study area and population : the study was carried out in the urban and 
 peri - urban areas of gulu and soroti towns in northern and eastern uganda , respectively 
 ( fig . 1fig .
gulu town had a population of 119,430 people in 21,622 households , while soroti 
 town had 41,711 people living in 9,768 households according to the 2002 household survey 
 .
map of uganda showing the location of gulu and soroti districts . the cattle population in gulu and soroti districts , where gulu and soroti towns are 
 located ,
we assumed that only 2% of the urban households in gulu ( 432 ) and 
 soroti ( 195 ) kept cattle as was the case in the capital city kampala , since no accurate data 
 were available for these 2 towns .
the cattle 
 were kept in herds as a mixture of different breeds , indigenous breeds ( ankole or zebu ) , 
 exotic breed ( friesian ) or crosses of indigenous and exotic breeds .
study design : a cross - sectional epidemiological study was carried out to 
 investigate the sero- prevalence of brucella and factors associated with 
 brucella sero - positivity in cattle in urban and peri - urban areas of gulu 
 and soroti towns .
each town was divided into urban and peri - urban areas using the population dynamics rapid 
 rural mapping method according to makita et al . .
this characterizes urban areas as those with a dense human 
 population with back yard farming on small plots , while peri - urban areas are transition 
 areas from rural to urban , with a high rate of population increase , new human residential 
 units and larger plots for crop cultivation .
there were 4 cattle grazing systems in the 
 study area ; communal grazing , tethering , paddocking and zero - grazing with the 
 characteristics according to table 1table 1.cattle production systems in urban and peri - urban gulu and sorotigrazing systemcharacteristicscommunal grazingindigenous breeds kept on a communal grazing land , 
 often with water and pasture scarcity and low level of commercial in-puts.tetheringsemi-intensive system with indigenous and cross - bred 
 cattle restrained by ropes in intensively cropped areas , or urban centres and 
 normally with herd sizes of 15 cattle and limited level of commercial in 
 puts.paddockingintensive or semi - intensive system with exotic or 
 cross- bred cattle confined in fenced units , often with improved pastures and 
 fodder .
herd sizes vary with acreage.zero-grazingintensive system with exotic or cross - bred cattle kept 
 and fed on fodder and crop residues in stalls .
herd size is usually small ( 13 or 
 up to 10 cattle for large scale farmers).source : mwebaze , 2006 . .
a list of herds in the study 
 areas was generated with the help of extension workers and farmers .
the herds were assigned 
 numbers , and the selection of herds for inclusion in the study was done by simple random 
 sampling . based on assumption that only 2% of urban and peri - urban households kept cattle 
  and desirous of sampling at least 25% of 
 cattle keeping households in respective study areas as done by matope et 
 al .
, a total of 116 herds were selected 
 in gulu and 50 in soroti .
the total targeted number of cattle to be sampled per district was 
 385 basing on the expected brucella sero - positivity in cattle of 50% ( since 
 no studies had been done ) , 95% confidence interval and a desired precision of 5% as 
 described by thrusfield .
however , more animals 
 than these were sampled in order to increase on the study precision . in each randomly 
 selected herd with less than 10 adult cattle ( > 6 months old ) , all animals were sampled , 
 whereas in herds with more than 10 cattle , 10 cattle were randomly sampled plus an 
 additional 20% of the remaining cattle . source : mwebaze , 2006 .
ethical statement : this study entailed collection of animal samples and 
 interviewing of farmers .
ethical clearance was obtained from the ethical review committee of 
 the college of veterinary medicine , animal resources and biosecurity , makerere university . 

the farmers were informed about the study , and their verbal consent was sought prior to 
 commencement of data collection .
collection of data and blood samples : blood samples , individual cattle and 
 herd data were collected in the dry season from the study herds from may to late july 2011 
 for gulu and from january to early march 2012 for soroti . in each selected herd ,
an 
 interview was carried out using a structured open and closed ended questionnaire 
 administered by trained local research assistants conversant in english and respective local 
 languages .
the information elicited included farmer s awareness of brucellosis risk factors 
 in cattle , the grazing system used , cattle numbers , breeding method , species kept on the 
 farm and the intra - household gender involvement in the keeping of cattle .
these interviews 
 and the data are thus based on self - reporting from farmers .
blood was collected from the mid coccygeal or the jugular vein into sterile vacutainer 
 tubes without anticoagulant ( bd , plymouth , u.k . ) .
