In the baseline survey, a total of 5,997 households with 23,408 people in 24 clusters were visited by the field team. Some data were missing, or some questions were not answered by household participants, these values were excluded from the analysis.
Socio-demographic information
Of the household members 53.3% (12,448/23,357) were women (table 1). The mean number of people living in a household was 3.9 (range 1–12, SD=1.9). The mean age of the study population was 35 years (range 1-105 years, SD= 21.7). The largest age group was between 35 and 64 years (35.8%; 8,375/23,365). Almost half of the study population above 5 years of age (44.9%; 10,240/22,817) reached secondary education and a significant proportion (31.9%) reached primary education. (The educational level was analysed for 5 years and older as the primary school starts at the age of 5 years in Colombia [49]). Similar characteristics were found in each cluster. (A complete description of all clusters can be found in the Additional file 3).
Table 1 Population characteristics
Characteristics
|
N*
|
Proportion %
|
Sex
Female
Male
Total (excluding 51 missing values)
Age groups
< 1 year
1-4 years
5-9 years
10-19 years
20-34 years
35-64 years
>64 years
Total (excluding 43 missing values)
median age (range)
Educational level
No school education
Primary education
Secondary education
Higher education
Total (excluding 587 missing values and 1,294 children under 5 years)
|
12,448
10,909
23,357
122
1,172
1,608
3,849
5,677
8,375
2,562
23,365
745
7,215
10,251
3,316
21,527
|
53.3%
46.7%
0.5%
5.0%
6.9%
16.5%
24.3%
35.8%
11.0%
35 (2 months-105 years)
3.5%
33.5%
47.6%
15.4%
|
*N=number of people responding excluding missing values
Peoples’ mobility
The insect vector Aedes aegypti bites primarily during the day inside or around houses and has a limited flight range; therefore, people’ mobility during the day is important to know when assessing the place of dengue transmission [50]. High mobility will make it less likely to show a protective effect by household interventions in a CRT. Therefore, we decided for a large cluster size where the majority of inhabitants move inside the protected clusters during the day. We found in the household survey that the majority of the study population (59.7%; 13,103/21,945) remains inside the cluster boundaries while a considerable proportion, 40.3% (8,842/21,945) moves to places outside their cluster where they are exposed to vector bites (table 2). A Pearson's chi-squared test was performed to compare the proportion of daytime spent outside cluster by each member of household in different population characteristics, which showed there was a statistically significant difference among sex (X2= 300.27, df=1, P=0.001), the age groups (X2= 1593.58, df=5, P=0.000) and the education level of population (X2= 1575.28, df=3, P=0.000). Those who moved outside their cluster were mainly male (53.8%; 4753/8836), young adults and adults between 20 to 64 years old (72.4%; 6,398/8,823) and people in secondary education (50.7%; 4,329/8,537).
Table 2 Demographic and socio-economic characteristics and human movements
Mobility related to sex, age and education
|
N*
|
Proportion %
|
P**
|
Mobility during daytime
Inside cluster
Outside the cluster
Total (excluding 1,463 missing values)
Sex
Female
Male
Total (excluding 6 missing values)
Age groups
<5 years
5-9 years
10-19 years
20-34 years
35-64 years
>64 years
Total (excluding 19 missing values)
Educational level
No school education
Primary education
Secondary education
Higher education
Total (excluding 174 missing values and 131 children under 5 years)
|
13,103
8,842
21,945
4,083
4,753
8,836
131
439
1,511
3,020
3,378
344
8,823
112
1,932
4,329
2,164
8,537
|
59.7%
40.3%
46.2%
53.8%
1.5%
5.0%
17.1%
34.2%
38.2%
3.9%
1.3%
22.6%
50.7%
25.3%
|
0.001
0.000
0.000
|
*N=number of people responding excluding missing values. **P-values based on Pearson's chi-squared test
Entomological information
Entomological inspections were conducted in all 5,997 households using the Standard Operational Procedures (SOPs) of the vector control services. Table 3 presents the larval and pupal indices in the 24 clusters from the three settings. The overall house index (HI) was 25.1% (1,504/5,997), the container index (CI) was 12.3% (1,776/14,386) and the Breteau index (BI) 29.6 per 100 houses (1,776/5,997) which shows high vector infestation and above the 5% assumed by WHO with the potential of epidemic disease transmission [51]. The HI was significantly different among the different clusters (σ2=0.0081, SD =0.09, range= 6%-37.6%). The CIs were generally above 3% except for cluster 22 (2.25%). The BI values were highest in cluster 23 (48.8; 122/250), cluster 12 (46.8; 118/252) and cluster 24 (45.2; 113/250) and the lowest in cluster 18 (6.8; 17/250). The Pupae per person index (PPI) varied among clusters, with a range from 0.22 to 2.04 (SD=0.49, σ2=0.2404), most PPI values being between 0.5 and 1.5, indicating a considerable risk of epidemic transmission [52].
