LLIN Durability Monitoring Background and Objectives.
Transcript of LLIN Durability Monitoring Background and Objectives.
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LLIN Durability Monitoring
Background and Objectives
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Overview
Some background on malaria prevention with LLIN
Why is LLIN durability important? What is durability? How to measure it? Why this study?
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Parasite Vector
Host
Environment
Determinants of Malaria
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Options for Vector Control
• The objective of integrated vector management is to reduce survival of the vector population to a degree that transmission is significantly reduced or interrupted
Environmental Management
Larval Control
Adult mosquito Control
Protection from bites
Indoor Residual Spraying
Insecticide Treated Net
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The principle of ITNs
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The LLIN Technology Conventional ITN need re-treatment Very difficult to maintain high re-treatment levels The technology of long-lasting insecticidal nets (LLIN or LN) has
made re-treatment redundant LLIN made ITN suitable for mass application
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Polyester Polyethylene
The netting materials for LLIN
Polypropylene
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Mosquito exposed to insecticide
The working principle of polyester LLIN
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Insecticide lost through washing
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Insecticide lost through washing
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Insecticide lost through washing
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Insecticide lost through washing
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Regeneration after washing
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Gradual depletion of insecticide
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Gradual depletion of insecticide
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Gradual depletion of insecticide
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Gradual depletion of insecticide
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Current LLIN Brands Net/Brand Material Denier (fiber
strength)Mesh
holes/sqr inchInsecticide mg/sqr m
Olyset Polyethylene 150 75 Permethrin1000
Duranet MAGNet Royal Sentry MiraNet
Polyethylene 145 132 Alphacypermethrin260
Netprotect IconLife PandaNet 2.0 Polyethylene 100-115 136 & 200 Deltamethrin
63
Permanet 2.0 Yorkool Yahe
Polyester 75, 100 156-177Deltamethrin
55
Interceptor SafeNet Polyester 75, 100 156-177
Alphacypermethrin200
Dawa Plus 2.0 Polyester 75, 100, 150 156-177Deltamethrin
80
LifeNet Polypropylene 110 156 Deltamethrin340
Olyset Plus Polyethylene 150 80Permethrin and PBO
PermaNet 3.0 Polyester (sides) & polyethylene (roof) 75, 100 156-177
Deltamethrin and PBO
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Current LLIN Brands Given high loading doses in newer LLIN
insecticide effect expected to last > 3yrs
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How to identify an LLIN Since you cannot see the insecticide, the only
way to identify an LLIN is by its brand label !!!!
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Net and LLIN durability
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Stress on net varies
• Between regions (environment)• Between households (socio-economic)• Between nets within household• Over the lifespan of the net
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What is LLIN durability?
Net durability How long does the LLIN remain available to be
used for sleeping under Retention/attrition Physical condition (integrity)
Insecticidal protection When does an LLIN lose its ability to protect
beyond just the net given the physical condition
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Why is LLIN durability important?
For many years the question “how long does an ITN last” was not relevant and therefore not asked
With the intensified scale-up the questions on how many nets will be needed to sustain success becomes critical
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Why is LLIN durability important?
Potential savings from better LLIN
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Net is gone
HH has net
Are the nets still there?
Time
loss function
Attrition RateProportion Lost
Retention RateProportion Retained
Retention - Attrition
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Net Attrition-Reasons for Net LossKenya, 30 Months Post-Distribution
Destroyed-Burned by FireDiscarded-Too Damaged
Discarded-Not killing mosquitoes
Sold/Given Away
Unable to Trace Net
Other
Lost/Stolen
Moved/Taken from House
Source: John Gimnig CDC
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Attritiono Reason for loss from post-campaign and retrospective
durability surveys in Nigeria (N=780)
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Net is gone
HH has net
Are surviving nets still OK?
Time
Surviving nets
Physical Condition
Discarded nets not included
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How to measure integrity
• Cross-sectional surveys– Works initially– But if nets are discarded at a certain state of
destruction a steady state will be reached• Longitudinal study– Preferable approach– But more time consuming
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How to assess net condition
• Classifying and counting holes– Ideally done in lab on frame– But not feasible in large field surveys as part of
comprehensive questionnaires– Need something more robust
• Currently recommended classes– Size 1: 0.5-2cm (thumb)– Size 2: 2-10 cm (fist)– Size 3: 10-25cm (head)– Size 4: >25cm (larger than head)
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How to get composite hole index
• Need one overall measure of integrity• Weighted summary of holes of different sizes• Proportionate Hole Index– Approximate measure of total hole surface– Standardized approach
1.6 cm²36 cm²
306 cm²
1 23 196
900 cm²
576x # size 1 + x # size 2 + x # size 3 x # size 4
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How to analyze hole index data
• Need to categorize nets– Good– Damaged– Torn
Serviceable
• Current cut-offs recommended by WHO– Good= <64 pHI or < 100cm² holes– Max 2 size 2, none size 3– Torn= > 642 pHI or > ~0.1m² holes– More than 4 size 3 or 2 size 4– Serviceable: <643 pHI
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East Chad (MENTOR)
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How to combine attrition and integrityD
istrib
uted
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Still
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Lost
Still
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Goo d
Dam
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From distribution list or recall
Durability or survival rate
Exclude nets given away or stolen (no outcome)
Denominator for durability
(survival rate)
Survey after time X
Nets thrown away, distroyed or used
otherwise
Physical assessment of surviving nets
serv
icab
le
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How to combine attrition and integrity
Durability =# of nets still there and fit for use at time x
# of nets originally received and not given away
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Plot survival outcome
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Estimating median survivalo From at least 2 points of which the lowest should be 85%
or lower
Time point
Time in years
Functional survival
Median survival using last two data points
(95% CI)
1 1.0 93.3% n.a.2 1.7 83.4% 4.1 (3.7 to 4.5)3 2.4 68.2% 3.2 (3.0 to 3.5)4 3.1 53.2% 3.3 (3.0 to 3.5)5 4.3 31.6% 3.3 (3.0 to 3.6)
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Why this study?
PMI guidance now includes routine durability monitoring
Collect LLIN durability data comparing different eco-geographical zones
Explore the potential of BCC on care & repair to increase durability
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Durability - Survival
Zamfara Nasarawa Cross River
Median5.2 yrs
95% CI 4.8-5.8
Median2.7 yrs
95% CI 2.5-2.8
Median4.4 yrs
95% CI 3.6-5.5
39.5% 72.2%74.6%
40
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Impact: Positive attitude on behavior
• Attitudes towards care and repair vs. net integrity
Good Torn
41
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Photo courtesy of Caroline Vanderick/SuNMaP
Thank You