variables were collected for all the 
 samples taken including ; town , date , herd , urban or peri - urban , geographic location 
 ( latitude and longitude coordinates collected by a global positioning system ( gps ) 
 receiver ) , identity of animal sampled , breed , sex and brucellosis vaccination status .
blood 
 samples collected and properly identified were allowed to clot , and serum was then harvested 
 immediately in the field in 2 ml cryogenic vials ( sarstedt , germany ) .
the 
 sera were transported at 4c to the college of veterinary medicine , makerere university , 
 kampala , and stored at 20c in sterile cryogenic vials until tested .
detection of antibodies to brucella : antibodies to 
 brucella in serum were detected using brucella indirect 
 elisa kit ( svanovabrucella - ab i - elisa ) .
the positive reactors 
 were confirmed using brucella competitive elisa kit 
 ( svanovabrucella - ab c - elisa ) .
both kits were procured from 
 svanova biotech ab uppsala , sweden , and the analyses on the sera were performed following 
 the manufacturer s recommendations .
the svanovabrucella - ab 
 i - elisa has sensitivity ( se ) of ( 95.1% ) and specificity ( sp ) of ( 97.6% ) , and if this is 
 coupled with the higher sensitive ( 99.5% ) and specific ( 99.6% ) 
 svanovabrucella - ab c - elisa , false positives due to 
 vaccination six months after vaccination may be ruled out [ 20 , 21 ] . however , there is no national 
 vaccination program against brucellosis in uganda .
the i - elisa assay was b. 
 abortus and bovine specific and the c - elisa assay was a multispecies assay 
 capable of detecting both b. abortus and b. melitensis 
 antibodies , and both have higher sensitivity than standard tests like complement fixation 
 test ( cft , 91.8% se ) , but with comparable specificity to cft ( 99.9% ) .
each serum sample was run in duplicates on brucella - ab i - elisa kit , and 
 samples with a percent positivity ( pp ) 40 were considered positive .
the pp was calculated 
 as ( mean optical density ( od)sample / mean odpositive control )  100 
 where od is the optical density .
the brucella - ab i - elisa positive samples 
 were then run in duplicates on brucella - ab c - elisa kit , and samples with a 
 percent inhibition ( pi ) 30% were considered positive .
the pi was calculated as 100  [ ( mean 
 odsamples  100 ) / ( mean odconjugate control ) ] .
positive and 
 negative control sera were included in each test for test validity according to instructions 
 from the manufacturer . statistical analysis :
the data obtained was captured in the ms excel , 
 edited for accuracy and then exported to the statistical package for social scientists 
 ( spss ) version 17.0 program to establish associations between sero - prevalence of brucellosis 
 and the risk factors at 95% level of confidence .
summary statistics , univariable and multivariable analyses 
 were carried out to identify associations between selected risk factors and 
 brucella sero - positivity at individual animal and herd levels .
the 
 confidence intervals of point estimates of proportions were calculated using vassarstats 
 software ( www.vassarstats.net ) .
the animal level sero - prevalence was the proportion of 
 positive animals out of the total number of animals sampled and analyzed , while the herd 
 level sero - prevalence was the proportion of herds with at least one positive animal out of 
 the total number of herds sampled .
following the summary statistics that showed a considerable difference in sero- prevalence 
 between the two towns , the analysis for factors associated with brucella 
 sero - positivity was made separately for the two towns .
initially , univariable analyses were performed on all herd and animal level variables for 
 each of the 2 regions .
variables with a p value of < 0.25 on likelihood 
 ratio chi - square test were included in multivariable models , after checking for 
 collinearity .
variables were deemed collinear if they had a variance inflation factor ( vif ) 
 of 10 , and in such a case , only one of the collinear variables deemed biologically more 
 plausible was included in the multivariable model .
abortion history and retained placenta at 
 individual animal level were considered in a model involving only females above two years of 
 age .
two multivariable logistic regression models were built to investigate risk factors 
 associated with brucella sero - positivity on herd and animal level , 
 respectively .
the wald s backward selection and iterative maximum likelihood tests were used 
 until variables in the models showed a p value of 0.05 .
hosmer - lemeshow test and diagnostic plots were 
 used to ascertain the goodness of fit of the models .
adjustment for intra - herd clustering 
 for individual animal risk factors was done by fitting a generalized linear mixed model 
 ( glmm ) including the fixed effects for the regressors and the random effect of the herd .
spatial analyses of sero - positive and sero - negative herds were done using qgis ( quantum gis 
 1.7.3 wroclav ) .
