Epidemiological description of cholera cases and deaths
From 2000 to 2021, the DRC recorded 520,024 suspected cases and 12,561 deaths, representing a case fatality rate of 2.4% (Fig. 2). Every province in the country and 498 of 518 (96%) health zones reported suspected cholera cases. In 2017, the DRC recorded the highest annual number of cholera cases since 2000, with more than 53,000 suspected cholera cases (Fig. 2). During the study period, the average annual case fatality rate was above 1%, thus indicating suboptimal or delayed medical treatment.
At the national level, we did not observe a significant difference in terms of numbers of cases and deaths before and during the implementation of each MCEP (p-value > 0.05) (Table I). During the pre-MCEP, MCEP-1 and MCEP-2 periods, the seasonal cholera patterns remained the same, with two epidemic peaks: a small peak towards the end of the dry season and a large peak during the middle of the rainy season. However, during the MCEP-3 period, a large epidemic peak was observed at the end of the dry season and a small peak occurred during the rainy season (Fig. 3).
Table I. Comparison of average cholera case numbers during each period.
Periods compared
|
Difference in average case numbers
|
Std. error
|
t value
|
Pr(>|t|)
|
MCEP-1 – Pre-MCEP
|
968.5
|
2431.8
|
0.398
|
0.978
|
MCEP-2 - Pre-MCEP
|
1691.9
|
2431.8
|
0.696
|
0.898
|
MCEP-3 - Pre-MCEP
|
-358.5
|
2431.8
|
-0.147
|
0.898
|
MCEP-2 – MCEP-1
|
723.4
|
2431.8
|
0.297
|
0.991
|
MCEP-3 – MCEP-1
|
-1327.0
|
2431.8
|
-0.546
|
0.947
|
MCEP-3 – MCEP-2
|
-2050.3
|
2431.8
|
-0.843
|
0.834
|
Adjusted p-values reported - single-step method. |
Biological results
From 2015 to 2021, a total of 7,518 stool samples were collected from 189,165 suspected cholera cases (collection rate: 3.9%). The highest collection rate was in 2011 (11.6%), while the lowest collection rate was in 2018 (1.3%). The culture positivity rate was 25.9% (positivity rates ranged from 43.5–11.1%) (Table II).
Table II. Distribution of suspected cholera cases, number of stool samples taken and number of positive culture samples.
Year
|
Total suspected cholera cases
|
Number of stool samples sent to the NIBR
|
Number of stool culture samples that tested positive for Vibrio cholerae O1
|
2015
|
15,444
|
1,809 (11.7%)
|
696 (38.4%)
|
2016
|
25,982
|
1,238 (4.7%)
|
252 (20.3%)
|
2017
|
54,779
|
1,000 (1.8%)
|
217 (21.7%)
|
2018
|
30,768
|
411 (1.3%)
|
146 (35.5)
|
2019
|
30,304
|
514 (1.6%)
|
224 (43.5%)
|
2020
|
19,785
|
1,340 (6.7%)
|
283 (21.1%)
|
2021
|
12,103
|
1,205 (9.9%)
|
134 (11.1%)
|
Total
|
189,165
|
7,518 (3.9%)
|
1,952 (25.9%)
|
Epidemiological description of cholera patterns in the endemic and non-endemic provinces in the DRC before and during the implementation of the MCEPs.
The highest proportions of cases were recorded by the endemic provinces, while the highest case fatality rates were reported by the non-endemic provinces. The endemic provinces recorded 438,888 suspected cases (84.4%) with a case fatality rate of 2%. The mortality rate in endemic provinces has gradually decreased, which may be due to better capacity and preparedness in terms of case management and/or improved awareness and healthcare seeking behavior among at-risk populations. Meanwhile, the non-endemic provinces reported 81,135 suspected cases (15.6%) with a case fatality rate of 4.5% (Fig. 4).
At least 75% of cases during each period (pre-MCEP, MCEP-1, MCEP-2 and MCEP-3) were recorded by the endemic provinces, i.e., 94.7%, 85.5%, 77.6% and 75.8%, respectively. However, over the course of the study period, we found that the proportion of cases in endemic provinces decreased over time, while the proportion of cases in non-endemic provinces increased (Table III and Fig. 5).
