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Field durability of the same type of long-lasting insecticidal net varies between regions in Nigeria due to differences in household behaviour and living conditions.

Kilian A, Koenker H, Obi E, Selby RA, Fotheringham M, Lynch M - Malar. J. (2015)

Bottom Line: The proportion of surviving nets in serviceable condition differed dramatically, however, resulting in an estimated median net survival of 3.0 years in Nasarawa, 4.5 years in Cross River and 4.7 years in Zamfara.Although repairs on damaged nets increased from around 10% at baseline to 21-38% after three years, the average pHI value for each of the four hole size categories did not differ between repaired and unrepaired nets.Third, repair does not seem to measurably improve net condition and focus should, therefore, be on improving preventive behaviour.

View Article: PubMed Central - PubMed

Affiliation: Tropical Health LLP, Montagut, Spain. albert@trophealth.com.

ABSTRACT

Background: With the recent publication of WHO-recommended methods to estimate net survival, comparative analyses from different areas have now become possible. With this in mind, a study was undertaken in Nigeria to compare the performance of a specific long-lasting insecticidal net (LLIN) product in three socio-ecologically different areas. In addition, the objective was to assess the feasibility of a retrospective study design for durability.

Methods: In three states, Zamfara in the north, Nasarawa in the centre and Cross River in the south, four local government areas were selected one year after mass distribution of 100-denier polyester LLINs. From a representative sample of 300 households per site that had received campaign nets, an assessment of net survival was made based on rate of loss of nets and the physical condition of surviving nets measured by the proportionate hole index (pHI). Surveys were repeated after two and three years.

Results: Over the three-year period 98% of the targeted sample size of 3,720 households was obtained and 94% of the 5,669 campaign nets found were assessed for damage. With increasing time since distribution, recall of having received campaign nets dropped by 11-22% and only 31-87% of nets actually lost were reported. Using a recall bias adjustment, attrition rates were fairly similar in all three sites. The proportion of surviving nets in serviceable condition differed dramatically, however, resulting in an estimated median net survival of 3.0 years in Nasarawa, 4.5 years in Cross River and 4.7 years in Zamfara. Although repairs on damaged nets increased from around 10% at baseline to 21-38% after three years, the average pHI value for each of the four hole size categories did not differ between repaired and unrepaired nets.

Conclusions: First, the differences observed in net survival are driven by living conditions and household behaviours and not the LLIN material. Second, recall bias in a retrospective durability study can be significant and while adjustments can be made, enough uncertainty remains that prospective studies on durability are preferable wherever possible. Third, repair does not seem to measurably improve net condition and focus should, therefore, be on improving preventive behaviour.

No MeSH data available.


Related in: MedlinePlus

Survival in functional condition of campaign nets (100-denier polyester LLIN) up to three years after distribution in comparison to hypothetical survival curves of defined median survival. Solid lines = recall adjusted estimates; dashed line = crude estimates; horizontal dotted line = median survival; vertical arrows indicate where the functional survival curves reach or are projected to reach the median.
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Fig2: Survival in functional condition of campaign nets (100-denier polyester LLIN) up to three years after distribution in comparison to hypothetical survival curves of defined median survival. Solid lines = recall adjusted estimates; dashed line = crude estimates; horizontal dotted line = median survival; vertical arrows indicate where the functional survival curves reach or are projected to reach the median.

Mentions: The resulting, estimated, functional survival of campaign nets is shown in Table 3 and Figure 2. There was a striking difference between the crude and recall-adjusted estimates of functional net survival especially in Zamfara and Cross River with 15.2 and 18.4 percentage-point differences, respectively, after three years. In Nasarawa the discrepancy was not quite as high with an 11.2 percentage-point difference but here the overall survival estimate was more than 30 percentage points lower than at the other two sites reaching only 42% at the third survey round.Table 3


Field durability of the same type of long-lasting insecticidal net varies between regions in Nigeria due to differences in household behaviour and living conditions.

Kilian A, Koenker H, Obi E, Selby RA, Fotheringham M, Lynch M - Malar. J. (2015)

Survival in functional condition of campaign nets (100-denier polyester LLIN) up to three years after distribution in comparison to hypothetical survival curves of defined median survival. Solid lines = recall adjusted estimates; dashed line = crude estimates; horizontal dotted line = median survival; vertical arrows indicate where the functional survival curves reach or are projected to reach the median.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4376338&req=5

Fig2: Survival in functional condition of campaign nets (100-denier polyester LLIN) up to three years after distribution in comparison to hypothetical survival curves of defined median survival. Solid lines = recall adjusted estimates; dashed line = crude estimates; horizontal dotted line = median survival; vertical arrows indicate where the functional survival curves reach or are projected to reach the median.
Mentions: The resulting, estimated, functional survival of campaign nets is shown in Table 3 and Figure 2. There was a striking difference between the crude and recall-adjusted estimates of functional net survival especially in Zamfara and Cross River with 15.2 and 18.4 percentage-point differences, respectively, after three years. In Nasarawa the discrepancy was not quite as high with an 11.2 percentage-point difference but here the overall survival estimate was more than 30 percentage points lower than at the other two sites reaching only 42% at the third survey round.Table 3

Bottom Line: The proportion of surviving nets in serviceable condition differed dramatically, however, resulting in an estimated median net survival of 3.0 years in Nasarawa, 4.5 years in Cross River and 4.7 years in Zamfara.Although repairs on damaged nets increased from around 10% at baseline to 21-38% after three years, the average pHI value for each of the four hole size categories did not differ between repaired and unrepaired nets.Third, repair does not seem to measurably improve net condition and focus should, therefore, be on improving preventive behaviour.

View Article: PubMed Central - PubMed

Affiliation: Tropical Health LLP, Montagut, Spain. albert@trophealth.com.

ABSTRACT

Background: With the recent publication of WHO-recommended methods to estimate net survival, comparative analyses from different areas have now become possible. With this in mind, a study was undertaken in Nigeria to compare the performance of a specific long-lasting insecticidal net (LLIN) product in three socio-ecologically different areas. In addition, the objective was to assess the feasibility of a retrospective study design for durability.

Methods: In three states, Zamfara in the north, Nasarawa in the centre and Cross River in the south, four local government areas were selected one year after mass distribution of 100-denier polyester LLINs. From a representative sample of 300 households per site that had received campaign nets, an assessment of net survival was made based on rate of loss of nets and the physical condition of surviving nets measured by the proportionate hole index (pHI). Surveys were repeated after two and three years.

Results: Over the three-year period 98% of the targeted sample size of 3,720 households was obtained and 94% of the 5,669 campaign nets found were assessed for damage. With increasing time since distribution, recall of having received campaign nets dropped by 11-22% and only 31-87% of nets actually lost were reported. Using a recall bias adjustment, attrition rates were fairly similar in all three sites. The proportion of surviving nets in serviceable condition differed dramatically, however, resulting in an estimated median net survival of 3.0 years in Nasarawa, 4.5 years in Cross River and 4.7 years in Zamfara. Although repairs on damaged nets increased from around 10% at baseline to 21-38% after three years, the average pHI value for each of the four hole size categories did not differ between repaired and unrepaired nets.

Conclusions: First, the differences observed in net survival are driven by living conditions and household behaviours and not the LLIN material. Second, recall bias in a retrospective durability study can be significant and while adjustments can be made, enough uncertainty remains that prospective studies on durability are preferable wherever possible. Third, repair does not seem to measurably improve net condition and focus should, therefore, be on improving preventive behaviour.

No MeSH data available.


Related in: MedlinePlus