Table 3 Vector infestation in study clusters
Cluster
|
Houses
|
Persons
|
deposits
|
Positive houses
|
Positive deposits
|
Pupae count
|
HI
|
CI
|
BI
|
PPI
|
Cucuta
|
3,997
|
15,645
|
8,541
|
1,048
|
1,240
|
13,800.4
|
26.2%
|
14.5%
|
31.02
|
0.88
|
1
|
280
|
1,130
|
600
|
94
|
102
|
1,383.7
|
33.6%
|
17.0%
|
36.43
|
1.22
|
2
|
212
|
905
|
426
|
41
|
47
|
601.2
|
19.3%
|
11.0%
|
22.17
|
0.66
|
3
|
265
|
1,050
|
557
|
72
|
82
|
504.5
|
27.2%
|
14.7%
|
30.94
|
0.48
|
4
|
235
|
894
|
358
|
45
|
49
|
192.9
|
19.1%
|
13.7%
|
20.85
|
0.22
|
5
|
230
|
844
|
554
|
81
|
94
|
985.9
|
35.2%
|
17.0%
|
40.87
|
1.17
|
6
|
250
|
861
|
743
|
72
|
76
|
582.1
|
28.8%
|
10.2%
|
30.40
|
0.68
|
7
|
272
|
965
|
607
|
42
|
43
|
960.5
|
15.4%
|
7.1%
|
15.81
|
1.00
|
8
|
247
|
663
|
563
|
88
|
105
|
1,150.2
|
35.6%
|
18.7%
|
42.51
|
1.73
|
9
|
265
|
1,066
|
342
|
87
|
95
|
1,074.5
|
32.8%
|
27.8%
|
35.85
|
1.01
|
10
|
267
|
1,064
|
358
|
50
|
57
|
1,446.7
|
18.7%
|
15.9%
|
21.35
|
1.36
|
11
|
234
|
930
|
308
|
63
|
83
|
281.2
|
26.9%
|
26.9%
|
35.47
|
0.30
|
12
|
252
|
1,179
|
703
|
82
|
118
|
290.8
|
32.5%
|
16.8%
|
46.83
|
0.25
|
13
|
223
|
962
|
737
|
60
|
92
|
1,238.3
|
26.9%
|
12.5%
|
41.26
|
1.29
|
14
|
235
|
1,000
|
313
|
80
|
89
|
696.7
|
34.0%
|
28.4%
|
37.87
|
0.70
|
15
|
250
|
968
|
735
|
37
|
49
|
724.5
|
14.8%
|
6.7%
|
19.60
|
0.75
|
16
|
280
|
1,164
|
637
|
54
|
59
|
1,686.7
|
19.3%
|
9.3%
|
21.07
|
1.45
|
Los Patios
|
1000
|
3,815
|
2,525
|
133
|
142
|
2,327.8
|
13.3%
|
5.6%
|
14.20
|
0.61
|
17
|
250
|
973
|
783
|
38
|
40
|
549.8
|
15.2%
|
5.1%
|
16.00
|
0.57
|
18
|
250
|
906
|
754
|
15
|
17
|
580
|
6.0%
|
2.3%
|
6.80
|
0.64
|
19
|
250
|
975
|
591
|
53
|
55
|
774.5
|
21.2%
|
9.3%
|
22.00
|
0.79
|
20
|
250
|
961
|
397
|
27
|
30
|
423.5
|
10.8%
|
7.6%
|
12.00
|
0.44
|
Villa del Rosario
|
1000
|
3,948
|
3,320
|
323
|
394
|
4,272.4
|
32.3%
|
11.9%
|
39.40
|
1.08
|
21
|
250
|
1,064
|
643
|
58
|
64
|
588.9
|
23.2%
|
10.0%
|
25.60
|
0.55
|
22
|
250
|
827
|
751
|
77
|
95
|
1,686.1
|
30.8%
|
12.6%
|
38.00
|
2.04
|
23
|
250
|
992
|
1,088
|
94
|
122
|
1,498.9
|
37.6%
|
11.2%
|
48.80
|
1.51
|
24
|
250
|
1,065
|
838
|
94
|
113
|
498.5
|
37.6%
|
13.5%
|
45.20
|
0.47
|
Total
|
5,997
|
23,408
|
14,386
|
1,504
|
1,776
|
20,400.6
|
25.1%
|
12.3%
|
29.61
|
0.87
|
Most infested container types
A total of 14,386 water holding containers were found in the entomological inspection. These included containers used for water storage as well as some discarded mainly small containers not used for water storage but in which water had accumulated. Overall, the most common containers were concrete ground tanks (48.5%; 6,975/14,386) of which concrete tanks for washing purposes (79.3%; 5,528/6,975) were the most common ones (Figure 2). Other container types included elevated tanks (24.5%; 3,529/14,386), plastic tanks (11.3%; 3,529/14,386) and buckets (10.1%; 1,446/14,386). Among the positive containers, the most infested water containers with Aedes aegypti larvae were ground tanks for cleaning and washing purposes (71.9 %, 1277/14,386). Table 4 shows the distribution of water containers. The distribution of containers was similar in all clusters. (A description of the distribution of containers per cluster and setting can be found in the additional file 3).
Figure 2
Pupal productivity in different water container types
The total number of Aedes aegypti pupae collected across all cluster was 20,400. Of these 13,800 pupae were collected from the clusters in Cucuta (271 households) with a median of 50.9 total pupae per household; 2,328 pupae were collected from the 4 clusters of the municipality of Los Patios (80 households) with a median of 29.1 and 4,272 from the 4 clusters in the municipality of Villa del Rosario (190 households) with a median of 22.5 pupae per household.
The water container type with the highest proportion of pupae was the concrete ground tank, producing 94.5% of all pupae as a proxy for the production of adult mosquitoes (table 4). From these, tanks for washing and cleaning (lavaderos) were noticeably the most productive water containers for Aedes vector (86.3%). This is probably related to the fact that most of these ground tanks were uncovered and outside of the house. Less important for pupal production were plastic tanks, producing 3.4% of pupae and least important were buckets, elevated tanks and metal barrels, producing together only 2.0% of pupae (table 4).
Table 4 Types of water containers inspected and pupae productivity
Type of containers
|
# containers
|
%
|
Positive container
|
(%)
|
Pupae count (n)
|
% Productivity
|
Concrete ground laundry tank (lavadero)
|
5,528
|
38.4%
|
1,277
|
23.1%
|
17,613.2
|
86.3%
|
Concrete ground tank for water storing
|
1,447
|
10.1%
|
119
|
8.2%
|
1,661.1
|
8.1%
|
Plastic tank
|
1,624
|
11.3%
|
119
|
7.3%
|
688.8
|
3.4%
|
Buckets
|
1,446
|
10.1%
|
138
|
9.5%
|
238
|
1.2%
|
Elevated tank
|
3,529
|
24.5%
|
30
|
0.9%
|
124
|
0.6%
|
Metal barrel
|
137
|
1.0%
|
30
|
21.9%
|
46.5
|
0.2%
|
Sinks
|
67
|
0.5%
|
6
|
9.0%
|
8
|
0.0%
|
Flowerpot
|
95
|
0.7%
|
21
|
22.1%
|
8
|
0.0%
|
Others (including natural habits)
|
72
|
0.5%
|
9
|
14.1%
|
5
|
0.0%
|
Jars/pots
|
118
|
0.8%
|
5
|
4.2%
|
4
|
0.0%
|
Wheels
|
75
|
0.5%
|
15
|
20.0%
|
4
|
0.0%
|
Fuel jars (pimpinas)
|
121
|
0.8%
|
3
|
2.5%
|
0
|
0.0%
|
Water bottles
|
127
|
0.9%
|
4
|
3.1%
|
0
|
0.0%
|
Total
|
14,386
|
|
1,776
|
12.3%
|
20,400.6
|
|
Pupal productivity: n*= total number of pupae for all containers of that type; %* = (total number of pupae from that container type/overall total number of pupae) × 100.
