Background
Methods
Study setting
Study design and participants
Sample size estimation
Data collection
Definition and follow up of outcome variables
Attrition
Attrition for known outcome
Attrition for unknown outcome
Physical integrity
Functional survivorship
Bio-efficacy
Statistical analysis
Ethical considerations
Results
Characteristics of study households
Variable | n (%) |
---|---|
Gender of head of household | |
Male | 407 (61.8) |
Female | 252 (38.2) |
Educational status of head of household (n = 647) | |
Illiterate | 369 (57.0) |
Read and write | 59 (9.1) |
Primary | 162 (25.0) |
Secondary and above | 57 (8.8) |
Wealth status (n = 622) | |
Poor | 230 (37.0) |
Middle | 198 (31.8) |
Rich | 194 (31.2) |
Family size | |
≤ 5 | 328 (49.8) |
> 5 | 331 (50.2) |
House with open eave gap (n = 615) | |
Yes | 99 (16.1) |
No | 516 (83.9) |
Distance from mosquito breeding site (km) | |
≤ 1 | 202 (30.7) |
> 1 | 457 (69.3) |
Enrollment of LLINs and study completion
Attrition
Reason for LLIN loss | 6 months n (%) | 12 months n (%) | 18 months n (%) | 24 months n (%) | Total n (%) |
---|---|---|---|---|---|
Known outcome of attrition or torn | |||||
Thrown away | 102 (40.0) | 301 (71.8) | 173 (74.9) | 62 (70.5) | 638 (64.2) |
Used for something else | 30 (11.8) | 58 (13.8) | 28 (12.1) | 22 (25.0) | 138 (13.9) |
Torn (pHI > 643) | 123 (48.2) | 60 (14.3) | 30 (13.0) | 4 (4.5) | 217 (21.9) |
Total | 161 (100) | 331.1 (100) | 149 (100) | 12 (100) | 993 (100) |
Unknown outcome of attrition | |||||
Given away | 260 (76.7) | 44 (45.8) | 11 (20.0) | 1 (12.5) | 316 (63.5) |
Lost to follow-upa | 52 (15.3) | 43 (44.8) | 26 (47.2) | 5 (62.5) | 126 (25.3) |
Stolen | 8 (2.4) | 9 (9.4) | 3 (5.5) | 2 (25.0) | 22 (4.4) |
Unknown reasons | 6 (1.8) | 0 (0.0) | 1 (1.8) | 0 (0.0) | 7 (1.4) |
Otherb | 13 (3.8) | 0 (0.0) | 14 (25.5) | 0 (0.0) | 27 (5.4) |
Total | 461 (100) | 558.2 (100) | 153 (100) | (168) (100) | 498 (100) |
Physical integrity
Characteristic | 6 months N = 833 | 12 months N = 410 | 18 months N = 159 | 24 months N = 39 |
---|---|---|---|---|
Holes (size categories 1–4), n (%) | 298 (35.8) | 204 (49.8) | 107 (67.3) | 31 (79.5) |
Mean (SD) number of holes | ||||
Lower half segment of nets | 3.7 (12.7) | 4.2 (12.0) | 5.7 (13.3) | 4.4 (6.6) |
Upper half segment of nets | 2.1 (8.1) | 2.2 (4.6) | 3.7 (8.1) | 5 (9.2) |
Roof segment of nets | 1.2 (4.9) | 1.8 (4.6) | 2.6 (4.5) | 3.3 (3.8) |
GM pHI (95% CI)a | 216 (167–279) | 251 (195–323) | 316 (234–427) | 211 (117–378) |
Median pHI (IQR)a | 270 (48–993) | 275 (88–843) | 422 (173–775) | 296 (77–604) |
Category defined by pHI | 6 months N = 833 n (%) | 12 months N = 410 n (%) | 18 months N = 159 n (%) | 24 months N = 39 n (%) |
---|---|---|---|---|
Good (0–64) | 610 (73.2) | 243 (59.3) | 63 (39.6) | 14 (35.9) |
Acceptable (65–642) | 100 (12.0) | 82 (9.8) | 45 (28.3) | 16 (41.0) |
