Epidemic curve and cluster evolution during 2020 summer
From June 21st to August 31st, a total of 257881 COVID-19 cases were registered through RENAVE. Figure 1A shows the epidemic curve, where an increasing trend of daily new cases can be appreciated beginning in July, shortly after the full lifting of control measures.
Cluster evolution followed a similar trend (Fig. 1B). Its spatio-temporal evolution can be consulted in a Shiny web application, available online at the following link: (https://coviddifusion.isciii.es/SpSumClus/) As can be observed in the viewer, at the first day of our study, June 21th, a total of 9 active clusters were active in Spain, mostly located in the north-eastern regions of Aragón, Cataluña and País Vasco, which encompass a geographical region called Ebro´s valley. Since then, and under our analysis parameters, a constant increase in the number of clusters was noted, reaching around 50 active clusters by late-July, and 100 by the second week of August.
In July, these clusters were grouped into two areas: Ebro’s valley and Madrid. The Mediterranean coast was also affected, reaching Andalucía. As the time passed, cluster distribution became more homogeneous throughout the national territory. In August, clusters had extended from Madrid to neighboring areas of Castilla-La Mancha and Castilla y León. By August 31st, cluster number had grown to 129, extending over almost every region of Spain with notable exceptions such as Asturias.
The location of the most significant cluster has changed throughout the study period. Initially, it was placed in some municipalities of Huesca and Lleida, and later, around the city of Zaragoza. Later on, it was displaced to the Barcelona metropolitan area by July 20th, and from August 8th to the surroundings of the capital city of Madrid.
A more detailed insight on the study outcomes is discussed below, focusing on two specific days (June 25th and August 1st ) as they help describe the spread of the disease in the Spanish territory (Table 2 and Map 2).
Table 2
emerging space time clusters of COVID-19 at the municipal level in Spain
Active clusters on 25th June 2020
|
Cluster
|
Active cluster period (Days)
|
P
|
Observed
|
Expected
|
RR
|
# of municipalities
|
# of municipalities with RR > 1
|
1
|
Jun 23th – Jun 25th (3)
|
< 0.001
|
122
|
4.26
|
28.85
|
28
|
15
|
2
|
Jun 24th – Jun 25th (2)
|
< 0.001
|
62
|
7.56
|
8.23
|
1
|
1
|
3
|
Jun 23th – Jun 25th (3)
|
< 0.001
|
15
|
0.42
|
35.44
|
18
|
3
|
4
|
Jun 24th – Jun 25th (2)
|
< 0.001
|
9
|
0.36
|
24.95
|
1
|
1
|
5
|
Jun 23th – Jun 25th (3)
|
< 0.001
|
4
|
0.013
|
300.36
|
1
|
1
|
6
|
Jun 23th – Jun 25th (3)
|
< 0.001
|
17
|
2.72
|
6.26
|
15
|
6
|
7
|
Jun 23th – Jun 25th (3)
|
0,004
|
6
|
0.2
|
29.61
|
2
|
2
|
Active clusters on 1st August 2020
|
Cluster
|
Active cluster period (Days)
|
p
|
Observed
|
Expected
|
RR
|
# of municipalities
|
# of municipalities with RR > 1
|
1
|
Jul 27th – Aug 1st (6)
|
0.000
|
2593
|
79.9
|
33.64
|
28
|
21
|
2
|
Jul 27th – Aug 1st (6)
|
0.000
|
4359
|
467.4
|
9.87
|
86
|
72
|
3
|
Jul 27th – Aug 1st (6)
|
0.000
|
2928
|
570.7
|
5.31
|
31
|
30
|
4
|
Jul 27th – Aug 1st (6)
|
0.000
|
574
|
24.96
|
23.18
|
40
|
31
|
5
|
Jul 27th – Aug 1st (6)
|
0.000
|
760
|
103.02
|
7.45
|
89
|
41
|
6
|
Jul 27th – Aug 1st (6)
|
0.000
|
725
|
152.98
|
4.78
|
32
|
25
|
7
|
Jul 29th – Aug 1st (4)
|
0.000
|
56
|
0.028