Ground tanks and water use
Characteristics of the concrete ground tanks (lavaderos) were similar in all clusters. Most of them were mainly used for washing and cleaning, without a lid (92.5 %; 5,017/5,421) and located outdoors (60.1%; 3,259/5,421). The mean number of ground tanks was 1 per household (SD= 0.41, range=0-4). Overall, the mean capacity of these containers was 363 L (range 20 L to 5,000 L). Traditionally, these ground tanks have been treated by house owners with another no-standardized vector control method, chlorine tablets, which are self-applied by a member of household. Almost half of participant households (46.4%) reported ever having applied chlorine tablets, however the doses and frequency of application was variable. A small proportion (6.8%) of the population reported to use fish as biological control in these containers.
Regarding the sources of drinking water, only 2.2% (133/5,997) of the houses take drinking water from these ground tanks while the majority uses it for laundry (97.8%) and drink water from the tap provided by the municipal water company. We observed in our survey that people had quite a strict separation of the water sources for drinking and cleaning or washing (water mostly from ground tanks or plastic tanks). Drinking water also is used for cooking, showering and flush toilets.
Epidemiological information
Across all clusters, 2.0% (468/23,093) of household members reported to have had any arboviral disease (DZC) during the last 12 months (Dengue incidence was 0.84%). This ranged from 3.0% (116/3,814) in Los Patios, 2.3% (90/3,948) in Villa del Rosario, to 1.7% (262/15,331) in Cucuta. A small group of respondents (68 persons) assumed to have had mixed infections with two arbovirus diseases. The 12-months self-reported incidence was the following: dengue 841.6 per 100,000 inhabitants, Zika 585.3 per 100,000 inhabitants and chikungunya 572.45 per 100,000 inhabitants. Persons with dengue (83.2%) usually went for diagnosis and treatment to the hospital while persons with Zika or Chikungunya used much less the hospital services (45.3% and 57.5% respectively). Fig. 2 shows the reported Dengue incidence rate by study population in 24 clusters. Los Patios (1,965.9 per 100,000 inhabitants) and Villa del Rosario (1,494.4 per 100,000) noticeably had a higher dengue incidence rate than Cucuta (402.9 per 100,000). Cluster 18 had the highest dengue incidence rate (2,869.8 per 100,000 inhabitants) and clusters 2, 9 and 14 did not report any dengue case (figure 3).
Figure 3
Table 5 shows the annual incidence of self-reported DZC related to sociodemographic characteristics (statistically significant differences except for education level). Females had a higher incidence (2.3%; 285/12,448) than males (1.7%; 185/10,909) (X2= 11.09, df=1, P=0.001). Younger age groups, particularly those between 5 and 9 years of age (3.7%; 60/1,608) reported more cases of arbovirus diseases in comparison with other age groups (X2= 32.66, df=6, P=0.001). Educational level (as an indicator for socioeconomic characteristics) was not associated with disease incidence People who stayed inside their clusters during the day had a higher incidence (2.2%; 291/13,103) than those who move during daytime outside their home DZC (1.7%, 146/8,842; X2=8.778, df=1, P=0.03).
Table 5 Self-reported annual incidence of DZC by different variables
Characteristic
|
Frequency of DZC during last 12 months % (N/d)*
|
P**
|
Sex
Female
Male
Age groups
< 1 year
1-4 years
5-9 years
10-19 years
20-34 years
35-64 years
>65 years
Education level
No education
Primary education
Secondary education
Higher education
Regular daily activity
Inside cluster
Outside cluster
|
2.3% (285/12,448)
1.7% (183/10,909)
0.8% (1/122)
2.5% (29/1,172)
3.7% (60/1,608)
1.9% (73/3,849)
1.7% (99/5,677)
1.8% (147/8,375)
2.3% (59/2,562)
2.1% (16/745)
2.1% (152/7,215)
1.8% (187/10,251)
2.2% (73/3,316)
2.2% (291/13,103)
1.7% (146/8,842)
|
0.001
0.001
0.423
0.03
|
*N=number of people who reported to have had dengue; d=total number of people who responded. **p-values based on Pearson's chi-squared test
Dengue incidence notified by the National surveillance system, 2015–2021
During the 7-year period, 2015–2021, 8,190 dengue cases were notified by SIVIGILA in the study areas. The number of annual case notifications varied from a low of 333 cases in 2020 (173.1 per 100,000 population) to a high of 1,949 cases in 2019 (1,013.4 per 100,000 population), with a mean of 1,170 cases per year (incidence 608.4 per 100,000 population). Across all clusters, the number of dengue cases varied with a range of 4 to 193 dengue cases between 2015-2021. Cluster 14 had the lowest dengue incidence rate (51.1 per 100,000 population) in 2020 and Cluster 5 had the highest incidence rate (2,933.8 per population (see table 6). Patients with fever and other DZC symptoms resort to the health services only when they feel severely sick.
