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...

Spatial and temporal comparison of selected cancers in dogs and humans, Michigan, USA, 1964-1994.

Our aim was to investigate the geographic and time distributions of some biologically similar neoplasms in dogs and humans living in Michigan, USA, between 1964 and 1994. Our objective was to describe and compare the patterns of cancer in the two species while assessing the strength and dependence of those patterns. In this retrospective, registry-based study, histologically confirmed incident human and canine cancer cases were mapped, and second-order (K function) spatial analysis and one-dimensional nearest neighbor temporal analysis were performed on residence addresses and dates of hospital discharge/diagnosis. Included in the study were all 528 incident cases of canine lymphosarcoma, mammary adenocarcinoma, melanoma and spindle-cell sarcomas diagnosed at a veterinary teaching hospital between 1964 and 1994 having residence addresses in Ingham, Oakland, and Wayne Counties; and a stratified random sample of 913 incident human cases of comparable cancers diagnosed during the same time period from the same counties. Results suggest that processes determining spatial aggregation of cases in dogs and humans were not independent of each other, did not act uniformly over different geographic areas, operated at spatial scales <2000 m regardless of species, and tend to act upon dogs more strongly at shorter distances than on humans. Little evidence of interspecies concurrence of temporal clustering was found.

Spatial and temporal distribution of selected canine cancers in Michigan, USA, 1964-1994.

Although rates are commonly used to compare regional disease occurrence, rate-independent methods might also be useful in circumstances where geographic occurrence of a disease is known, but calculation of disease rates is not feasible. This is frequently the case for diseases in companion animals, where accurate enumeration of populations-at-risk is often arduous. This study had two objectives: to demonstrate a rate-independent method for investigating disease aggregation in companion animals; and, to assess the spatial and temporal clustering of canine cases of four cancers that are biologically similar in dogs and humans. Geographic information systems and point-pattern analysis were used to assess the spatial and temporal clustering of incident cases of four types of canine cancer in three counties in Michigan between 1964 and 1994, and to generate hypotheses concerning disease aggregation. Significant (P < or = 0.01) spatial clustering was found that varied by county and cancer type. No definitive temporal patterns could be deduced from a temporal analysis of the cases of canine cancer in this study. These results demonstrate distance-based methods for assessing clustering of disease, and suggest that processes determining the aggregation of canine cancer cases do not act in a spatially uniform manner.

Exploratory space-time analysis of reported dengue cases during an outbreak in Florida, Puerto Rico, 1991-1992.

The spatial and temporal distributions of dengue cases reported during a 1991-1992 outbreak in Florida, Puerto Rico (population = 8,689), were studied by using a Geographic Information System. A total of 377 dengue cases were identified from a laboratory-based dengue surveillance system and georeferenced by their residential addresses on digital zoning and U.S. Geological Survey topographic maps. Weekly case maps were generated for the period between June and December 1991, when 94.2% of the dengue cases were reported. The temporal evolution of the epidemic was rapid, affecting a wide geographic area within seven weeks of the first reported cases of the season. Dengue cases were reported in 217 houses; of these 56 (25.8%) had between two and six reported cases. K-function analysis was used to characterize the spatial clustering patterns for all reported dengue cases (laboratory-positive and indeterminate) and laboratory-positive cases alone, while the Barton and David and Knox tests were used to characterize spatio-temporal attributes of dengue cases reported during the 1991-1992 outbreak. For both sets of data significant case clustering was identified within individual households over short periods of time (three days or less), but in general, the cases had spatial pattern characteristics much like the population pattern as a whole. The rapid temporal and spatial progress of the disease within the community suggests that control measures should be applied to the entire municipality, rather than to the areas immediately surrounding houses of reported cases. The potential for incorporating Geographic Information System technologies into a dengue surveillance system and the limitations of using surveillance data for spatial studies are discussed.

PIP: Through use of the Geographic Information System (GIS), the spatial and temporal distributions of dengue cases reported during a 1990-91 outbreak in Florida, Puerto Rico, were reviewed. The GIS, a computer system that can store, assemble, manipulate, and analyze geographically referenced material, offers a new approach to the study of disease patterns. A total of 377 dengue cases were identified from a laboratory-based dengue surveillance system and georeferenced by their residential addresses on digital zoning and US Geological Survey topographic maps. Weekly case maps were generated for the period June-December 1991, when 94.2% of dengue cases were reported. The epidemic's temporal evolution was rapid, affecting a wide geographic region within 7 weeks of the first reported cases of the season. Cases were reported in 217 houses, 56 (25.8%) of which had 2-6 cases each. Both K-function analysis, and the Barton and David-Knox tests, revealed significant case clustering within individual households over a period of 3 days or less. In general, however, cases had spatial pattern characteristics similar to the population pattern as a whole. The rapid spatial and temporal progress of dengue cases within the community suggests that vector control measures (e.g., source reduction) should be applied to the entire municipality, rather than to the areas immediately surrounding houses of reported cases.

Economic heterogeneity within large metropolitan areas.

PIP: In recent years, research has indicated a trend in the US for the distribution of income to become bimodal, with movement away from a dominant middle class and toward more people being in the upper or lower ends of the income scale. With this trend, an analysis of municipalities would be expected to show frequency distributions for various economic variables that would have widened, become more skewed, and become flattened or U-shaped. Additionally, the mode of distribution would be expected to move toward the lower income end. An analysis of individuals within the rich and poor communities would be expected to show frequency distributions that have narrowed. This study tested the above expectations. The usual measures of skewness and peakedness were used for data analyses, as well as a modified Pearson place. The metropolitan areas sampled were Atlanta, Boston, Chicago, Dallas, Detroit, Los Angles, and Washington, DC. Changes were looked for in comparing per capita income figures from the US Census for each municipality in the metropolitan areas in 1969,1979, and 1983. For individual municipalities, a sample of 30 Chicago suburbs was used to show income distribution. Results of per capita income in metropolitan areas (except Dallas) for 1969-1979 showed that middle income communities became more dominant, not less; therefore, the poorer communities became richer. The results for 1979-1983 showed that the trend came to a halt. For individual income results, a trend toward greater homogeneity in the 1970s came to a halt in the 1980s and began to reverse itself. For individual municipalities, the larger ones were more heterogeneous. Additionally, those with greater population increases were more homogeneous in income, and those with the highest increases in income tended to be moving toward more homogeneity. The poor communities, therefore, were more income-heterogeneous. A bimodal income distribution does not exist, but some metropolitan areas are moving in that direction.^ieng