|
2026.62
|
1
|
1
|
8
|
Jul 27th – Aug 1st (6)
|
0.000
|
55
|
0.026
|
2094.31
|
1
|
1
|
9
|
Jul 27th – Aug 1st (6)
|
0.000
|
301
|
49.55
|
6.1
|
4
|
3
|
10
|
Jul 27th – Aug 1st (6)
|
0.000
|
176
|
13.73
|
12.84
|
73
|
23
|
11
|
Jul 27th – Aug 1st (6)
|
0.000
|
193
|
20.15
|
9.6
|
7
|
5
|
12
|
Jul 27th – Aug 1st (6)
|
0.000
|
210
|
30.13
|
6.99
|
24
|
4
|
13
|
Jul 27th – Aug 1st (6)
|
0.000
|
236
|
40.04
|
5.91
|
58
|
20
|
14
|
Jul 27th – Aug 1st (6)
|
0.000
|
122
|
7.78
|
15.71
|
17
|
10
|
15
|
Jul 27th – Aug 1st (6)
|
0.000
|
183
|
24.72
|
7.42
|
7
|
5
|
16
|
Jul 28th – Aug 1st (5)
|
0.000
|
101
|
6.94
|
14.57
|
28
|
7
|
17
|
Jul 27th – Aug 1st (6)
|
0.000
|
84
|
4.2
|
20.04
|
25
|
5
|
18
|
Jul 27th – Aug 1st (6)
|
0.000
|
265
|
68.92
|
3.86
|
34
|
24
|
19
|
Jul 27th – Aug 1st (6)
|
0.000
|
127
|
15.53
|
8.19
|
2
|
2
|
20
|
Jul 27th – Aug 1st (6)
|
0.000
|
53
|
1.26
|
42.09
|
9
|
4
|
21
|
Jul 27th – Aug 1st (6)
|
0.000
|
72
|
4.71
|
15.29
|
25
|
9
|
22
|
Jul 27th – Aug 1st (6)
|
0.000
|
71
|
4.6
|
15.45
|
29
|
4
|
23
|
Jul 27th – Aug 1st (6)
|
0.000
|
54
|
1.98
|
27.33
|
8
|
5
|
24
|
Jul 27th – Aug 1st (6)
|
0.000
|
208
|
57.8
|
3.61
|
62
|
30
|
25
|
Jul 27th – Aug 1st (6)
|
0.000
|
50
|
2.37
|
21.11
|
26
|
11
|
26
|
Jul 27th – Aug 1st (6)
|
0.000
|
95
|
13.69
|
6.95
|
21
|
13
|
27
|
Jul 27th – Aug 1st (6)
|
0.000
|
39
|
1.3
|
29.93
|
39
|
7
|
28
|
Jul 27th – Aug 1st (6)
|
0.000
|
86
|
12.44
|
6.92
|
27
|
19
|
29
|
Jul 28th – Aug 1st (5)
|
0.000
|
17
|
0.039
|
433.45
|
1
|
1
|
30
|
Jul 27th – Aug 1st (6)
|
0.000
|
179
|
56.76
|
3.16
|
56
|
34
|
31
|
Jul 27th – Aug 1st (6)
|
0.000
|
115
|
25.62
|
4.49
|
30
|
16
|
32
|
Jul 27th – Aug 1st (6)
|
0.000
|
59
|
5.84
|
10.11
|
8
|
4
|
33
|
Jul 27th – Aug 1st (6)
|
0.000
|
116
|
28.83
|
4.03
|
20
|
11
|
34
|
Jul 27th – Aug 1st (6)
|
0.000
|
51
|
4.87
|
10.47
|
29
|
7
|
35
|
Jul 27th – Aug 1st (6)
|
0.000
|
53
|
6.41
|
8.28
|
47
|
13
|
36
|
Jul 27th – Aug 1st (6)
|
0.000
|
132
|
44.53
|
2.97
|
55
|
15
|
37
|
Jul 27th – Aug 1st (6)
|
0.000
|
40
|
4.21
|
9.51
|
3
|
3
|
38
|
Jul 27th – Aug 1st (6)
|
0.000
|
30
|
2.2
|
13.62
|
16
|
2
|
39
|
Jul 31th – Aug 1st (2)
|
0.000
|
21
|
0.8
|
26.12
|
1
|
1
|
40
|
Jul 27th – Aug 1st (6)
|
0.000
|
89
|
28.98
|
3.07
|
59
|
17
|
41
|
Jul 27th – Aug 1st (6)
|
0.000
|
31
|
3.75
|
8.27
|
53
|
15
|
42
|
Jul 31th – Aug 1st (2)
|
0.000
|
38
|
6.59
|
5.77
|
39
|
5
|
43
|
Jul 27th – Aug 1st (6)
|
0.000
|
108
|
44.71
|
2.42
|
39
|
14
|
44
|
Jul 31th – Aug 1st (2)
|
0.000
|
10
|
0.16
|
63.61
|
1
|
1
|
45
|
Jul 27th – Aug 1st (6)
|
0.000
|
97
|
39.17
|
2.48
|
25
|
8
|
46
|
Jul 28th – Aug 1st (5)
|
0.000
|
78
|
28.65
|
2.72
|
1
|
1
|
47
|
Jul 30th – Aug 1st (3)
|
0.000
|
59
|
18.77
|
3.15
|
14
|
10
|
48
|
Jul 27th – Aug 1st (6)
|
0.000
|
97
|
43.82
|
2.22
|
45
|
17
|
49
|
Jul 28th – Aug 1st (5)
|
0.000
|
7
|
0.1
|
68.38
|
1
|
1
|
50
|
Jul 29th – Aug 1st (4)
|
0.000
|
13
|
0.92
|
14.08
|
10
|
5
|
51
|
Jul 28th – Aug 1st (5)
|
0.000
|
10
|
0.43
|
23.26
|
9
|
5
|
52
|
Jul 30th – Aug 1st (3)
|
0.000
|
36
|
9.45
|
3.81
|
9
|
4
|
53
|
Jul 30th – Aug 1st (3)
|
0.000
|
57
|
20.7
|
2.75
|
8
|
6
|
54
|
Jul 28th – Aug 1st (5)
|
0.000
|
51
|
17.61
|
2.9
|
50
|
10
|
55
|
Jul 28th – Aug 1st (5)
|
0.000
|
20
|
3.15
|
6.34
|
20
|
6
|
56
|
Jul 28th – Aug 1st (5)
|
0.000
|
18
|
2.54
|
7.09
|
6
|
3
|
57
|
Jul 28th – Aug 1st (5)
|
0.000
|
17
|
2.37
|
7.18
|
16
|
4
|
58
|
Jul 30th – Aug 1st (3)