spatial epidemiological analyses for herd level brucella 
 seropositivity clustering effects were analyzed using the bernoulli model in spatial scan 
 statistics , satscan version 9.1.1 .
significant clusters based on the distribution of 
 likelihood ratio and its corresponding p - value were identified after 
 running the analysis for 999 permutations ( type i error set at 0.001 ) by monte - carlo 
 simulation .
we used a standard purely spatial scan statistic at 10% that imposed a circular 
 scanning window .
descriptive statistics : a total of 500 sera were collected in 116 cattle 
 herds in gulu and 507 sera collected from 50 herds in soroti town .
the individual 
 animal - level and herd - level sero - prevalence were 7.5% ( 76/1007 , 95% ci : 6.159.4% ) and 27.1% 
 ( 45/166 , 95% ci : 20.934.3% ) , respectively .
individual animal level sero - prevalence tended 
 ( p=0.08 ) to be higher in soroti than in gulu , and the herd - level 
 sero - prevalence was significantly higher ( p<0.001 ) in soroti ( table 2table 2.number of included herds and animals and brucella 
 sero - prevalencedistrictgulufraction95% ci : sorotifraction95% ci : lowerupperlower upperurban herds28 - --9 - --herd sero - prevalence28.6%8/2814%48.9%44.4%4/915.3%77.3%serum samples81 - --108 - --animal sero - prevalence12.3%10/816.4%22%5.6%6/1082.3%12.2%peri - urban herds88 - --41 - --herd sero - prevalence15.9%14/889.3%25.6%46.3%19/4131%62.4%serum samples419 - --399 - --animal sero - prevalence4.8%20/4193%7.4%10%40/3997.3%13.5%total herds sampled116 - --50 - --total serum samples500 - --507 - --overall herd sero - prevalence19%22/11612.90%27.10%46%23/5033%59.60%overall animal sero - prevalence6%30/5004.20%8.40%9.10%46/5076.90%11.90% ) . in both gulu and soroti , males headed the majority of households keeping cattle ( 67% and 
 90% , respectively ) and owned the majority of the herds ( 57% and 92% , respectively ) .
in 
 soroti , 98% of the herds shared a grazing ground compared to 43% in gulu .
out of 300 female cattle of reproductive age ( above 2 
 years old ) in gulu , 5% had aborted , and 3% had retained placenta . none of the animals that 
 had aborted or had retained placenta were sero - positive for brucella in 
 gulu . out of 310 female cattle of reproductive age in soroti ,
sero - prevalence of brucellosis in cattle with a history of abortion and 
 retained placenta in soroti was 8% and 11% , respectively .
there was no significant 
 association between history of abortion and sero - positivity , or retained placenta and 
 sero - positivity .
the gender of household head , the ownership of the cattle , sharing grazing 
 ground , abortion history at herd and individual animal level , an individual animal s history 
 of retained placenta and keeping goats in addition to cattle , showed 
 p - values > 0.25 in both districts and are not presented in detail .
the characteristics of the 
 farms and plausible risk factors ( p<0.25 ) for sero - positivity in the 2 
 towns are shown in table 3table 3.descriptive statistics and univariable analyses of plausible risk factors for 
 seropositivity to brucella at herd level in gulu and sorotivariablecategorygulusorotin ( % ) % sero posp - valuen ( % ) % sero posp - valuefarm locationperi - urban88 ( 76)160.1741 ( 82)461.00urban28 ( 24)299 ( 18)44cattle attendanthusband27 ( 23)110.1212 ( 24)500.64wife46 ( 40)155 ( 10)20children22 ( 19)1813 ( 26)46hired worker21 ( 18)3820 ( 40)50herd size15 cattle75 ( 65)160.0014 ( 8)00.03610 cattle17 ( 15)020 ( 40)501120 cattle11 ( 10)2711 ( 22)27>20 cattle13 ( 11)5415 ( 30)67herd breedexotic breed53 ( 46)150.111 ( 2)00.523mixed breeds31 ( 27)3210 ( 20)50indigenous breed24 ( 21)839 ( 78)46cross breed8 ( 7)250 ( 0)0breeding systemartificial insemination57 ( 49)180.650 ( 0)00.21communal bull45 ( 39)1848 ( 96)44non communal bull14 ( 12)292 ( 4)100grazing systemzero - grazing54 ( 47)170.130 ( 0)00.18communal grazing19 ( 16)3238 ( 76)40tethering36 ( 31)1112 ( 24)67paddocking7 ( 6)430 ( 0)0watering systemindividual water70 ( 60)140.152 ( 4)501.000communal water46 ( 40)2648 ( 96)46management of aborted material and 
 afterbirthbury them51 ( 44)160.4817 ( 34)590.24do nothing65 ( 56)2233 ( 66)39introduction of new cattle in last 2 
 yearsno84 ( 72)160.1817 ( 34)230.04yes32 ( 28)2833 ( 66)58keeping sheepyes20 ( 17)170.0627 ( 54)410.57no96 ( 83)8323 ( 46)52keeping dogsyes63 ( 54)240.1638 ( 76)530.11no53 ( 46)1312 ( 24)25only factors associated with seropositivity at p<0.25 in at least 
 one of the towns are shown .. only factors associated with seropositivity at p<0.25 in at least 
 one of the towns are shown .
