q fever is a zoonotic disease that is caused by coxiella burnetii , a microorganism that frequently infects domestic ungulates , as well as wild mammals in many genera ( 1 ) . in animals ,
the disease is transmitted to humans incidentally by inhalation of aerosols from infected cattle and sheep ( 1 , 2 ) . in humans , c. burnetii infection may be asymptomatic , acute , or chronic .
chronic q fever is rare , with endocarditis presenting as the most common complication ( 1 , 3 ) .
q fever has been reported in almost every country , except new zealand ( 4 ) . in canada ,
burnetii antibodies ( 5 ) . in japan , 60 to 84% of cattle with reproductive disorders are seropositive ( 6 ) .
a study conducted in southern france showed that 5 to 8% of endocarditis cases in humans were due to c. burnetii , and the prevalence of acute q fever was 50 cases per 100,000 inhabitants ( 7 ) .
researchers have suggested that the incidence of q fever is chronically underestimated because clinical manifestations of the disease are often nonspecific or even absent .
therefore , concerns with the disease focus on the importance of detection ( 1 , 3 , 8) . in korea
, there is a little information concerning the epidemiology of c. burnetii infection in either animals or humans .
a few cases of acute q fever in humans have been reported ( 9 , 10 ) .
we examined the prevalence of antibodies to c. burnetii in dairy cattle nationwide and in people for health screening in a rural area of korea , and used the data to evaluate the impact of q fever in both animals and humans in korea .
upon agreement with dairy owners , serum samples from 414 dairy cattle were collected on 31 farms from march to june , 2001 .
serum was collected from people who visited kangwon national university hospital for health examinations between april and december 2002 .
the subjects were interviewed to confirm the absence of symptoms of respiratory tract infection during the preceding two weeks .
informed consent was obtained from all people for health screening and the animals are treated by the ethical guidelines of kangwon national univesity .
coxiella burnetii phase ii antigen ( nine mile whole - cell antigen ) was prepared as previously described at the national institute of infectious diseases ( niid ) in tokyo , japan ( 12 ) , and dotted onto teflon - printed glass slides .
each serum sample was diluted 1:16 with phosphate - buffered saline ( pbs ) , overlaid on the antigen dots , and incubated for 45 min at 37 in a moist chamber .
the slides were subsequently washed twice for 5 min in pbs plus 0.05% tween-20 and then incubated with a 1:1,400 dilution of fluorescein isothiocyanate ( fitc)-conjugated rabbit anti - bovine igg ( sigma - aldrich , st .
louis , mo , u.s.a . ) or fitc - conjugated rabbit anti - human igg ( dakocytomation , glostrup , denmark ) for 45 min at 37 in a moist chamber .
the slides were again washed twice using the same method and examined using fluorescence microscopy ( axioskop 2 , zeiss , germany ) at 200 magnification .
all sera that produced positive or equivocal reactions at 1:32 were further analyzed using 2-fold serial dilutions up to 1:4,096 .
approximately 10% of the sera were divided and tested concurrently at kangwon national university and at the niid for quality control of test reproducibility ; there was greater than 95% concordance between the results from the two laboratories .
upon agreement with dairy owners , serum samples from 414 dairy cattle were collected on 31 farms from march to june , 2001 .
serum was collected from people who visited kangwon national university hospital for health examinations between april and december 2002 .
the subjects were interviewed to confirm the absence of symptoms of respiratory tract infection during the preceding two weeks .
informed consent was obtained from all people for health screening and the animals are treated by the ethical guidelines of kangwon national univesity .
coxiella burnetii phase ii antigen ( nine mile whole - cell antigen ) was prepared as previously described at the national institute of infectious diseases ( niid ) in tokyo , japan ( 12 ) , and dotted onto teflon - printed glass slides .
each serum sample was diluted 1:16 with phosphate - buffered saline ( pbs ) , overlaid on the antigen dots , and incubated for 45 min at 37 in a moist chamber .
the slides were subsequently washed twice for 5 min in pbs plus 0.05% tween-20 and then incubated with a 1:1,400 dilution of fluorescein isothiocyanate ( fitc)-conjugated rabbit anti - bovine igg ( sigma - aldrich , st .
louis , mo , u.s.a . ) or fitc - conjugated rabbit anti - human igg ( dakocytomation , glostrup , denmark ) for 45 min at 37 in a moist chamber .
the slides were again washed twice using the same method and examined using fluorescence microscopy ( axioskop 2 , zeiss , germany ) at 200 magnification .
all sera that produced positive or equivocal reactions at 1:32 were further analyzed using 2-fold serial dilutions up to 1:4,096 .
approximately 10% of the sera were divided and tested concurrently at kangwon national university and at the niid for quality control of test reproducibility ; there was greater than 95% concordance between the results from the two laboratories .
