Background
Methods
Study population
Dependent variable
Individual and collective data
Environmental data
Exposition location
NDVI
Weather data
Urban mapping
Data construction
Statistical analysis
Ethical clearance
Results
Clinical malaria-free (n =4 400) | Clinical malaria (n =131) | p | ||
---|---|---|---|---|
Age (in years) * | 25 [22–29] | 25 [22–28] | 0.43 | |
Manager † | ||||
No | 3 245 (74%) | 109 (84%) | ||
Yes | 1 141 (26%) | 21 (16%) |
0.006
| |
Year of stay † | ||||
2003 | 767 (17%) | 8 (6%) |
0.0001
| |
2004 | 1 926 (44%) | 86 (66%) |
>0.0001
| |
2005 | 1 288 (29%) | 29 (22%) |
0.04
| |
2006 | 419 (10%) | 8 (6%) | 0.12 | |
Number of sites visited during the stay † | ||||
<10 sites | 3 377 (77%) | 92 (70%) | ||
≥10 sites | 1 023 (23%) | 39 (30%) |
0.05
| |
Average length of stay by site † | ||||
<15 days | 1341(30%) | 41 (31%) | ||
≥15 days | 3 059 (70%) | 90 (69%) | 0.45 | |
Characteristics of the sites of stay | ||||
Cumulated precipitation (mm of water) * | 89 [67–122] | 96 [71–157] |
0.008
| |
Mean Evapotranspiration (mm) * | 113 [105–123] | 111 [105–128,6] | 0.50 | |
Mean Water balance (mm) * | −36 [(−)62 - (+)13] | −25 [(−)52 - (+)59] |
0.008
| |
Mean Minimum temperature (Celsius) * | 20.3 [19.5-22.5] | 20.0 [18.9-21.1] |
0.0005
| |
Mean temperature (Celsius) * | 27.5 [25.3-27.5] | 27.5 [25.2-27.5] | 0.21 | |
Mean Maximum temperature (Celsius) * | 32.8 [31.5-35.5] | 32,9 [31.4-35.7] | 0.95 | |
Mean number of Consecutive dry days § (in days/month) * | 3.2 [1.9 – 7.0] | 3.1 [1.1 – 6.3] |
0.004
| |
Proportion of time spent in urban area * | 81 [23–100] | 64 [15 – 89] |
0.0007
| |
NDVI mean (0 month of decay) * | 0.39 [0.29 – 0.53] | 0.39 [0.31 – 0.52] | 0.65 | |
NDVI mean (1 month of decay) * | 0.38 [0.30 – 0.50] | 0.39 [0.30 – 0.52] | 0.44 | |
NDVI mean (2 months of decay) * | 0.38 [0.31 – 0.49] | 0.41 [0.31 – 0.54] |
0.07
|
Univariate analysis
Individual variables
Number of clinical malaria attacks | Number of individuals | Number of person-days under survey | Incidence rate per 1,000 person-month | RR | 95% CI | p | |
---|---|---|---|---|---|---|---|
Age
| |||||||
18 - 24 y | 66 | 2 087 | 262 561 | 7.65 | 1 | ||
25 - 29 y | 49 | 1 432 | 178 907 | 8,33 | 1,12 | 0,77 - 1,64 | 0,54 |
30 - 39 y | 22 | 866 | 110 038 | 6,08 | 0,82 | 0,50 - 1,34 | 0,43 |
40 - 56 y | 3 | 137 | 17 568 | 5.19 | 0,74 | 0,23 - 2,44 | 0,63 |
Manager
| |||||||
No | 117 | 3 223 | 405 122 | 8.48 | 1 | ||
Yes | 23 | 1 308 | 167 240 | 4.91 | 0,596 | 0,380 - 0,935 | 0,024 |
Age and manager status
| |||||||
Manager | 23 | 1 162 | 146 591 | 4.77 | 1 | ||
Non Manager | |||||||
18 - 19 y | 7 | 256 | 32 198 | 6.61 | 1,19 | 0,51 - 2,81 | 0,682 |
20 - 24 y | 53 | 1 607 | 203 061 | 7.94 | 1,62 | 0,96 - 2,58 | 0,074 |
≥25 y | 57 | 1 491 | 188 744 | 9.19 | 1,90 | 1,16 - 3,09 | 0,010 |
Year of arrival in Ivory Coast
| |||||||
2002, 2003, 2005 or 2006 | 49 | 2 519 | 298 597 | 4.99 | 1 | ||
2004 | 91 | 2 012 | 273 766 | 10.1 | 1,80 | 1,10 - 2,97 | 0,020 |
Number of sites visited
| |||||||
<10 sites | 98 | 3 469 | 430 613 | 6.78 | 1 | ||
≥10 sites | 42 | 1 062 | 141 750 | 9.01 | 1,454 | 0,866 - 2,442 | 0,157 |
Average duration of the stay by site
| |||||||
<15 days | 44 | 1 382 | 164 372 | 8.14 | 1 | ||
≥15 days | 96 | 3 149 | 407 991 | 7.16 | 0,813 | 0,486 - 1,360 | 0,43 |