univariable analyses of herd level risk factors in gulu identified farm location , cattle 
 attendant , herd size , herd breed , grazing system , watering system , introduction of new 
 cattle and keeping sheep and dogs as plausible risk factors with p<0.25 . 
 in soroti town , the herd size , breeding system , grazing system , management of aborted 
 material and after birth , introduction of new cattle in the last two years and keeping dogs 
 were identified ( table 3 ) .
univariable analyses 
 of individual animal level risk factors in gulu identified animal breed , age and region of 
 origin as plausible risk factors with p<0.25 , while in soroti town , 
 animal age was the only plausible risk factor ( table 
 4table 4.descriptive statistics and univariable analyses at individual animal level in 
 gulu and sorotivariablecategorygulusorotin ( % ) % sero posp - valuen ( % ) % sero posp -valueanimal breedcross - bred22 ( 4.4)50.0120 ( 3.9)50.812friesian96 ( 19)91 ( 0.2)0zebu317 ( 63)4469 ( 93)9ankole65 ( 13)1417 ( 3)6age12 years91 ( 19)60.01100 ( 20)50.18>25 years288 ( 58)4161 ( 32)8>57 years77 ( 15)10135 ( 27)10>7 years44 ( 8.8)16111 ( 22)14region of originwestern uganda51 ( 10)160.0010 ( 0)e**central uganda42 ( 8.4)140 ( 0)e*eastern uganda0 ( 0)0507 ( 100)9northern uganda407 ( 81)40 ( 0)e*only factors associated with sero - positivity at p<0.25 in at 
 least one of the towns are shown . *
no statistic is computed , because region of origin 
 is constant , e * result undefined . ) . only factors associated with sero - positivity at p<0.25 in at 
 least one of the towns
no statistic is computed , because region of origin 
 is constant , e * result undefined .
risk factors for brucella abortus sero - positivity at individual and herd levels in 
 gulu : herd size , the breed and age of the animal and its region of origin ( place 
 of purchase ) were significantly ( p<0.05 ) associated with 
 brucella sero - positivity in gulu in the univariable analysis ( tables 3 and 
 4 ) . in the multivariable model adjusting for intra - herd clustering of individual 
 animal risk factors in gulu town , the age of the animal ( p=0.007 ) and its 
 region of origin ( p<0.0001 ) ( place of purchase ) were associated with 
 sero - positivity ( table 5table 5.glmm analyses adjusting for intra - herd clustering of animal level risk factors in 
 guluvariablecategoryp - valueor95% ci for orlowerupperage0.00712 years ( ref)-1.0 - ->25 years0.1440.40.111.38>57 years0.1862.50.649.87>7 years0.0963.50.8014.84region of origin of the cow<0.0001western uganda ( ref)-1.0 - -central uganda0.0670.140.021.15northern uganda0.0090.090.020.57 ) .
large herd size was significantly associated with sero - positivity 
 ( p=0.003 ) , as indicated in table 
 6table 6.multivariable analyses of herd risk factors for brucella 
 seropositivity in cattle in soroti and gulucategoryp - valueor95% ci for orloweruppervariable in sorotiintroduction of new cattle in last 2 
 yearsno ( ref)-1.0 - -yes0.0274.41.216.4variable in guluherd size0.0315 cattle ( ref)-1.0 - -610 cattle0.998 - --1120 cattle0.222.60.612>20 cattle0.0027.8229 where herds with > 20 cattle were 7.8 times more likely to test 
 sero - positive compared to those of 15 cattle .