each province had a relatively high prevalence , ranging from 8.9 to 59.3% ; the overall national prevalence was 25.6% .
of the positive sera ( n=106 ) , 80 ( 75.5% ) had high antibody titers ( 1:256 ) .
the mean age of the subjects was 43.7 yr ( standard deviation 15.9 , range 19 - 82 ) , and the male - to - female ratio was 1:0.86 ( n=110:95 ) .
of these , one had a serum sample with a high antibody titer ( 1:512 ) , and two had samples with low antibody titers ( 1:64 ) ( table 2 ) .
this study examined the seroprevalence of c. burnetii infection in cattle and people for health screening in korea .
the sera of cattle showed a high prevalence ( 25.6% ) of anti - c .
burnetii antibodies , with 75.5% of the positive sera having high titers ( 1:256 ) .
by contrast , the sera of healthy people showed a relatively low prevalence ( 1.5% ) of anti - c .
the sera of dairy cattle were collected regardless of the disease status of each animal , which is a limitation of this study . since we could not find an association between a history of reproductive failure and seropositivity of the cows because of the absence of the data on the disease status , no prediction concerning seropositive status and reproductive problems can be made .
however , c. burnetii infection is prevalent in all areas of korea ; every region had a seroprevalence above 8% , and the national prevalence was 25.6% .
moreover , the high prevalence of high - titer sera provides evidence that the disease might be very active in this country . in neighboring japan , the seroprevalence of c. burnetii in healthy cattle ranges from 2 to 46% ; in cattle with reproductive disorders , the range was 60 to 84% ( 6 ) .
reported that bovine placentitis was highly associated with the presence of c. burnetti ( 13 ) .
in addition , 9% of abortions in goats are reported to be caused by this microorganism ( 14 ) .
this is the first report to provide data that suggest that c. burnetii infection might be one of the important causes of reproductive problems in cattle in korea .
further studies based on the isolation of c. burnetii are needed to elucidate the etiologic role of this microorganism in the reproductive problems of cattle in this country .
furthermore , the high seroprevalence of c. burnetii among cattle suggests the possibility of contamination of the environment around farms .
since c. burnetii is widely distributed in wild animals and ticks and causes q fever to humans ( 1 , 3 ) , it is necessary to evaluate the environmental hazards associated with c. burnetii infection that may threaten public health in the near future .
in addition , the survey on the high - risk group such as farmers and butchers is strongly needed .
the finding that people in a rural area demonstrated a relatively low seroprevalence of c. burnetii , as well as lower titers , suggests that infection with this microorganism seems to be relatively low in the rural area of korea . in a previously published report
( 11 ) , less than 1% of both healthy people and patients with fever of unknown origin tested positive for anti - c .
another report showed none of the sera from 70 healthy people was reactive for c. burnetii antigen ( 15 ) .
recent data showed that 11 out of 448 healthy people were reactive ( 16 ) .
on the other hand , our group previously reported that only one of 88 patients with community - acquired pneumonia was diagnosed with q fever with an ifa assay using both phase i and ii antigens ( 18 ) . despite the low seroprevalence of c. burnetii in humans
, we can not exclude the risk of q fever to individuals with high - risk occupations , such as farmers , veterinarians , and meat - processing workers , considering the high rate of infection observed in cattle in this study .
previous korean report showed two of 46 stock breeders had an antibody titer of 1:20 ( 15 ) , and 5 sera from 202 abattoir workers reacted with phase ii antigen ( 16 ) . in conclusion , c. burnetii appears to be a highly prevalent pathogen in cattle in korea and , accordingly , the studies on the high - risk groups are needed to evaluate the seroprevalence for this organism in korea .
 we report results on the seroprevalence of antibodies to coxiella burnetii in cattle and healthy people in korea . upon agreement with dairy owners , serum samples from 414 dairy cattle 
 were collected between march and june 2001 and samples from 205 people for health screening were collected between april and december 2002 . 
 the sera were analyzed for the presence of anti - c . 
 burnetii phase ii antibodies using an indirect microimmunofluorescence test ; strong fluorescence at a 1:32 dilution was regarded as positive . 
 the overall seroprevalence of c. burnetii in cattle in korea was 25.6% , with regional variation from 8.9 to 59.3% . 
 of the positive serum samples , 75.5% had antibody titers 1:256 . 
 by contrast , only 1.5% of people in a rural area were seropositive , and most of the positive samples had low antibody titers . in conclusion , this study showed that relatively high seropositivity of c. burnetii in dairy cattle , accordingly , the studies on the high - risk groups are needed to evaluate the seroprevalence for this organism in korea . 
INTRODUCTION
MATERIALS AND METHODS
Subjects
Indirect microimmunofluorescence antibody (IFA) assay
RESULTS
DISCUSSION