From 2000–2021, more than half of the suspected cholera cases in the endemic provinces were recorded by the provinces of South Kivu and North Kivu, with 30.1% and 25.3% of cases, respectively, followed by Tanganyika (16.1%), Haut-Lomami (13.9%), Haut Katanga (10.5%) and Ituri (3.8%). Over the course of the study period, the provinces of Tanganyika and South Kivu had the highest attack rates. Tanganyika had attack rates > 100 cholera cases per 100,000 inhabitants during all four periods. South Kivu had attack rates > 100 during the pre-MCEP and MCEP-1 periods and attack rates of 50–100 during the MCEP-2 and MCEP-3 periods (Fig. 6).
Province-level cholera risk clusters were largely concentrated in endemic provinces. During the pre-MCEP period, clusters were identified in five endemic provinces and one non-endemic province (Haut-Uélé); the risk was highest in the northeastern provinces. After the implementation of the MCEP, Ituri Province was the only endemic province not identified as a risk cluster. Apart from the endemic provinces, four non-endemic provinces were identified as risk clusters: Maniema (MCEP-1 and MCEP-2), Bas-Uélé (MCEP-1), Equateur (MCEP-1) and Kasaï-Oriental (MCEP-3) (Fig. 7).
Table III. Annual proportion of cases and deaths in the DRC per province, before and during each MCEP period.
Province
|
Pre-MCEP (2003–2007)
|
MCEP-1 (2008–2012)
|
MCEP-2 (2013–2017)
|
MCEP-3 (2018–2021)
|
Total cases (%)
|
Total deaths (%)
|
Total cases (%)
|
Total deaths (%)
|
Total cases (%)
|
Total deaths (%)
|
Total cases (%)
|
Total deaths
(%)
|
Endemic provinces
|
Haut Katanga
|
6046 (6.1)
|
213 (9.2)
|
6999 (5.7)
|
151 (7.6)
|
14605 (10.3)
|
332 (11.8)
|
9578 (10.3)
|
307 (15.0)
|
Haut Lomami
|
16780 (16.9)
|
572 (24.8)
|
7258 (4.7)
|
242 (12.2)
|
13835 (9.7)
|
324 (11.5)
|
7199 (7.7)
|
162 (7.9)
|
Ituri
|
4220 (4.2)
|
174 (7.5)
|
5812 (4.7)
|
181 (9.1)
|
4537 (3.2)
|
150 (5.3)
|
866 (0.9)
|
33 (1.6)
|
North Kivu
|
19471 (19.6)
|
447 (19.4)
|
34617 (28.2)
|
0 (0.0)
|
27744 (19.6)
|
209 (7.4)
|
15751 (16.9)
|
109 (5.3)
|
South Kivu
|
28688 (28.8)
|
252 (10.9)
|
37214 (30.3)
|
197 (9.9)
|
33638 (23.7)
|
131 (4.7)
|
22992 (24.7)
|
124 (6.1)
|
Tanganyika
|
19055 (19.1)
|
425 (18.4)
|
13152 (10.7)
|
83 (4.1)
|
15517 (10.9)
|
264 (9.4)
|
14157 (15.2)
|
184 (9.0)
|
Total endemic provinces
|
94260 (94.7)
|
2083 (90.2)
|
105052 (85.5)
|
854 (43.0)
|
109876 (77.6)
|
1410 (50.0)
|
70543 (75.8)
|
919 (44.8)
|
Non-endemic provinces
|
Bas-Uele
|
1 (0.0)
|
0 (0.0)
|
716 (0.6)