|
0.000
|
23
|
4.88
|
4.72
|
54
|
12
|
59
|
Jul 27th – Aug 1st (6)
|
0.001
|
9
|
0.53
|
17.02
|
1
|
1
|
60
|
Jul 30th – Aug 1st (3)
|
0.001
|
8
|
0.38
|
20.96
|
1
|
1
|
61
|
Jul 27th – Aug 1st (6)
|
0.004
|
46
|
17.99
|
2.56
|
20
|
9
|
62
|
Jul 28th – Aug 1st (5)
|
0.004
|
33
|
10.61
|
3.11
|
13
|
7
|
RR: Relative Risk
|
Municipal- level results. June 25th, 2020.
The scan analysis for the 25th of June detected seven statistically significant emerging space-time clusters of COVID-19 are described at Table 2 and shown in Map 2A. The main cluster (cluster 1) was located between two administrative regions: Huesca (Aragón) and Lleida (Cataluña). It presented a relative risk (RR) of 28.8, with 122 observed cases compared to 4.26 expected, and it was active from June 23rd to the date of analysis. Although most cases were located in 3 municipalities, 15 out of the remaining 25 included municipalities had a RR > 1.
Other small clusters are found in the south, cluster number 2 and 4 (Málaga and Huelva) and cluster 5 in the north of Spain (Navarra), each including a single municipality. They involved 62, 9 and 4 cases, respectively, with a RR of 8.23, 24.95 and 300.36. The start date of the active cluster varies: June 23rd (cluster 2 and 4) and June 24th (cluster 5); while the following analysis date was the same (June 25th ).
Cluster 3 contains 15 municipalities, one of them shows the highest individual RR for the day of analysis (478.07). The global cluster RR was 35.44, with only 3 municipalities with a RR > 1.
Municipal-level results. August 1st, 2020.
By August 1st, 2020, 62 clusters of COVID-19 were active in Spain, present over the whole territory but two Autonomous Regions and the Autonomous Cities. They are described in Table 2 and shown in Map 2B. The number of cases ranged from 7 in the smallest aggregation to 4359 in the largest one. Cluster duration had increased and more than half of them had started five days before (on June 27th ).
An accumulation of clusters is seen in the Ebro Valley. In fact, the most significant cluster (p < 0.001) was located around the city of Zaragoza. There were 2593 incident cases from July 27th to August 1st, it had a RR of 33.64 and 21 out of the 28 municipalities included had a RR > 1. Surrounding it, there were several smaller significant clusters. One of them was the cluster 4, active for the same period, which comprised Lleida city and their close municipalities (574 cases, RR: 23.18). This area had been the most significant cluster when the analysis began.
The Mediterranean coast of Cataluña was also affected during this period. Cluster 2 is located in Barcelona and its surroundings. A total of 4359 cases were reported, affecting 86 municipalities (72 with a RR > 1) and with a RR of 9.87 for the complete aggregation.
Cluster 3 is located in the Madrid Autonomous Region and is formed by 2928 cases (RR: 5.31). It encompasses Madrid and its metropolitan area (30 of 31 municipalities with RR > 1). Around this cluster, there are 4 less-significant ones, at the rural areas of this administrative region. The remaining significant clusters can be consulted at Map 2B.
By that day, we can observe that practically most of north-eastern Spain was affected by COVID-19 clusters as well as Madrid and the Mediterranean coast, especially the south-eastern regions of Murcia, Almeria and Alicante.