during 20012007 , a total of 4 communities ( 3 in los santos province and 1 in veraguas province ) within hantavirus - endemic agroecosystems in western panama were sampled 24 times at 1- to 3-year intervals ( table 1 ) . informed written consent consent and assent forms were reviewed and approved by institutional ethics review boards at the university of new mexico , the gorgas memorial institute in panama city , and the protocol review committee of the international centers for infectious diseases research program of the national institute of allergy and infectious diseases . eligible participants were all adults and children > 2 years of age who permanently resided in each community according to the 2000 national census . the reasons for noninclusion in the first and subsequent surveys were absence during the week of the survey and refusal to participate . * # increase for combining los santos localities and year , p = 0.0014 .  * * increase significant ( p = 0.001 ) . a questionnaire administered to the head of household asked for a history of respiratory - related illnesses and hospitalizations within the past 3 years . surveillance for hps was conducted in the same communities as the serosurvey and nationally through reports to the ministry of health , and cases of hps were confirmed by questionnaire . the diagnosis of hps required finding immunoglobulin ( ig ) m in acute - phase serum , detection of choclo virus rna in serum by reverse transcription pcr , typical respiratory signs and symptoms , and chest radiographic findings compatible with pulmonary edema . heparinized whole blood collected by arm venipuncture was separated by centrifugation ; plasma was stored at 20c until analysis . in binding assays , antibody to all known hantaviruses indigenous to the americas cross - react with the n protein of sin nombre virus ( 10 ) . a strip immunoblot assay for igg containing recombinant n protein of the 3h226 genotype of sin nombre virus was used as described ( 10 ) ; the criterion for positivity was a dark band for sin nombre n protein at a serum dilution of 1:200 . an enzyme immunoassay used recombinant nucleocapsid protein from sin nombre virus ( 11 ) ; the cutoff value was established at 3 sd above reactivity to a panel of known positive serum . all samples were tested by both assays ; the concordance of the enzyme immunoassay and strip immunoblot assay in this study was 97% , and the criterion for seropositivity was a positive reaction in both assays . loss of antibody in persons with previously positive serum was determined by 2 independent tests with both assays . all hps patients tested have had positive reverse transcription pcr results for choclo genomic rna in acute - phase blood samples ( 9 ) , and antibody has been detected by both assays . data were transferred from field collection forms to a database ( epi info version 6.04d , centers for disease control and prevention , atlanta , ga , usa ) for statistical analyses using epi info software . changes in seroprevalence within each community were tested by fisher exact test for each interval and by longitudinal analysis for all intervals and communities by a generalized estimating equation ( 12 ) . increases in seroprevalence according to community and year of survey were tested by using analysis of covariance . the 11 surveys repeatedly sampled 60%85% of the total population of each community , for a total of 1,838 samples from 1,129 persons . overall antibody prevalence was 32.9% , varying from 16.5% to 60.4% in individual surveys ( table 1 ) . in each of the 3 los santos communities ( agua buena , isla caas , san jose ) , seroprevalence increased annually by 5% ( table 1 ) ; the overall seroprevalence increases for the combined los santos communities were significant ( fisher exact test , p = 0.0014 ) . the changes in seroprevalence were community specific ( analysis of covariance f = 5.24 , p = 0.0043 ) , but increases in seroprevalence in the 4 communities combined was not ( general estimating equation ) . among the study population , seroconversion was documented for 70 persons , and hps was diagnosed for 5 other persons in the same communities during the intervals studied ( table 2 ) . in the cohort of 476 persons in all 3 los santos communities sampled in 2 back - to - back surveys ( table 2 ) , the 70 seroconversions occurred in persons in all age cohorts and equally among persons of both sexes ( data not shown ) . no person who seroconverted gave a history of hps - like illness or hospitalization for an acute respiratory illness . a separate study of outpatients with febrile illnesses was conducted in 4 clinics in the hantavirus - endemic area . this study found 48 adults and children with the typical febrile prodrome , unremarkable chest radiographs , and either serum igm specific for hantavirus nucleoprotein or choclo virus genomic rna in the acute - phase blood sample ( b. armien and j.m . these findings of symptomatic hantavirus infections confirm previous observations derived from neutralization - inhibition antibody assays ( 9 ) . no . seroconverted among subset who were seronegative at the beginning of the interval . no . seroreverted among subset who were seropositive at the beginning of the interval . the incidence of 70 seroconversions in 857 person - years of observation ( table 2 ) was equivalent to 8 infections per 100 person - years . the mean ages of persons who seroconverted ( 43 years ) and those with hps ( 43 years ) were the same . undercounting of hps cases was not likely because hps is a highly publicized illness throughout panama , and diagnostic serologic testing is readily available through the ministry of health . a total of 16 seroreversions , compared with 70 seroconversions , occurred among persons in most age cohorts , mean age 48 years . for hps caused by sin nombre and andes viruses , serum antibody typically persists for years ( 13 ) . antibody prevalence surveys are useful for identifying populations and locations at risk , monitoring changes in incidence , and focusing limited public health resources . determining whether the observed increases in seroprevalence will be sustained requires additional surveys , but this information will be useful as the new agroeconomy increasingly emphasizes the monoculture of products ( rice and sugar cane ) favorable to rodents ( 14 ) . nonetheless , the documentation of large numbers of mild or asymptomatic hantavirus infections not progressing to hps has identified a larger effect of this zoonotic disease .
during 20012007 , to determine incidence of all hantavirus infections , including those without pulmonary syndrome , in western panama , we conducted 11 communitywide surveys . among 1,129 persons , 
 antibody prevalence was 16.5%60.4% . 
 repeat surveys of 476 found that patients who seroconverted outnumbered patients with hantavirus pulmonary syndrome by 14 to 1 .