|
29 (1.4)
|
363 (0.3)
|
11 (0.4)
|
5 (0.0)
|
1 (0.0)
|
Equateur
|
9 (0.0)
|
0 (0.0)
|
2778 (2.3)
|
86 (4.3)
|
3734 (2.6)
|
126 (4.5)
|
906 (1.0)
|
57 (2.8)
|
Haut-Uele
|
0 (0.0)
|
0 (0.0)
|
437 (0.4)
|
14 (0.7)
|
1 (0.0)
|
0 (0.0)
|
1 (0.0)
|
0 (0.0)
|
Kasai oriental
|
2747 (2.8)
|
120 (5.2)
|
0 (0.0)
|
0 (0.0)
|
12 (0.0)
|
1 (0.0)
|
7839 (8.4)
|
332 (16.2)
|
Kasai
|
0 (0.0)
|
0 (0.0)
|
0 (0.0)
|
0 (0.0)
|
1384 (1.0)
|
99 (3.5)
|
1955 (2.1)
|
131 (6.4)
|
Kinshasa
|
7 (0.0)
|
0 (0.0)
|
1936 (1.6)
|
37 (1.8)
|
909 (0.6)
|
66 (2.3)
|
1355 (1.5)
|
29 (1.4)
|
Kongo central
|
280 (0.3)
|
5 (0.2)
|
1284 (1.0)
|
15 (0.7)
|
4438 (3.1)
|
126 (4.5)
|
1921 (2.1)
|
93 (4.5)
|
Kasai central
|
0 (0.0)
|
0 (0.0)
|
0 (0.0)
|
0 (0.0)
|
1 (0.0)
|
0 (0.0)
|
29 (0.0)
|
0 (0.0)
|
Kwango
|
28 (0.0)
|
6 (0.3)
|
0 (0.0)
|
19 (0.9)
|
1 (0.0)
|
0 (0.0)
|
0 (0.0)
|
0 (0.0)
|
Kwilu
|
12 (0.0)
|
0 (0.0)
|
301 (0.2)
|
0 (0.0)
|
672 (0.5)
|
46 (1.6)
|
429 (0.5)
|
39 (1.9)
|
Lomami
|
35 (0.0)
|
7 (0.3)
|
0 (0.0)
|
87 (4.3)
|
2401 (1.7)
|
96 (3.4)
|
1811 (1.9)
|
123 (6.0)
|
Lualaba
|
388 (0.4)
|
37 (1.6)
|
2426 (2.0)
|
198 (9.9)
|
590 (0.4)
|
24 (0.9)
|
1463 (1.6)
|
58 (2.8)
|
Mai-Ndombe
|
0 (0.0)
|
0 (0.0)
|
3722 (3.0)
|
14 (0.7)
|
1612 (1.1)
|
72 (2.6)
|
1369 (1.5)
|
93 (4.5)
|
Maniema
|
1615 (1.6)
|
39 (1.7)
|
560 (0.5)
|
26 (1.3)
|
6828 (4.8)
|
165 (5.9)
|
330 (0.4)
|
15 (0.7)
|
Mongala
|
0 (0.0)
|
0 (0.0)
|
544 (0.4)
|
10 (0.5)
|
3263 (2.3)
|
205 (7.3)
|
30 (0.0)
|
2 (0.1)
|
Nord Ubangi
|
0 (0.0)
|
0 (0.0)
|
0 (0.0)
|
324 (16.3)
|
443 (0.3)
|
49 (1.7)
|
1 (0.0)
|
1 (0.0)
|
Sankuru
|
130 (0.1)
|
9 (0.4)
|
0 (0.0)
|
61 (3.0)
|
507 (0.4)
|
46 (1.6)
|
2301 (2.5)
|
144 (7.0)
|
Sud Ubangi
|
1 (0.0)
|
0 (0.0)
|
837 (0.7)
|
187 (9.4)
|
12 (0.0)
|
0 (0.0)
|
10 (0.0)
|
0 (0.0)
|
Tshopo
|
19 (0.0)
|
1 (0.0)
|
1701 (1.4)
|
21 (1.0)
|
4495 (3.2)
|
274 (9.7)
|
662 (0.7)
|
11 (0.5)
|
Tshuapa
|
0 (0.0)
|
0 (0.0)
|
482 (0.4)
|
0 (0.0)
|
0 (0.0)
|
0 (0.0)
|
0 (0.0)
|
0 (0.0)
|
Total non-endemic provinces
|
5272 (5.2)
|
224 (9.7)
|
17724 (14.4)
|
1128 (56.9)
|
31666 (22.3)
|
1406 (49.9)
|
22417 (24.1)
|
1129 (55.1)
|
Evolution of cholera epidemiology in the endemic provinces
Over the entire study period, three endemic provinces (North Kivu, South Kivu and Tanganyika) recorded cases almost continuously. Tanganyika never recorded an interruption in cases of more than four weeks, while North Kivu and South Kivu each recorded a single five-week interruption during the MCEP-2 period (Fig. 8 and Table IV).
