RESEARCH Table 4. Hantavirus antibody prevalence by clinical and epidemiologic characteristics Yes No Without data Positive/tested (%) Positive/tested (%) Chi square,a p value Positive/tested (%) Previous clinical HPSb symptoms 3/29 (10.3) 19/307 (6.2) 0.75, 0.38 0/5 (0) Contact with a confirmed HPS case-patient 6c/98 (6.1) 16/242 (6.6) 0.03, 0.86 0/1 (0) Recreational activities (fishing, hunting) 6/77 (7.8) 16/260 (6.2) 0.26, 0.60 0/4 (0) Sighting of rodents 17/270 (6.3) 5/71 (7.0) 0.05, 0.81 Trips outside the area 15/233 (6.4) 7/105 (6.7) 0.01, 0.93 0/3 (0) aChi-square test for comparison of two proportions in two independent samples, p>0.05 no significance. Epi Info version 2000 (Centers for Disease Control, Atlanta, GA). bHPS, hantavirus pulmonary syndrome. cAll positive contacts were relatives of a confirmed HPS patient. Discussion The differences observed in the South American han- tavirus infections relative to the classical SNV-related syn- drome in North America have been suggested to reflect approaches to surveillance and differences in the patho- genicity of the viruses, host-reservoirs, and ecologic fac- tors. The particular pattern of mild clinical illnesses and low case-fatality rate found in Yuto determined our selec- tion of the area for detailed studies. In this first investiga- tion, we attempted to determine the prevalence of past infection in the general population by testing for han- tavirus IgG antibodies, to identify risk factors, and to iden- tify the rodent species implicated in the transmission of hantaviruses The hantavirus antibody prevalence found in the human population survey is one of the highest reported in Argentina, with a mean of 6.5% (females 3.7%, males 10%). Previous studies in the other HPS-endemic areas (central and southwestern) of Argentina found antibody prevalence varying from 0.1% to 1.5% (4,8). Males in their 30s and 40s showed antibody prevalences of >14% and 16%, respectively. Most antibody carriers (82%) did not report clinical manifestations consistent with HPS. Thus, the low case-death rate clearly reflects milder clinical ill- nesses (reported case-fatality rates are 40% to 50% in both Americas) (9,10). In previous studies of asymptomatic contacts of HPS case-patients from this area, we found a high prevalence of IgG (4 [9.5%] of 42). This finding could be the result of infection from a common source or interhuman transmis- sion (6), as described in the 1996 outbreak in El Bolson- Bariloche, southern Argentina (11–13). In this survey, we did not find differences in the hantavirus antibody preva- lence in persons with and without known HPS case contact (6.1% and 6.6%, respectively). No antibodies were found among the healthcare workers studied, and the distribution of clinical cases and antibody carriers by sex showed a pre- dominance of males (in patients from 1997 to 2000, the percentage of males was 76.7%, 23/30). These findings, collectively, do not favor the hypothesis that interhuman spread is playing a large role in the transmission of han- taviruses in this area. These findings also reinforce the view that environmental, occupational, and residential fac- tors create an increased risk for rodent exposure in occupa- tional, domestic, and peridomestic settings. This conclu- sion is supported by the noticeable observation of rodents and their signs in households and workplaces reported by the study population and patients. The risk factor that showed a significant difference between antibody-positive and -negative persons was a rural occupation, especially one associated with agricultural activities. This finding was also reflected in the high male antibody prevalence Table 5. Relative abundance and hantavirus antibody prevalence of rodent species in Yuto (Jujuy Province) Order Family Subfamily Genus/species Captures (%) Rodentia Muridae Sigmodontinae Akodon simulator 140 (39.0) A. caenosus 3 (0.8) Akodon sp 2 (0.6) Calomys callosus 137 (38.0) Holochilus chacarius 11 (3.1) Oligoryzomys chacoensis 4 (1.1) O. longicaudatus 6 (1.7) Oligoryzomys sp 2 (0.6) Oxymycterus paramensis 3 (0.8) Murinae Mus musculus 10 (2.8) Rattus rattus 6 (1.7) Didelphimorphia Didelphidae Marmosinae Thylamys venustus 2 (0.6) T. elegans 1 (0.3) No identification 34 (9.4) Total 361 (100) 1074 Emerging Infectious Diseases • Vol. 9, No. 9, September 2003 No. positive/tested (%) 4/140 (2.8) 0/3 0/2 7/137 (5.1) 0/11 0/4 0/6 0/2 0/3 0/10 0/6 0/2 0/1 0/34 11/361(3.0)