Torn (> 643) | 123 (14.8) | 85 (20.7) | 51 (32.1) | 9 (23.1) |
LLINs present at all follow-up visits, n = 39 | ||||
Good (0–64) | 34 (87.2) | 29 (74.4) | 19 (48.7) | 14 (35.9) |
Acceptable (65–642) | 4 (10.3) | 6 (15.4) | 13 (33.3) | 16 (41.0) |
Torn (> 643) | 1 (2.6) | 4 (10.3) | 7 (17.9) | 9 (23.1) |
Predictors of physical integrity of LLINs
Variables | Net months observation | Number of torn LLINs | IR/100 NMO (95% CI) | Crude HR (95% CI) | Adjusted HR (95% CI) |
---|---|---|---|---|---|
Gender of head of household | |||||
Male | 5250 | 138 | 2.6 (2.2–3.1) | 1.00 | 1.00 |
Female | 2958 | 60 | 2.0 (1.5–2.5) | 0.8 (0.6–1.0) | 0.8 (0.6–1.3) |
Educational status of head of household (n = 816) | |||||
Illiterate | 4458 | 108 | 2.4 (2.0–2.9) | 1.0 | NA |
Read and write | 822 | 19 | 2.3 (1.4–3.5) | 1.0 (0.6–1.6) | |
Primary | 2010 | 44 | 2.2 (1.5–2.8) | 0.9 (0.6–1.3) | |
Secondary and above | 786 | 18 | 2.3 (1.2–3.3) | 1.0 (0.6–1.6) | |
Wealth status | |||||
Poor | 2826 | 77 | 2.7 (2.1–3.3) | 1.0 | 1.0 |
Middle | 2640 | 62 | 2.3 (1.8–2.9) | 0.9 (0.6–1.2) | 1.0 (0.7–1.5) |
Rich | 2742 | 59 | 2.2 (1.6–2.7) | 0.8 (0.6–1.1) | 0.9 (0.6–1.4) |
Type of bed | |||||
Wooden bedframe | 3786 | 86 | 2.3 (1.8–2.8) | 1.0 | NA |
Stick or iron bedframe | 924 | 23 | 2.5 (1.5–3.5) | 1.1 (0.7–1.8) | |
Mattress (with no bed frame) | 2340 | 56 | 2.4 (1.8–3.0) | 1.1 (0.8–1.5) | |
Mat | 1158 | 33 | 2.8 (1.9–3.8) | 1.2 (0.8–1.9) | |
LLIN hung up | |||||
No | 2358 | 64 | 2.7 (2.0–3.4) | 1.0 | NA |
Yes | 5850 | 134 | 2.3 (1.9–2.7) | 0.8 (0.6–1.1) | |
House has open eave gap (n = 820) | |||||
No | 6888 | 160 | 2.3 (2.0–2.7) | 1.0 | 1.0 |
Yes | 1158 | 38 | 3.3 (2.2–4.3) | 1.4 (0.98–2.0) | 1.0 (0.6–1.4) |
LLIN used last night | |||||
No | 2496 | 75 | 3.0 (2.3–3.7) | 1.0 | 1.0 |
Yes | 5712 | 123 | 2.2 (1.8–2.5) | 0.7 (0.5–0.96)* | 0.7 (0.5–0.96)* |
LLIN ever washed | |||||
No | 4992 | 109 | 2.2 (1.8–2.6) | 1.0 | 1.0 |
Yes | 3216 | 89 | 2.8 (2.2–3.3) | 1.3 (1.0–1.7) | 1.2 (0.9–1.7) |
LLIN was clean | |||||
No | 4440 | 156 | 3.5 (3.0–4.1) | 1.0 | 1.0 |
Yes | 3768 | 42 | 1.1 (0.8–1.5) | 0.3 (0.2–0.4)* | 0.4 (0.3–0.6)* |
Rats present in the house (n = 658) | |||||
No | 3900 | 73 | 1.9 (1.4–2.3) | 1.0 | 1.0 |
Yes | 3186 | 82 | 2.6 (2.0–3.1) | 1.4 (1.02–1.92)* | 1.1 (0.8–1.5) |
Cat present in the house (n = 658) | |||||
No | 3648 | 94 | 2.6 (2.1–3.1) | 1.0 | 1.0 |
Yes | 3438 | 61 | 1.8 (1.3–2.2) | 0.7 (0.5–0.9)* | 0.8 (0.5–1.1) |
Distance from mosquito breeding site (n = 833) (km) | |||||
≤ 1 | 2844 | 51 | 1.8 (1.3–2.3) | 1.0 | 1.0 |
> 1 | 5364 | 147 | 2.7 (2.3–3.1) | 1.5 (1.1–2.1)* | 1.8 (1.2–2.6)* |
Family size (n = 833) | |||||
≤ 5 | 3594 | 90 | 2.5 (2.0–3.0) | 1.0 | NA |
> 5 | 4614 | 108 | 2.3 (1.9–2.8) | 0.9 (0.7–1.2) |
Functional survival
Predictors of functional survivorship of LLINs
