136.2 | 110.5 | 114.7 | 107.7 |
Gatsibo | 136.7 | 128.3 | 128.6 | 170.0 | 153.7 |
Gicumbi | 77.8 | 98.4 | 100.0 | 113.5 | 118.5 |
Gisagara | 114.9 | 157.2 | 116.8 | 155.6 | 179.2 |
Huye | 110.2 | 94.6 | 80.9 | 116.9 | 127.0 |
Kamonyi | 64.3 | 55.0 | 48.5 | 70.5 | 65.2 |
Karongi | 116.6 | 114.8 | 101.9 | 123.3 | 109.1 |
Kayonza | 141.7 | 162.8 | 111.2 | 108.8 | 78.9 |
Kicukiro | 68.9 | 74.5 | 70.3 | 78.4 | 106.3 |
Kirehe | 225.5 | 254.1 | 231.8 | 329.3 | 318.7 |
Muhanga | 64.3 | 91.4 | 77.4 | 105.6 | 108.0 |
Musanze | 121.8 | 147.4 | 161.7 | 173.3 | 215.9 |
Ngoma | 193.3 | 152.2 | 115.3 | 113.4 | 103.5 |
Ngororero | 58.2 | 67.4 | 63.3 | 79.6 | 69.4 |
Nyabihu | 99.7 | 102.2 | 99.6 | 129.5 | 166.9 |
Nyagatare | 139.6 | 141.0 | 100.0 | 136.3 | 141.3 |
Nyamagabe | 83.5 | 88.5 | 72.2 | 100.8 | 122.3 |
Nyamasheke | 101.6 | 114.0 | 119.2 | 117.7 | 134.9 |
Nyanza | 90.8 | 73.9 | 58.0 | 80.6 | 108.4 |
Nyarugenge | 179.5 | 189.3 | 154.4 | 204.8 | 138.4 |
Nyaruguru | 88.1 | 89.6 | 107.2 | 140.9 | 133.0 |
Rubavu | 105.6 | 128.9 | 134.5 | 174.4 | 180.1 |
Ruhango | 81.5 | 87.1 | 69.3 | 90.7 | 111.0 |
Rulindo | 97.4 | 121.3 | 143.0 | 244.7 | 252.8 |
Rusizi | 119.6 | 128.1 | 123.7 | 143.6 | 159.5 |
Rutsiro | 141.5 | 150.3 | 131.7 | 164.5 | 161.2 |
Rwamagana | 118.9 | 102.6 | 102.8 | 123.0 | 116.8 |
Average incidence rate | 116.5 | 125.4 | 113.1 | 140.32 | 143.0 |
Purely Spatial Cluster
In 12 of total 30 districts (40%), excess risk of childhood diarrhea was reported (Fig. 1). Excess risk is expressed as a ratio of the number of observed cases over expected cases. High excess risk is indicated with a value (> 1). The northern and the eastern provinces were most at risk, three out of five districts composing the northern province were reported to be at risk and 4 out of 6 districts composing the eastern provinces. High excess risks were reported in Kirehe district (eastern province), with a Standard Morbidity Ratio (SMR) of 2.15 with a Relative Risk (RR) = 2.24, and Burera district (northern province), SMR = 1.63 with a RR = 1.66
Purely spatial clusters were identified without considering time. The clusters occurred in all provinces and the City of Kigali, seven clusters from nine locations were identified countrywide. The most likely cluster occurred in Kirehe district of the eastern provinces, with RR = 2.24 (p < 0.001) and secondary cluster observed in three out of the five districts of the northern province, Burera, Musanze and Gakenke, Log-Likelihood Ratio (LLR) = 9802.70 (p < 0.001). Least clusters occurred in southern province, in only one out of eight (1/8) districts making up the province (Table 2).
Table 2
Distribution of spatial clusters of diarrhoea in children < 5 years in Rwanda between January 1, 2014 and December 31, 2018
Cluster | District | Population | Coordinates/Radius | Obs.* | Exp.** | Annual case/100000 | Obs./Exp. | RR | LLR | P value |
1 | Kirehe | 51757 | 2.275026 S, 30.674212 E / 0 km | 70560 | 32781.93 | 27269 | 2.15 | 2.24 | 17049.9 | < 0.001 |
2 | Burera, Gakenke, Musanze | 158613 | 1.493932 S, 29.833803 E / 22.29 km | 140272 | 100462.64 | 17689.4 | 1.4 | 1.46 | 7894.5 | < 0.001 |
3 | Nyarugenge | 43271 | 1.952494 S, 30.062399 E / 0 km | 37442 | 27407.05 | 17307.8 | 1.37 | 1.38 | 1697.95 | < 0.001 |
4 | Rutsiro | 49367 | 1.959969 S, 29.385713 E / 0 km | 37028 | 31268.45 | 15002.7 | 1.18 | 1.19 | 517.51 | < 0.001 |
5 | Gatsibo | 65846 | 1.617858 S, 30.382178 E / 0 km | 48207 | 41705.42 | 14644.1 | 1.16 | 1.16 | 504.13 | < 0.001 |
6 | Gisagara | 49041 | 2.598280 S, 29.838574 E / 0 km | 35581 | 31061.58 | 14512.4 | 1.15 | 1.15 | 324.32 | < 0.001 |
7 | Rusizi | 60955 | 2.483495 S, 28.904454 E / 0 km | 41202 | 38608.04 | 13520.3 | 1.07 | 1.07 | 88.71 | < 0.001 |
RR: Relative Risk; LLR: Log-Likelihood Ratio; Obs.: number of observed cases within a cluster; Exp.: number of expected cases in a cluster |
Purely Temporal Cluster
Purely temporal clusters were identified taking into account the time only, with the unit of aggregation taken as a month, without considering space, referred to the district as the unit and scanning for clusters with high rates. These exhibited only one significant cluster in all districts (RR = 1.23, p = 0.001), from June 2017 to September 2018.