Table 6 Annual dengue incidence per 100,000 people notified by SIVIGILA (2015-2021)
Cluster
|
2015
|
2016
|
2017
|
2018
|
2019
|
2020
|
2021
|
1
|
870.7
|
245.3
|
220.8
|
686.8
|
1,410.4
|
245.3
|
1,802.8
|
2
|
607.5
|
341.7
|
88.6
|
734.1
|
1,151.8
|
139.2
|
1,316.3
|
3
|
564.3
|
435.3
|
322.5
|
645.0
|
1,015.8
|
225.7
|
854.6
|
4
|
557.1
|
330.8
|
243.7
|
1,532.0
|
1,410.2
|
139.3
|
1,009.7
|
5
|
1,420.1
|
764.7
|
577.4
|
1,201.6
|
2,933.8
|
577.4
|
811.5
|
6
|
776.8
|
263.1
|
263.1
|
839.5
|
814.4
|
137.8
|
451.1
|
7
|
298.5
|
155.2
|
107.5
|
418.0
|
835.9
|
107.5
|
238.8
|
8
|
981.7
|
387.5
|
374.6
|
632.9
|
1,433.7
|
439.2
|
426.2
|
9
|
608.6
|
294.5
|
215.9
|
981.5
|
795.1
|
157.0
|
647.8
|
10
|
501.6
|
178.4
|
156.1
|
802.6
|
412.4
|
78.0
|
646.5
|
11
|
520.8
|
186.7
|
147.4
|
668.2
|
599.4
|
78.6
|
343.9
|
12
|
824.8
|
477.5
|
130.2
|
1,128.7
|
803.1
|
238.8
|
2,452.8
|
13
|
905.6
|
235.7
|
285.3
|
372.2
|
2,009.7
|
173.7
|
831.2
|
14
|
664.5
|
127.8
|
115.0
|
805.0
|
396.1
|
51.1
|
907.2
|
15
|
583.3
|
272.2
|
108.9
|
840.0
|
770.0
|
147.8
|
754.5
|
16
|
990.2
|
452.1
|
301.4
|
1,819.0
|
2,077.3
|
236.8
|
1,410.0
|
17
|
301.2
|
283.4
|
301.2
|
513.7
|
974.3
|
230.3
|
885.7
|
18
|
331.0
|
296.8
|
159.8
|
993.0
|
707.7
|
57.1
|
764.8
|
19
|
224.4
|
366.2
|
248.1
|
826.8
|
1,169.4
|
141.7
|
685.1
|
20
|
555.9
|
465.4
|
245.6
|
1,745.3
|
736.9
|
116.4
|
452.5
|
21
|
1,395.8
|
197.2
|
227.6
|
1,395.8
|
880.0
|
197.2
|
1,213.8
|
22
|
1,252.1
|
445.5
|
337.1
|
1,131.7
|
517.7
|
96.3
|
565.9
|
23
|
496.6
|
264.9
|
242.8
|
1,390.6
|
640.1
|
121.4
|
684.3
|
24
|
605.1
|
357.5
|
288.8
|
1,883.9
|
440.0
|
233.8
|
1,265.1
|
Overall
|
688.4
|
316.1
|
230.3
|
989.0
|
1,013.4
|
173.1
|
848.6
|
Willingness to receive a new vector control intervention
The community in all clusters was interested in receiving the proposed novel vector control method (insecticidal coating for water containers). Overall, 88.3% of respondents held this view and there was no significant difference between clusters (5,296/5,997). The experience of the vector control staff (24 inspectors) was assessed through a short questionnaire; they considered that this study was very useful and interesting for improving public health in the city particularly regarding vector borne diseases, but they wanted to receive more training on arbovirus diseases and all of them would like to participate in the next phase of the study.