ankole cattle kept in herds with more than 20 
 cattle were 3.3 times more likely to test sero - positive compared to other breeds or their 
 counterparts in smaller herds ( p=0.016 ; odds ratio ( or ) = 3.3 ; 95% c.i for 
 or : 1.28.9).the hosmer - lemeshow test showed that the models fitted the data at both the 
 herd and individual levels ( =0.234 , df=4 , p=0.994 ; 
 =2.510 , df=4 , p=0.643 ) .
risk factor for brucella abortus sero - positivity at individual and herd levels in 
 soroti : introduction of new cattle was significantly associated with 
 brucella sero - positivity both at univariable ( p=0.04 ) 
 and multivariable ( p=0.027 ) analyses ( tables 3 and 6 ) .
the hosmer - lemeshow 
 test showed that the model fitted the data at herd level ( =4.591 , df=7 , 
 p=0.71 ) .
no risk factors were significantly ( p<0.05 ) 
 associated with sero - positivity at individual animal level in soroti , and thus , the 
 intra - herd clustering effect was not computed .
spatial distribution of sero - positive herds and their characteristics : the 
 spatial distribution of sero - positive and sero - negative herds in the 2 study areas is shown 
 in figs . 2fig .
2.map of gulu district showing the location of cattle herds included in this study . 

red dots : 
 brucella sero - positive herds ; blue dots : 
 brucella sero - negative herds . and 3fig .
3.map of soroti district showing the location of cattle herds included in this study . 

red dots : 
 brucella sero - positive herds ; blue dots : 
 brucella sero - negative herds ; green circle : the significant 
 cluster .. in soroti , 2 patterns of brucella herd seropositivity 
 were observed , one in which disease was homogenously distributed ( 39 herds ) and the other in 
 which it was clustered ( 11 herds ) .
this significant ( p=0.033 ) cluster of 
 sero - positive herds was centerd at 33.613270 n , 1.642567 e in obila village , otatai parish , 
 asuret sub - county , soroti and had 11 herds of which 9 were observed to be sero - positive and 
 in a radius of 5 km .
the number of expected cases of sero - positive herds was 3 , 
 assuming that the cases were randomly distributed in space .
the log likelihood ratio for 
 this cluster was 8 , and the relative risk within this cluster was 3.5 at 95% level of 
 confidence . in gulu , there was no evidence for a geographically differential risk of 
 brucella sero - positivity in cattle at herd level .
map of gulu district showing the location of cattle herds included in this study . 

red dots : 
 brucella sero - positive herds ; blue dots : 
 brucella sero - negative herds .
map of soroti district showing the location of cattle herds included in this study . 

red dots : 
 brucella sero - positive herds ; blue dots : 
 brucella sero - negative herds ; green circle : the significant 
 cluster .
this was the first study to document the sero - positivity to brucella 
 antibodies and factors associated with sero - positivity in cattle in 2 towns of northern and 
 eastern uganda at different stages of urbanization .
we found significant differences in the 
 herd sero - prevalence between the towns and common as well as different risk factors for 
 sero - positivity in the 2 towns .
the overall herd and individual animal - level sero - prevalence in this study were lower 
 ( 7.5% ) than what was found in studies in rural areas of uganda ( 15.8% , 10.2% and 10% ) [ 2 , 19 , 23 ] , but higher than that found in the urban peri - urban 
 area of kampala ( 5% ) , the capital city of uganda .
this observation suggests that there may be variations in risk factors for 
 brucella transmission in cattle related to the geographical location of 
 the animal i.e. rural or urban .
this finding is consistent with previous reports on the 
 disease , where the sero - prevalence was highest in rural areas , followed by peri - urban areas 
 and least in urban areas .
soroti town in eastern uganda had higher herd brucella sero - prevalence 
 than gulu town in northern uganda . our study finding of higher herd - level 
 brucella sero - prevalence in soroti than gulu may be difficult to explain , 
 but the observed predominant communal grazing and watering systems that allow more mixing of 
 herds in the former as opposed to zero grazing and individual herd watering in the latter , 
 may be implicated .
these findings concur with previous studies that reported high 
 brucella sero - prevalence in herds that practiced free - grazing as compared 
 to restricted grazing [ 8 , 14 ] .
it could also be related with the introduction of more new cattle in 
 soroti ( 66% ) than gulu ( 28% ) , since herds that introduced new cattle were more likely 
 ( or=4.4 ) to test positive in soroti .
this is supported by the evidence in previous studies 
 where management practices , the scale of the herd and the production system influenced 
 sero - positivity and culling [ 8 , 12 , 20 , 30 ] .