Variable | Net month observation | Number of lost LLINs | IR/100 NMO (95% CI) | Crude HR (95% CI) | Adjusted HR (95% CI) |
---|---|---|---|---|---|
Gender of head of household (n = 1193) | |||||
Male | 9930 | 660 | 6.6 (6.1–7.2) | 1.0 | NA |
Female | 5262 | 333 | 6.3 (5.6–7.0) | 1.0 (0.8–1.1) | |
Educational status of head of household (n = 1170) | |||||
Illiterate | 8472 | 567 | 6.7 (6.1–7.2) | 1.0 | 1.0 |
Read and write | 1554 | 99 | 6.4 (5.1–7.6) | 0.9 (0.7–1.1) | 0.9 (0.7–1.3) |
Primary | 3606 | 227 | 6.3 (5.5–7.1) | 0.9 (0.8–1.1) | 1.0 (0.9–1.3) |
Secondary and above | 1308 | 79 | 6.0 (4.7–7.4) | 0.9 (0.7–1.1) | 0.9 (0.7–1.2) |
Wealth status (n = 1184) | |||||
Poor | 5244 | 363 | 6.9 (6.2–7.6) | 1.0 | 1.0 |
Middle | 4872 | 312 | 6.4 (5.7–7.1) | 0.9 (0.8–1.0) | 1.0 (0.8–1.2) |
Rich | 4968 | 312 | 6.3 (5.6–7.0) | 0.9 (0.8–1.0) | 0.9 (0.8–1.2) |
Open eave (n = 1176) | |||||
No | 12,480 | 819 | 6. 6 (6.1–7.0) | 1.0 | NA |
Yes | 2460 | 166 | 6.7 (5.7–7.8) | 1.0 (0.9–1.2) | |
LLIN used last night (n = 833) | |||||
No | 3468 | 237 | 6.8 (6.0–7.7) | 1.0 | 1.0 |
Yes | 7746 | 459 | 5.9 (5.4–6.5) | 0.8 (0.7–0.97)* | 1.0 (0.7–1.0) |
LLIN ever washed (n = 833) | |||||
No | 6876 | 423 | 6.2 (5.6–6.7) | 1.0 | |
Yes | 4338 | 273 | 6.3 (5.5–7.0) | 1.0 (0.9–1.2) | NA |
LLIN was clean (n = 833) | |||||
No | 6012 | 418 | 7.0 (6.3–7.6) | 1.0 | 1.0 |
Yes | 5202 | 278 | 5.3 (4.7–6.0) | 0.7 (0.6–0.8)* | 0.8 (0.6–0.9) * |
Rats present in the house (n = 858) | |||||
No | 6462 | 382 | 5.9 (5.3–6.5) | 1.0 | 1.0 |
Yes | 5316 | 334 | 6.3 (5.6–7.0) | 1.1 (1.0–1.3) | 1.1 (0.9–1.3) |
Cat present in the house (n = 858) | |||||
No | 6102 | 378 | 6.2 (5.6–6.8) | 1.0 | |
Yes | 5676 | 338 | 6.0 (5.3–6.6) | 1.0 (0.8–1.1) | NA |
Distance from mosquito breeding site (n = 1193) (km) | |||||
≤ 1 | 5058 | 311 | 6.1 (5.5–6.8) | 1.0 | 1.0 |
> 1 | 10,134 | 682 | 6.7 (6.2–7.2) | 1.2 (1.1–1.3)* | 1.3 (1.1–1.6)* |
Household population size (n = 1193) | |||||
≤ 5 | 6264 | 392 | 6.3 (5.6–6.9) | 1.0 | 1.0 |
> 5 | 8928 | 601 | 6.7 (6.2–7.3) | 1.1 (1.0–1.3) | 1.1 (0.9–1.3) |
Bio-efficacy
Survey (months) | Number of LLINs | 60-min KD GM (95% CI) | 24-h mortality GM (95% CI) |
---|---|---|---|
6 | 30 | 94.1 (87.1–100) | 81.1 (67.7–97.0) |
12 | 30 | 99.9 (99.7–100) | 89.5 (87.2–91.8) |
18 | 30 | 93.9 (90.0–98.1) | 76.6 (71.0–82.6) |
24 | 30 | 94.1 (91.3–97.1) | 69.4 (59.4–80.9) |
Variable | Between months | Mean difference (95% CI)a | P value |
---|---|---|---|
Knockdown | 12 and 18 | 5.4 (0.4–10.4) | 0.029 |
12 and 24 | 5.5 (1.7–9.3) | 0.002 | |
Mortality | 12 and 18 | 11.7 (4.1–19.2) | 0.001 |
12 and 24 | 15.4 (3.1–27.8) | 0.008 |
Age of LLINs (months) | Number evaluated | n (%), 95% CI |
---|---|---|
6 | 30 | 27 (90.0), 72.5–96.8 |
12 | 30 | 30 (100) |
18 | 30 | 25 (83.3), 65.1–93.1 |
24 | 30 | 24 (80.0), 61.5–90.9 |