general population, identify risk factors, and investigate the rodent species implicated in hantavirus transmission in Yuto. Material and Methods Study Area Yuto is located in the Ledesma Department, in the northeastern portion of Jujuy Province (23° 38′ S, 64° 28′ W). General topography is determined by the outlying spurs of the Andes range, and the area is covered by dense subtropical vegetation. The easternmost part of the study area is flat or slightly undulated, very fertile, with numer- ous rivers and streams and an average elevation of 349 m. Mean annual temperature is 20.7°C, ranging from 14.5°C in July (winter) to 25.8°C in January (summer). The rainy season starts in November as an annual monsoon, which lasts through the summer and into early fall; mean annual rainfall is 862 mm with a maximum monthly mean of 191 mm in January and a minimum monthly mean of 4 mm in July. Similar habitats and topography continue to the South (to Tucumán Province) and the North (to Oran, in Salta Province). The original biome of the area is a subtropical forest called “the yungas forests,” with numerous tree species of high economic value (Anadenanthera colubri- na, Calycophyllum multiflorum, Phyllostylon rhamnoides, Astronium urundeuva, Maclura tinctoria, Cordia tri- chotoma, among others). This forest area is now consider- ably fragmented and modified by human agricultural activities. The main cultivated crop is sugar cane, which is grown from May to November. Other products include cit- rus fruits, avocados, pears, bananas, mangos, papayas, cherimoyas, and vegetables. Agriculture is the main source of employment, mostly involving manual labor. Housing for agricultural laborers is typically of very poor construc- tion, in many cases consisting of shacks of salvaged wood and sheet metal. This type of domestic and peridomestic habitat offers prime conditions for rodent infestations, pro- viding easy rodent access and poor sanitation, and is found even in the urban area of Yuto. Population Survey A cross-sectional study was performed on a sample of the general population of the area (population 7,900). The estimated sample size to document the overall prevalence in the total population was approximately 340 persons. Figure 1 shows the distribution of the general population and that of the survey participants by sex and age. Local physicians explained the objectives of the study to partici- pants, and an informed consent agreement was signed by each person or by parents or legal guardians of minors. Each participant had a blood sample drawn and completed a questionnaire that covered personal data, ethnicity, RESEARCH Figure 1. Distribution of general population and survey population by sex and age. household and workplace characteristics, occupation, domestic sightings of rodents, recreational activities, time of residence in the area, history of travel inside and outside the country, previous disease compatible with HPS, and contact with a confirmed HPS patient. Rodent Study Trapping Site Selection Sherman live traps were placed at likely sites of expo- sure of previously documented HPS cases. Nine sites were selected: four sites in Yuto District (Guaraní [13 lines, 347 traps], Jardín [4 lines, 60 traps], 17 Has [4 lines, 124 traps], and 8 Has [7 lines,168 traps]); one in El Bananal, a small rural village 7 km outside Yuto (11 lines, 214 traps); three on or adjacent to farms (fincas [26 lines, 1,100 traps]); and one in a brushwood area (seminatural habitat [8 lines, 500 traps]). One farm was located in Urundel, Salta Province, in the immediate vicinity of Yuto, and the owner, workers, and inhabitants belonged to the Yuto community. Of the 73 capture lines, 19 were inside the household, 25 were peridomestic, 6 were in weeds near grapefruit culture, 5 in a brushwood, 5 at the side of a river or stream, 3 in veg- etable gardens, 3 at roadsides, 2 in fruit orchards, 2 at the edge of a canal, and 3 adjacent to wire fences, railroads, or gullies. Outside lines consisted of 25 traps, each separated by 5 m. Lines located inside and outside the houses corre- sponded both to rural and urban areas. The number of traps inside the houses and in peridomestic urban lines depend- ed on the area available at each site (8–20 traps). Figure 2 shows the location of trapping sites in Yuto and its sur- roundings. Trapping and Processing Trapping was performed from May 30 to June 4, 2000. Small mammals were collected each morning and trans- ferred to a field laboratory for processing. After being anesthetized with Isofluorane (Abbott Laboratories Ltd., Emerging Infectious Diseases • Vol. 9, No. 9, September 2003 1071