in gulu town , the herd size was significantly associated with herd sero - positivity , and the 
 animal s age and its region of origin were significantly associated with individual animal 
 sero - positivity .
this 
 is most likely due to increased chances of animal to animal contact in larger herds than 
 smaller ones . the high individual animal 
 sero - prevalence observed in cattle from western uganda concurs with previous studies that 
 reported sero - prevalence of 21.5% and 10.2% , respectively [ 11 , 19 ] .
the reported high risk in older 
 cattle compared to young cattle agrees with the literature about the disease , which is due 
 to increase in the chances of getting exposed to brucella over time .
sero - prevalence being higher in the 12 years age 
 category than the 25 years age category could be due to presence of maternal antibodies in 
 animals of 12 years .
the observed high 
 sero - prevalence in the ankole cattle compared to other breeds suggests that there is breed 
 variation in susceptibility agreeing with findings of paixo et al .   and haileselassieet al . .
considering not doing a complete coverage of all herds in the study area for spatial 
 analyses , the interpretation of the results from this analysis needs to be interpreted 
 carefully .
however , the observed clustering of brucella in soroti herds 
 could be due to the herd structure and management practices within the herds in the 
 brucella sero - positive cluster that facilitated mixing of the herds . 

likely , the small herd size observed in the cluster facilitated their easy movement and 
 eventual congregation in communal grazing areas where they were tethered or grazed freely 
 increasing the animal density , thus facilitating transmission of brucella . 

this finding is consistent with that of hegazy et al .   in upper egypt .
the study finding of insignificant association between history of abortion and 
 sero - positivity , or retained placenta and sero - positivity points to possible occurrence of 
 other abortifacients and causes of retained placenta in cattle in the study areas .
probable 
 causes could be tick borne diseases which are known to be highly prevalent in the study 
 areas as established by ocaido et al . , or infectious causes of abortion like leptospirosis that has been reported in 
 uganda   or dietary deficiencies as most of these 
 cattle were not supplemented .
this calls for further research to determine the exact cause 
 of these abortions . in conclusion , the present study reports high herd - level prevalence of brucella 
 antibodies in cattle in two towns in northern and eastern uganda as well as a set 
 of risk factors for sero- positivity . in gulu town ,
older cattle , region of origin of the 
 cattle and large herd size were identified as risk factors for brucella 
 sero - positivity , whereas in soroti town , introduction of new cattle was identified .
this 
 shows that risk factors for brucella sero - positivity in urban and 
 peri - urban cattle in the two studied areas differed .
this in turn calls for a tailored 
 approach when designing control measures for prevention of transmission of bovine 
 brucellosis in different areas .
 brucellosis is a key zoonosis of major public health , animal welfare and 
 economic significance , and is endemic in livestock in uganda . 
 a cross - sectional 
 epidemiological study was carried out to estimate the sero - prevalence of brucellosis and 
 identify factors associated with sero - positivity in cattle in urban and peri - urban gulu 
 and soroti towns of northern and eastern uganda , respectively . 
 a total of 1007 sera and 
 data on biologically plausible risk factors from 166 herds and their spatial locations , 
 were collected from cattle reared in urban and peri - urban gulu and soroti towns of uganda . 
 
 the sera were analyzed using indirect elisa and sero - positive reactors confirmed by 
 competitive elisa . 
 multivariable models were used to investigate for risk factors . 
 the 
 overall animal - level and herd - level sero - prevalence was 7.5% ( 76/1007 , 95% confidence 
 interval ( ci ) : 6.159.4% ) and 27.1% ( 45/166 , 95% ci : 20.934.3% ) , respectively . 
 herd - level 
 sero - prevalence was significantly ( p<0.001 ) higher in soroti than 
 gulu . 
 in gulu town , sero - positivity increased with an increase in herd size 
 ( p=0.03 ) and age ( p=0.002 ) , and was higher in cattle 
 brought in from western uganda ( p<0.0001 ) . in soroti town , 
 
 introduction of new cattle into a herd was significantly ( p=0.027 ) 
 associated with herd sero - positivity . 
 there was a geographically differential risk 
 ( clustering ) of brucella sero- positivity in herds in soroti , while 
 sero - positivity was homogeneously distributed in gulu . 
 the data highlight brucellosis 
 occurrence and major risk factors for its transmission in cattle in urban and peri - urban 
 areas . 
MATERIALS AND METHODS
RESULTS
DISCUSSION