Collective variables
Environmental and meteorological variables
Number of clinical malaria attacks | Number of individuals | Number of person-days under survey | Incidence rate per 1,000 person-month | RR | 95% CI | p | |
---|---|---|---|---|---|---|---|
Cumulated precipitation
| |||||||
>180 mm of water by month*
| |||||||
<33% duration of stay | 94 | 3665 | 454 512 | 2,52 | 1 | ||
≥33% duration of stay | 46 | 866 | 117 851 | 4,75 | 1,69 | 0,87 - 3,26 | 0,120 |
Water balance
| |||||||
> +15 mm of water by month*
| |||||||
<66% duration of stay | 83 | 3447 | 425 615 146 748 | 5,93 | 1 | ||
≥66% duration of stay | 57 | 1084 | 146 748 | 11,81 | 1,82 | 1.05 – 3.16 | 0,032 |
Consecutive dry week
| |||||||
number of consecutive dry weeks in month
| |||||||
By week (in continuous) | 0,93 | 0,864 - 1,01 | 0,085 | ||||
Evapotranspiration
| |||||||
>150 mm of water by month
| |||||||
<33% duration of stay | 120 | 4062 | 508 236 | 2,87 | 1 | ||
≥33% duration of stay | 20 | 469 | 64 127 | 3,80 | 1,31 | 0,58 - 2,95 | 0,518 |
Maximal temperature
| |||||||
>30°C | |||||||
<66% duration of stay | 9 | 485 | 64 218 | 1,71 | 1 | ||
≥66% duration of stay | 131 | 4 046 | 508 145 | 3,14 | 1,53 | 0,61 - 3,87 | 0,368 |
Mean temperature
| |||||||
>25°C | |||||||
< 66% duration of stay | 55 | 1 196 | 158 856 | 4,22 | 1 | ||
≥66% duration of stay | 85 | 3 335 | 413 507 | 2,50 | 0,73 | 0,419 - 1,28 | 0,271 |
Mean temperature
| |||||||
By degree Celsius (in continuous) | 0,95 | 0,79 - 1,15 | 0,629 | ||||
Minimal temperature
| |||||||
>20°C | |||||||
< 33% duration of stay | 38 | 693 | 93 009 | 4,97 | 1 | ||
≥33% duration of stay | 102 | 3 838 | 479 354 | 2,59 | 0,56 | 0,27 - 1,16 | 0,120 |
Urban area
| |||||||
<33% duration of stay | 57 | 1 191 | 157 480 | 4,41 | 1 | ||
≥33% duration of stay | 83 | 3 340 | 414 883 | 2,44 | 0,50 | 0,30 - 0,86 | 0,011 |
Number of clinical malaria attacks | Number of individuals | Number of person-days under survey | Incidence rate per 1,000 person-month | RR | 95% CI | p | |
---|---|---|---|---|---|---|---|
NDVI
| |||||||
NDVI (M0)* >0,35
| |||||||
< 66% duration of stay | 70 | 2 391 | 298 185 | 7.14 | 1 | ||
≥66% duration of stay | 70 | 2 140 | 274 178 | 7.76 | 1,10 | 0,66 - 1,83 | 0,724 |
NDVI (M-1)* >0,35
| |||||||
< 66% duration of stay | 77 | 2 730 | 342 844 | 6.83 | 1 | ||
≥66% duration of stay | 63 | 1 801 | 229 519 | 8.35 | 1,33 | 0,80 - 2,23 | 0,268 |
NDVI (M-2)* >0,35
| |||||||
< 66% duration of stay | 77 | 2 890 | 365 385 | 6.41 | 1 | ||
≥66% duration of stay | 63 | 1 641 | 206 978 | 9.26 | 1,60 | 0,97 - 2,66 | 0,067 |
Multivariate analysis
RR | IC95% | P | |
---|---|---|---|
Age and manager status
| |||
Manager | 1 | ||
Non Manager | |||
18 - 19 years old | 1,19 | 0,51 - 2,80 | 0,685 |
20 - 24 years old | 1,65 | 1,01 - 2,71 | 0,046 |
≥25 years old | 1,92 | 1,18 - 3,12 | 0,008 |
Arrival date in 2004
| |||
No | 1 | ||
Yes | 4,99 | 2,72 - 9,14 | < 0,001 |
NDVI ≥0,35 (2 month before) | |||
<66% duration of stay | 1 | ||
≥66% duration of stay | 2,42 | 1,48 - 3,97 | < 0,001 |
Number of consecutive dry week in month, in continuous
| 1 | ||
+1 consecutive dry week in month | 0,275 | 0,14 - 0,52 | < 0,001 |
Mean temperature
| |||
<27°C | 1 | ||
≥27°C | 2,40 | 1,30 - 4,42 | 0,005 |
Group-specific random effect (i.e. group effect) | 0,048 |