RESEARCH Figure 2. Localization of rodent trapping sites in Yuto and its sur- roundings. Queenborough, England), animals were bled from the retroorbital sinus by using heparinized capillary tubes, and then killed by cervical dislocation while still anesthetized. Samples of serum, blood clot, brain, heart, kidney, liver, and lung were placed in cryovials and stored in liquid nitrogen for their subsequent analysis at the Instituto Nacional de Enfermedades Virales Humanas (INEVH). Carcasses were tentatively identified in the field and pre- served in 10% formalin and sent to the Natural Sciences Museum “Miguel Lillo” in San Miguel de Tucumán for taxonomic confirmation. Small mammal trapping and pro- cessing were performed according to established safety guidelines (7). Serology Human blood samples were centrifuged at Yuto Hospital. Serum was separated and placed in cryovials and stored in liquid nitrogen until further testing at INEVH. Rodent samples were centrifuged in the field laboratory and stored as described. Hantavirus antibodies were detected by an ELISA. Briefly, 96-well polyvinyl microplates were coated with SNV recombinant and con- trol antigen overnight; then, serum samples and positive and negative controls were applied, followed by a peroxi- dase-conjugated antihuman IgG for human serum and a mix of peroxidase-conjugated anti–Rattus norvegicus and anti–Peromyscus maniculatus IgG for rodent serum. The substrate applied was 2,2′-azino-di (3-etilbentiazolin sul- fonate) (ABTS, Kierkegaard & Perry Laboratories, Inc., Gaithersburg, MD). Serum dilutions were considered pos- itive if the optical density was >0.2 after adjusting by sub- traction of the corresponding negative-antigen optical den- sity. Serum samples with titers >1:400 were considered positive. Results Serologic Survey in the General Population Hantavirus IgG was found in 22 (6.5%) of 341 serum samples tested. For males, hantavirus antibody prevalence was 10%; females had a prevalence of 3.7%. Among the 341 participants, 56 were <10 years of age, 239 were 11–50 years of age, and 45 were >51 years of age (1 was without age data). Mean age among antibody-positive per- sons was 41 (range 18–87); 77% of these were in the 11- to 50-year age group. Hantavirus antibody prevalence according to sex and age are shown in Table 1. Most (292/341, 85.6%) of the population in the survey were local born or native Argentinians. Twenty-five (7.3%) participants were foreigners, including 24 Bolivians and 1 Paraguayan. Twenty-two persons had abo- riginal ancestors (6.5%), with 17 belonging to the Guarani community. No information was available for two persons. Only one of the aboriginal participants had IgG antibodies to hantaviruses (1 [4.5%] of 22). Table 2 shows hantavirus antibody prevalence among the study population by eth- nicity or nationality. Dwellings were characterized according to their loca- tion as urban (>500 m from an open field), suburban (50–500 m from an open field), and rural (<50 m from an open field). Table 3 shows hantavirus antibody-prevalence Table 1. Serologic findings for hantavirus antibodies by age, sex Females Males Age (y) No. positive/tested (%) No. positive/tested (%) 0–9 0/29 (0) 0/23 (0) 10–19 0/45 (0) 2/28 (7.1) 20–29 1/28 (3.6) 3/35 (8.6) 30–39 0/30 (0) 4/28 (14.3) 40–49 4/30 (13.3) 3/18 (16.7) 50–59 0/21 (0) 1/9 (11.1) >60 2/8 (25) 2/10 (20) Without data 0/1 Total 7/191 (3.7) 15/150 (10) 1072 Emerging Infectious Diseases • Vol. 9, No. 9, September 2003