the hantavirus cross - sectional survey was carried out april through may 2006 in the municipality of uberlndia , minas gerais , at an average altitude of 863 m ( 1855s,4816w ) ( figure ) . a randomized and stratified ( sex and age ) sample
was collected from the entire rural area and from the south sector of the municipality s periurban area .
the term periurban refers to a residential area on the outskirts of the city that is in close contact with the rural area .
the participants answered a questionnaire that included demographic information ( sex , age , place of birth , and address ) and questions relating to hps risk factors ( type of dwelling , exposure to rodents at home or work , labor activity , risk activities , history of severe pneumonia , and direct contact with hps patients ) .
blood samples were collected by venipuncture , centrifuged , and sent to the laboratory of hantaviruses and rickettsioses at the oswaldo cruz foundation , rio de janeiro , brazil , for analysis .
we screened serum samples by elisa for hantavirus - specific immunoglobulin g using a recombinant antigen of the nucleocapsid protein of araraquara virus , produced in escherichia coli and supplied by the virus research unit of the university of so paulo , brazil , according to the procedure previously described ( 2 ) .
all positive serum samples were retested ; only those that had 3 elisa - positive results at > 1:400 dilutions were considered positive .
the mann - whitney u and fisher exact / binomial tests for 2 proportions were applied for comparison among medians and proportions , respectively , using epi info 3.3.2 ( www.cdc.gov/epiinfo ) and biostat 5.0 ( www.biostat.org ) software .
the 400 study participants comprised 200 rural and 200 periurban residents ranging in age from 12 to 76 years ( mean = 41 years ) .
the 8 rural area antibody - positive samples were from male farmers ( table 1 ) .
presence of antibody was significantly associated with male sex , older age class , and potential risk activities ( table 1 ) . although all case - patients reported exposure to rodents or their excreta , this exposure was not statistically significant ( table 1 ) . in the periurban area , the presence of antibody was associated with age but not with sex , risk activity , or exposure to rodents ( table 1 ) .
the mean age of seropositive persons from periurban and rural areas was similar ( p = 1.0 ) .
the relationship between antibody and sex depended on urban vs. rural residence ( p = 0.02 ) .
three antibody - positive persons in the rural zone and 2 in the urban zone reported a history of pneumonia , albeit without complications . *
clearing land , farming , working in pastures or cellars , or cleaning sheds barns , or other outbuildings .
the largest number of cases occurred among periurban residents , but the highest cumulative incidence was among rural residents ( table 2 ) .
nevertheless , rural and periurban areas did not differ significantly in either prevalence or incidence .
rural versus periurban . determined by using 2-tailed fisher exact or binomial tests for 2 proportions . 
overall hantavirus antibody prevalence among periurban residents was 2.0% , with a higher prevalence among women ( 2.6% ) . in previous studies , the prevalence of hantavirus antibodies was higher in men ( 46 ) .
this finding is similar to a situation reported in colombia , where all positive samples came from men engaged in rural activities ( 6 ) .
these activities involve a high risk for infection by hantaviruses ( 7 ) . in this study
, hantavirus positivity was found only in persons > 39 years of age , and the difference in the mean age of the participants in relation to positivity was significant .
this fact might suggest a historic high - risk event to which the older age class , but not the younger age class , was exposed .
high hantavirus antibody prevalence has been found in studies of some human populations in latin america ( 5,8,9 ) .
the prevalence of araraquara virus  reactive antibodies among the volunteers in this study demonstrates that transmission is not rare , reinforcing the hypothesis of the existence of mild disease or asymptomatic infections ( 10 ) .
two hypotheses have been proposed : clinically mild disease or inapparent infections might result from differences in the nature of exposure ( e.g. , low inoculum or inefficient mechanism of transmission ) or genetic differences in immune response to infection , or they might indicate the circulation of > 1 hantavirus genotypes of greatly reduced virulence ( 10,11 ) .
 a cross - sectional serosurvey was conducted to assess the proportion of persons exposed to hantaviruses in a virus - endemic area of the state of minas gerais , brazil . 
 findings of this study suggested the presence of > 1 hantaviruses circulating in this region causing hantavirus pulmonary syndrome , mild disease , or asymptomatic infection . 
The Study
Conclusions