Supplement for the manuscript ‘Integrated monitoring and evaluation and
enviromental risk factors for urinary schistosomiasis and active trachoma in Burkina
Faso before preventative chemotherapy, using sentinel sites’
S.1
Below the reviewers can find some more details in describing the basis on how the sample
size was estimated. In order to calculate sample sizes for this study, we have used in these
calculations longitudinal monitoring data from the National Vertical Schistosomiasis
Control Program (NVSCP) in Burkina Faso which were already collected during 20042006. For instance, an overall drop-out rate of 55% comparing survey 3 to survey 1 was
observed in these NVSCP longitudinal monitoring data during 3 annual surveys over the
course of the monitoring period and this was also incorporated in our sample size
calculations. EpiSchisto was also used to get predictions within the integration era (i.e.
“post-treatment environment” as there was the NVSCP before the integration) where as a
starting point of the integrated programme, we used the most recent available NVSCP data
at the time (from the 3rd annual survey, i.e. follow-up year 2 during 2006).
The relationship between prevalence and intensity of S. haematobium infection was
assumed to arise from a negative binomial distribution of parasites among hosts in order to
estimate using maximum likelihood the inverse overdispersion (k) parameter required to
parameterise the EpiSchisto program.
Figures 1A and 1B below illustrate these calculations, respectively, for pre-treatment
baseline (2004) and 2nd year post-treatment (2006) from the NVSCP longitudinal
monitoring data. In addition, these figures show that k values change over time with the
intervention-a finding we took into account in the sample size calculations.
1
Figure S.1
A
Prevalence vs. Mean intensity of S. haematobium infection in Burkina Faso at
baseline
100
90
Prevalence of infection (%)
80
70
60
observed
50
expected
40
30
20
10
0
100
0
200
300
400
500
600
800
700
900
1000
Mean intensity (e/10 ml)
B
Prevalence vs. Mean intensity of S. haematobium infection in Burkina Faso at follow-up
year 2
100
90
observed
80
Prevalence of infection (%)
70
expected
60
50
40
30
20
10
0
0
10
20
30
40
50
60
70
80
Mean intensity (e/10 ml)
Points represent observed data of 763 Burkinabé children while the green line represents the fitted
prevalence according to a negative binomial model with the overdispersion k parameter as a linear function
2
of the arithmetic mean infection intensity (m) with expression k(m)= k0+k1m. Parameters for baseline were
k0 = 0.050 and k1 = 0.001 and for the follow-up year 2 were k0 =0.017, and k1 = 0.0006. The figures above
indicate that k values change over time with the intervention. This was taken into consideration in the
calculations of the sample sizes.
S.2
Below the reviewers can find two tables that contain Pearson correlations. The first table
(i.e. Table S.1) contains correlations between the average values of weather and
environmental variables as derived from the 9 weather stations.
The second table (i.e. Table S.2) contains Pearson correlations between the school-level
prevalences of single and dual infections (i.e. n=21) with the interpolated values of the
weather and environmental variables through inverse distance weighting (i.e. assigned
values to unknown points of weather and environmental variables for schools from the
known average values as derived from the weather stations).
Table S.1
Mean
altitude
Mean
precipitation
Mean max
temp
Mean
1
altitude
Mean
0.410
1
precipitation
p=0.273
Mean max
1
-0.711
-0.825
temp
p=0.032
p=0.006
Mean min
-0.435
0.650
-0.677
temp
p=0.241
p=0.058
p=0.045
Mean
av
-0.359
-0.885
0.800
temp
p=0.342
p=0.002
p=0.010
Mean
air
-0.639
-0.284
0.623
pressure
p=0.064
p=0.459
p=0.073
*Statistically significant at the 0.05 significance level
Mean min
temp
Mean
temp
av
Mean air
pressure
1
0.875
p=0.002
-0.047
p=0.905
1
0.096
p=0.806
1
3
Table S.2
Air pressure◊
Av temperature◊
Max temperature◊
Min temperature◊
Precipitation◊
Altitude◊
S. haematobium
prevalence◙
Active trachoma
prevalence◘
0.413
p=0.063
0.543
p=0.011
0.688
p<0.001
0.440
p=0.046
-0.631
p=0.002
-0.595
p=0.005
-0.762
p<0.001
-0.399
p=0.073
-0.693
p<0.001
-0.384
p=0.086
0.470
p=0.031
0.771
p<0.001
Prevalence of coinfections with S.
haematobium and
active trachoma□
0.331
p=0.143
0.342
p=0.129
0.424
p=0.055
0.274
p=0.230
-0.436
p=0.048
-0.411
p=0.064
◊ Interpolated values of environmental variables.
