Evaluation of a sampling methodology for rapid assessment of Aedes aegypti infestation levels in Iquitos, Peru.

An epidemic of dengue during 2001 in Northwestern Peru reemphasized the need for efficient, accurate, and economical vector surveillance. Between November 1998 and January 1999, we carried out extensive entomological surveys in two neighborhoods of approximately 600 contiguous houses located in the Amazonian city of Iquitos, providing a unique opportunity to evaluate the Aedes aegypti (L.) rapid assessment survey strategy. Based on Pan American Health Organization recommendations, this strategy is used by the Peruvian Ministry of Health (MOH). In our analysis all household locations, including closed and unoccupied houses, were georeferenced and displayed in a geographic information system, which facilitated simulations of MOH surveys based on hypothetical systematic sampling transects. Larval, pupal, and adult mosquito indices were calculated for each simulation (n = 10) and compared with the indices calculated from the complete data set (n = 4). The range of indices calculated from simulations was moderately high, but included actual indices. For example, simulation ranges for house indices (HI, percentage of infested houses from complete survey) were 38-56% (45%), 36-42% (38%), 21-34% (30%), and 13-33% (27%) in four surveys. HI, Breteau index, pupae per hectare, adult index, and adults per hectare were more robust entomological indicators (coefficient of variation [CV]/mean = 0.1-2.9) than the container index, pupae per person, pupae per house, adults per person, and adults per house (CV/mean >20). Our results demonstrate that the MOH's Ae. aegypti risk assessment program provides reasonable estimates of indices based on samples from every house. However, it is critical that future studies investigate the association of these indices with rates of virus transmission to determine whether sampling variability will negatively impact the application of indices in a public health context.

Evaluation of a sampling methodology for the Rapid Assessment of Aedes aegypti infestation levels in Iquitos, Perú

An epidemic of dengue during 2001 in Northwestern Peru has re-emphasized the need for efficient, accurate, and economical vector surveillance methods. Between November 1998 and January 1999 we carried out extensive entomological surveys in two neighborhoods (Maynas and Tupac) of 600 contiguous houses (14-20 blocks) each located in the Amazonian city of Iquitos, which has provided a unique opportunity to evaluate the Aedes aegypti rapid assessment survey strategy. This strategy is based on PAHO recommendations employed by the Peruvian Ministry of Health (MOH). All household locations from 4 surveys (2/neighborhood), including closed and unoccupied houses were georeferenced and displayed in a Geographic Information System (GIS), facilitating simulations of 10 MOH surveys based on hypothetical systematic sampling transects for 3 work groups (15-25 houses per group starting from randomly selected blocks). Larval, pupal and adult mosquito indices were calculated for each simulation and compared to the indices calculated from the complete data set. Infestation rates were highest in Maynas where House Indices (HI: proportion of houses positive for larvae) were 45% and 38% in surveys 1 and 2, respectively. In Tupac Amaru the HI was 30% in survey 1 and 27% survey 2. The observed range in simulated House indices in Maynas survey 1 and 2 were 38-56% and 36-42%; whereas in Tupac they were 21-34% and 13-33%. Index stability was evaluated by comparing the coefficient of variation to the mean of the simulation results. HI, Breteau index, pupae/ha, adult index, and adults/ha were more robust entomological indicators (CV/mean=0.1-2.9), than the container index, pupae/person, pupae/house, adults/person, and adults/house (CV/mean>20). Results demonstrate that the MOH's Aedes aegypti risk assessment program provides reasonable estimates of actual indices; however, the further understanding of the association of these indices with rates of virus transmission...

Comparativo de metodologías para el levantamiento del Índice Aédico en la localidad Pampa Huasa Huasi. Dirección de Salud Junín / Comparison of methodologies for the lifting of the index Aédico in the town Pampa Huasa Huasi. Direccion de Salud Junin

Objetivo: Comparar estadísticamente las metodologías que se utilizan en la determinación del Índice Aédico en una área infestada. Material y métodos: El área seleccionada fue la localidad de Pampa de Huasa Huasi (502 viviendas) del Distrito de Chanchamayo, Provincia de Chanchamayo, Junín. El trabajo de campo se inicio con el levantamiento del índice aédico a través de la inspección del 100% de viviendas. Esta metodología se tomó como referencia para comparar los resultados de las otras metodologías empleadas. Se continuo con la metodología del 33% (171 viviendas), la metodología de muestra probabilística (98 viviendas) y finalmente la metodología utilizando las Tablas de OPS/OMS (84 viviendas). Resultados: Con la metodología del censo o 100% de viviendas inspeccionadas, el Índice de Infestación Aédica (IIA) fue de 16.1%, el Índice de Recipiente (IR) 9.5% y el Índice de Breteau (IB) de 26%. Con la metodología del 33% de inspección de viviendas, el IIA fue de 16.3%, el IR de 8.4% y el IB de 25.7%. Con muestra probabilística, el IIA fue de 19.3%, IR de 9.4% y el IB de 25.5%. Utilizando tablas de OPS/OMS, el IIA fue de 10.7%, el IR de 8.5% y el IB de 16.8%. Conclusiones: Los resultados obtenidos con las metodologías del 33%, muestreo probabilístico y tablas de OPS/OMS no son significativamente diferentes. Se recomienda trabajar con muestras estadísticas para las actividades de vigilancia entomológica de Aedes aegypti a nivel nacional.

Objective: To compare statistically the methodologies employed in the Aedic Index asses in an infested area. Methods: The chosen area was the community Pampa Huasa Huasi (502 houses), District Chanchamayo, Province Chanchamayo, Junín. The survey started with the Aedic Index evaluation by the inspection of the 100% of houses. This methodology was taken as reference to compare the results of the others methodologies employed. The next was the 33% methodology (171 houses), the probabilistic sample methodology (98 houses) and finally the PAHO/WHO schedules methodology (84 houses). Results: With the census or 100% houses methodology, the Aedic Infestation Index (AII) was 16.1%, the Recipient Index (RI) 9.5% and the Breteau Index (BI) 26%. With the 33% methodology, the AII was 16.3%, the RI was 8.4 and the BI was 25.7%. With the probabilistic sample, the AII was 19.3%, the RI was 9.4% and the BI was 25.5%. Employing the PAHO/WHO schedules, the AII was 10.7%, the RI was 8.5% and the BI was 16.8%. Conclusions: The results obtained with the 33% methodology, probabilistic sample and PAHO/WHO schedules are not statistically differents. It is recommended to work with statistic samples for the entomologic surveillance of Aedes aegypti.