Table IV. Lulls in cholera cases of more than four weeks in the endemic provinces.
|
Number of interruptions of more than four weeks
|
Endemic provinces
|
Pre-MCEP
|
MCEP-1
|
MCEP-2
|
MCEP-3
|
South Kivu
|
0
|
0
|
1(5,5)
|
0
|
North Kivu
|
0
|
0
|
1(5,5)
|
0
|
Tanganyika
|
0
|
0
|
0
|
0
|
Haut-Lomami
|
2 (7,9)
|
2(7,9)
|
2(5,9)
|
1(7,7)
|
Haut-Katanga
|
7(5,11)
|
7(5,11)
|
4(6,10)
|
5(5,14)
|
Ituri
|
8(5,34)
|
7(5,35)
|
6(5,22)
|
6(15,32)
|
The minimum and maximum number of weeks with 0 cases are indicated in parentheses. |
Evolution of health zone cholera profiles during the three MCEP periods
A total of 14 health zones were identified as cholera sanctuary zones during MCEP-1, 14 sanctuary zones were identified during MCEP-2, and 29 sanctuary zones were identified during MCEP-3 (Table V). Six health zones were considered cholera sanctuary zones during all three MCEP implementation periods: Kalemie and Nyemba (Tanganyika), Goma and Karisimbi (North Kivu) and Uvira and Kadutu (South Kivu). These health zones recorded 24.2% of all suspected cholera cases during the study period. Four health zones identified as sanctuary zones during the MCEP-1 period were no longer considered sanctuary zones during the two subsequent MCEPs: Ibanda and Bagira (South Kivu), Kasenga and Pweto (Haut-Katanga). Sanctuary zones identified during the MCEP-3 period included all 14 sanctuary zones during the MCEP-2 period (representing 45% of the cases reported during the MCEP-3 period), 11 new health zones and four health zones identified during MCEP-1.
Table V. Health zones identified as cholera sanctuaries during each of the three MCEP periods.
Province
|
Health zone
|
MCEP-1
|
MCEP-2
|
MCEP-3
|
Haut Katanga
|
Kasenga
|
X
|
|
|
Kilwa
|
X
|
|
X
|
Pweto
|
X
|
|
|
Haut Lomami
|
Bukama
|
X
|
|
X
|
Butumba
|
X
|
|
X
|
Kabondo-Dianda
|
|
X
|
Kinkondja
|
|
X
|
X
|
Malemba-Nkulu
|
X
|
X
|
Mukanga
|
|
|
X
|
Ituri
|
Angumu
|
|
|
X
|
Bunia
|
X
|
|
X
|
Mahagi
|
|
|
X
|
Nyarambe
|
|
|
X
|
Tchomia
|
|
X
|
X
|
North Kivu
|
Goma
|
X
|
X
|
X
|
Karisimbi
|
X
|
X
|
X
|
Kirotse
|
|
X
|
X
|
Masisi
|
|
|
X
|
Mutwanga
|
|
|
X
|
Mweso
|
|
X
|
X
|
Nyiragongo
|
|
|
X
|
Rutshuru
|
|
|
X
|
South Kivu
|
Bagira
|
X
|
|
|
Fizi
|
|
X
|
X
|
Ibanda
|
X
|
|
|
Kadutu
|
X
|
X
|
X
|
Katana
|
|
|
X
|
Minova
|
|
X
|
X
|
Nundu
|
|
|
X
|
Uvira
|
X
|
X
|
X
|
Tanganyika
|
Kalemie
|
X
|
X
|
X
|
Moba
|
|
X
|
X
|
Nyemba
|
X
|
X
|
X
|
Total per period
|
14
|
14
|
29
|