◙ S. haematobium prevalence at the school level (single infections with S. haematobium and co-infections
with active trachoma are included in these calculations).
◘ Active trachoma prevalence at the school level (single infections with active trachoma and co-infections
with S. haematobium are included in these calculations).
□ Only co-infections with S. haematobium and active trachoma at the school level are included in these
calculations.
S.3
Scatter plots are displayed below to show values for the interpolated values of the
environmental variables and the school-level prevalences of single and dual infections.
Initially six scatter plots are displayed for the S. haematobium prevalences at the school
level and the interpolated values of the environmental variables; then another six scatter
plots are displayed between the active trachoma prevalences at the school level and the
interpolated values of the environmental variables. Finally six scatter plots are displayed
for the prevalences of co-infections with S. haematobium and active trachoma at the school
level and the interpolated values of the environmental variables.
4
60
S. haematobium school prevalence
S. haematobium school prevalence
60
50
40
30
20
10
0
960
965
970
975
50
40
30
20
10
0
27
980
27.5
28
29
29.5
30
school prevalence
60
50
40
30
S. haematobium
S. haematobium
school prevalence
60
20
10
0
33
34
35
36
37
38
50
40
30
20
10
0
21.5
22
Max temperature (celsius)
22.5
23
23.5
Min temperature (celsius)
60
school prevalence
60
50
40
30
S. haematobium
S. haematobium school prevalence
28.5
Av temperature (celsius)
Air pressure (millibar)
20
10
0
0
0.5
1
1.5
2
Precipitation (mm)
2.5
3
3.5
50
40
30
20
10
0
0
100
200
300
400
500
Altitude (MSL)
Points at all the six scatter plots above show S. haematobium prevalence at the school level (single
infections with S. haematobium and co-infections with active trachoma are included in these calculations)
versus the interpolated values of the environmental variables.
5
40
35
35
Active
trachoma school prevalence
Active trachoma school
prevalence
40
30
25
20
15
10
5
30
25
20
15
10
5
0
0
960
965
970
975
27
980
27.5
28
29
29.5
30
40
Active trachoma school prevalence
Active trachoma school prevalence
40
35
30
25
20
15
10
5
35
30
25
20
15
10
0
33
34
35
36
37
38
5
0
21.5
22
22.5
23
23.5
Min temperature (celsius)
M ax temperature (celsius)
40
40
35
35
30
30
Active trachoma
school prevalence
Active trachoma school prevalence
28.5
Av temperature (celsius)
Air pressure (millibar)
25
20
15
25
20
15
10
10
5
5
0
0
0
0
0.5
1
1.5
2
2.5
3
3.5
100
200
300
400
500
Altitude (MSL)
Precipitation (mm)
Points at all the six scatter plots above show active trachoma prevalence at the school level (single
infections with active trachoma and co-infections with S. haematobium are included in these calculations)
versus the interpolated values of the environmental variables.
6
4.5
4
Co-infections school prevalence
Co-infections school prevalence
4.5
3.5
3
2.5
2
1.5
1
0.5
0
960
965
970
975
4
3.5
3
2.5
2
1.5
1
0.5
0
980
27
27.5
28
Air pressure (millibar)
29
29.5
30
4.5
4.5
4
Co-infections school prevalence
Co-infections school prevalence
28.5
Av temperature (celsius)
3.5
3
2.5
2
1.5
1
0.5
4
3.5
3
2.5
2
1.5
1
0.5
0
21.5
0
33
34
35
36
37
22
38
22.5
23
23.5
Min temperature (celsius)
Max temperature (celsius)
4.5
4
Co-infections school prevalence
Co-infections school prevalence
4.5
3.5
3
2.5
2
1.5
1
0.5
0
0
0.5
1
1.5
2
Precipitation (mm)
2.5
3
3.5
4
3.5
3
2.5
2
1.5
1
0.5
0
0
100
200
300
400
500
Altitude (MSL)
Points at all the six scatter plots above show prevalences of co-infections at the school level (single
infections are not included in these calculations) versus the interpolated values of the environmental
variables.
7
8