during 20112013 , in the city of acapulco in guerrero state , mexico ( figure 1 ) , an area of consistently high dengue transmission ( http://www.epidemiologia.salud.gob.mx/dgae/panodengue/intd_dengue.html ) , we investigated the effect on vector infestations of permanently mounted , insecticide - treated screens fitted to doors and windows of residential houses . the screens ( duranet , clarke mosquito control , roselle , il , usa ) were made of 0.55% wt / wt -cypermethrin  treated nonflammable polyethylene netting ( 145 denier ; mesh  =  132 holes / in ) ; the design is approved by the world health organization ( who ) pesticide evaluation scheme ( http://www.who.int/whopes/en/ ) . area of study of long - lasting insecticide - treated screens in acapulco , mexico , march 2011march 2013 . a ) locations of clusters in the neighborhoods of ciudad renacimiento and zapata , showing areas with ( red ) and without ( blue ) screens . insets show location of study area ( black box ) in acapulco and guerrero state ( black shading ) in mexico . b ) photographs of screens mounted on aluminum frames and fixed to windows and external doors of treated houses in 2012 . we used a cluster - randomized sampling design constructed on the basis of earlier studies ( 46,11 ) to select 20 clusters ( 10 treatment , 10 control ; 100 households / cluster ) from a possible 30 clusters by using digital maps ( google earth software ; google inc . sample size was determined by using a 2-level hierarchical model to achieve 80% power at a 5% level of significance . thus , for a negative binomial distribution with a dispersion coefficient of 0.02 and intracluster coefficient of 0.05 , a minimum of 8.9 clusters / arm were required . written informed consent was obtained from participating households ; the who ethical review committee ( who reference no . participating households in the treatment arm were instructed on llis maintenance during installation ( april  december 2012 ) . five entomologic surveys of randomly selected houses were conducted : before intervention ( march 2011 , september 2011 , march 2012 ) and at 5 and 12 months after intervention ( september 2012 , march 2013 ; wet and dry seasons , respectively ) . before intervention , 32 houses per cluster were sampled at each survey ; after intervention , 210 houses from treated clusters and 302 from control clusters were sampled in september 2012 and 311 houses from treated and 320 from control clusters in march 2013 . indoor resting adult mosquitoes were collected by using modified cdc backpack aspirators ( john w. hock co. , gainesville , fl , usa ) from all houses in a cluster on the same day during 9 am3 pm . aegypti mosquitoes ( the only aedes species found ) were calculated to quantify house infestation ( percent of all houses positive ) and infestation density ( numbers per infested house ) for all mosquitoes , all females , all blood - fed females , and males . for presence  absence data , we performed logistic regression models with a single predictor variable identifying houses with llis and control houses ( coded as 1 and 0 , respectively ) and accounting for each house membership in a given sampling cluster ( cluster - robust se calculation ) . odds ratios ( ors ) and 95% cis indicating the effect of llis on each entomologic indicator were calculated . overdispersed index data were compared between arms by using the mann - whitney u test . the effect of treatment on each metric was analyzed by negative - binomial regression using , as with the logistic models , treatment as the sole predictor variable ( 1 and 0 coding ) . negative binomial models also accounted for membership of a house in a sampling cluster ( cluster - robust se calculation ) . ors and incidence rate ratios ( irrs ) were calculated with 95% cis ; significance was set at p<0.05 . analyses were performed by using stata 12.0 ( statacorp , college station , tx , usa ) . before intervention , indices were similar for both study arms on all sampling dates . house infestation rates ( figure 2 , panels a d ) and mosquito densities ( figure 2 , panels e  h ) followed seasonal patterns ( 2-sample wilcoxon rank - sum test for all treatment  control comparisons , |z|<1.0 ; p>0.1 ) . at 5 months postintervention , aegypti adult female mosquitoes ( or  0.38 , 95% ci 0.210.69 ) , blood - fed females ( or  0.36 , 95% ci 0.210.60 ) , and males ( or  0.39 , 95% ci 0.190.77 ) . a significant effect was still seen at 12 months for adult females ( or  0.41 , 95% ci 0.250.68 ) and males ( or  0.41 , 95% ci 0.270.64 ) but not for blood - fed females ( or  0.51 , 95% ci 0.241.05 ) . aegypti mosquitoes found in treated than in control houses : adult females at 5 ( irr  0.37 , 95% ci 0.270.49 ) and 12 ( irr  0.40 , 95% ci 0.230.70 ) months postintervention , males at 5 ( irr  0.39 , 95% ci 0.280.54 ) and 12 ( irr  =  0.49 , 95%ci 0.330.72 ) months postintervention , and blood - fed females at 5 ( irr  0.32 , 95% ci 0.230.45 ) but not 12 ( irr  0.49 , 95% ci 0.231.05 ) months postintervention . infestation indices for adult aedes aegypti mosquitoes in intervention ( solid lines ) and control ( dashed lines ) households before and after intervention in acapulco , mexico , as measured during dry ( march ) and wet ( august  september ) season cross - sectional surveys , 20112013 . a d ) vector prevalence : percentage of houses positive for a ) all adults ; b ) all females ; c ) blood - fed females ; d ) males . e  h ) vector density : mean number per infested house for e ) all adults ; f ) all females ; g ) blood - fed females ; h ) males . asterisks ( * ) denote dates when the index was significantly different between treated and control groups . a comparison of wet season data from treatment houses before ( august 2011 ) and after ( september 2012 ) intervention showed that significantly fewer females and blood - fed females were found postintervention ( wilcoxon matched pairs w  =  30706 , z  =  3.717 , and w  =  20706 , z  =  3.146 ; p<0.05 for both comparisons ) . however , the number of male mosquitoes did not change significantly ( w  =  20706 , z  =  1.385 ; p>0.05 ) . at 5 months postintervention , fewer llis - treated houses ( 33% ) than control houses ( 56% ) remained infested with female ae . lower numbers of female mosquitoes were also found per infested house ( 0.54  0.9 ) than per control house ( 1.39  2.0 ) ; this effect was still detectable at 12 months postintervention ( 18% , 0.3  0.8 , vs. 35% , 0.7  1.4 ) . in our study , the entomologic effect of llis was greater than that detected in a recent study of deltamethrin - treated window curtains ( 12 ) , in which a 27% reduction of adult ae . other studies of insecticide - treated curtains in latin america have reported entomologic effects by using immature stage indicators alone ( 4,5,7 ) . whether these reductions were sufficient to affect dengue transmission is unknown , and the overall effect on dengue infections remains to be evaluated . although resistance to -cypermethrin has yet to be reported in guerrero , high frequencies of mutations in the voltage - gated sodium channel gene , which is associated with pyrethroid resistance in ae . if insecticide resistance began to reduce the efficacy of the method we describe , the screens could be treated with different insecticide classes . we found the use of llis was a popular intervention , and perceived efficacy was reinforced by a reduction in other domestic pests ( figure 1 ) ( 14 ) . the likely effects on other peridomestic disease vectors could promote increased adoption of the intervention with additional cost benefits . the polyethylene netting was durable on windows ; it was often damaged on the lower sections of doors ( 14 ) but readily repaired by reinforcement with metal mesh . dengue vector control programs using house screens are ongoing in selected cities in mexico and brazil . stakeholders in other countries may also consider evaluating this novel approach for dengue vector control .