Spatiotemporal Cluster
Clusters of diarrhoeal diseases were identified considering space and time distribution (district, month and the year). In total four spatiotemporal clusters of diarrhoeal diseases in children under five years occurred between January 1, 2014 and December 31, 2018. The most likely primary cluster occurred in Kirehe district, located in eastern province (LLR = 12340.98, p < 0.001) from June 1, 2016 to October 30, 2018. The second cluster occurred in three out of the five districts constituting the northern province, namely Burera, Gakenke and Musanze (LLR = 7413.99, p < 0.001) from May 1, 2016 to October 31, 2018. The fourth cluster was observed in several districts of western and southern provinces making up 11 locations (LLR = 889.25, p < 0.001) from July 1, to September 30, 2018. The cluster involved districts composing western province (5 out 7 districts) and south province (6 out of 8 districts) (Table 3).
Table 3
Spatiotemporal distribution of diarrhoeal diseases clusters in children < 5 years in Rwanda from January 2014 and December 2018
Cluster | District | Timeframe | Population | Obs.* | Exp.** | Obs./Exp. | RR | LLR | P value |
1 | Kirehe | 2016/6/1 to 2018/11/30 | 51757 | 40419 | 16665.90 | 2.43 | 2.48 | 12340.98 | < 0.001 |
2 | Burera, Gakenke, Musanze | 2016/5/1 to 2018/10/31 | 158613 | 80000 | 51073.20 | 1.57 | 1.61 | 7413.99 | < 0.001 |
3 | Nyarugenge | 2015/5/1 to 2017/10/31 | 43271 | 20341 | 13725.91 | 1.48 | 1.49 | 1408.06 | < 0.001 |
4 | Rusizi, Nyamasheke, Karongi, Nyamagabe, Nyaruguru, Rutsiro, Huye, Nyanza, Rubavu, Ruhango,Gisagara | 2018/7/1 to 2018/9/30 | 573748 | 24900 | 18881.40 | 1.32 | 1.33 | 889.25 | < 0.001 |
Seasonal patterns of diarrhoeal diseases in children U5 years in Rwanda
A time bound consisting of 12 months of the year was considered to illustrate results taking into account variability within months. Climate variables (rainfall and temperature) were also included, to elucidate their relationship with diarrhoeal diseases, and to determine its status during rainy and dry seasons.
A bimodal rainfall was identified, increasing from February and reaching a peak in April. A decline took place in the months of May, June, July and August, reaching the lowest in July. It started to increase again from September to November, reaching a peak in November; then it started to decline again. The mean monthly temperature showed fluctuation over 12 months, with a peak in August and a secondary peak in March, reaching the lowest levels in April and November. The incidence of diarrhoeal diseases increased inversely with the rainfall, with high increases observed during the period post-rainy season (dry season) and decline with the increase of rainfall (Fig. 2).
The results of the linear regression analysis showed a statistically significant impact of maximum temperature and mean monthly rainfall on diarrhoeal disease cases. The findings revealed a positive relationship with maximum temperature, whereby the increase in one degree Celsius (1oC) was associated with an increase of 15 diarrhoea cases (95% CI, 9–20, p < 0.001). Furthermore, a negative association with mean monthly rainfall was elucidated, an increase in one millimeter (1 mm) of rainfall was observed to be associated with a decrease of 14 diarrhoeal cases (95% CI, -20, -8, p < 0.001) (Table 4).
Table 4
Relationship between monthly diarrhoea cases counts, rainfall and temperature from January 1, 2014 to December 31, 2017
Model | Unstandardized Coefficients | Standardized Coefficients | t | Sig. | 95.0% Confidence Interval for B |
B | Std. Error | Beta | Lower Bound | Upper Bound |
1 | (Constant) | 97.003 | 72.615 | | 1.336 | .182 | -45.440 | 239.446 |
Max Temperature | 17.434 | 2.830 | .160 | 6.162 | .000 | 11.884 | 22.985 |
2 | (Constant) | 201.967 | 75.731 | | 2.667 | .008 | 53.412 | 350.522 |
Max Temperature | 14.514 | 2.883 | .134 | 5.035 | .000 | 8.859 | 20.169 |
Monthly rainfall | -13.665 | 3.006 | − .121 | -4.545 | .000 | -19.563 | -7.768 |
a. Dependent Variable: Monthly counts of diarrhoeal disease Cases |