with the increase in international travels and multiracial communities in the united states , non - rubella immune ( nri ) pregnant women as well as nonimmune individuals are at risk of rubella infection .
a study in 1988 suggested that between 7.5 and 17.4% of pregnant women in the united states lack immunity to rubella .
similarly , a prevalence rate of 15.1% among pregnant women was reported in 1999 by investigators in michigan .
in addition , a rate of 9.1% was found among women who attended prenatal care at lejeune nc in 2004 . in view of the recent report of two adult cases of rubella infection in the united states , the importance of identifying populations at risk for rubella infection can not be over emphasized .  
this may result in miscarriage , fetal death , or severe anomalies in the infant with crs .
infection during the first trimester of pregnancy is associated with worst outcomes and development of multiple organ anomalies associated with crs .
some of the effects of crs may not be apparent at birth   and may manifest as a chronic disease capable of producing ongoing organ damage throughout the life of an infected child .   
although the prevalence of crs and adult rubella infection declined remarkably following the introduction of rubella vaccine in 1969 in the united states [ 8 , 9 ] , the disease is still endemic in many developing countries . in many developing countries such as sub - saharan africa
, there is no existing national vaccination program against rubella , and surveillance data is limited [ 10 , 11 ] .
these developing countries are responsible for most of the estimated 238,000 global cases of children born annually with crs .    in the united states ,
the last major epidemic of the disease resulted in about 12.5 million cases of infection , 20  000 cases of crs and 11,000 fetal deaths .
sporadic cases of the disease still occur in the united states [ 14 , 15 ] because of lack of universal immunization , primary and secondary vaccine failure and reinfections [ 16 , 17 ] .
some sporadic cases in the united states have led to the association of race with rubella infection .
for instance , rangel and colleagues reported outbreak of rubella infection in a hispanic community in north carolina .
in addition , another outbreak was reported in meat processing plants that employed many hispanics and other foreign nationals in kansas and nebraska .
similarly , plotinsky and colleagues reported a case of crs in an infant born to a liberian refugee living in new hampshire . furthermore , during 1997 to 1999 , 81% of reported crs cases were hispanics and 92% of the infants were born to foreign mothers . apart from the numerous medical consequences of the disease [ 2124 ] , the economic cost of the disease is also enormous .
identification and protection of nri women of child bearing age against rubella will prevent crs and its associated morbidity , mortality , and economic health burden .  
the objectives of this study were to evaluate the prevalence and distribution of nri among pregnant women who attended multiracial high - risk prenatal clinic in 2007 .
findings from the study may provide the rationale for targeted public health intervention that may prevent reemergence of rubella .
this is a retrospective , chart review study involving pregnant women who attended high - risk prenatal clinic in northwestern iowa in 2007 .
this study was part of a routine evaluation of prenatal care in the clinic and approved by sioux city institutional review board , iowa , united states .
the clinic serves a diverse population of low - income and multiracial groups including a large hispanic population , non - hispanic whites , native americans , african americans , asians , and african immigrants living in the tri - state area of nebraska , iowa , and south dakota . during their initial prenatal visit , all patients gave blood samples for routine prenatal laboratory screening .
rubella screening was conducted by evaluating serum rubella igg antibody titer using enzyme linked immunosorbent assay ( elisa ) ( wampole laboratories , princeton , nj ) as described previously .
individuals with equivocal results and those with no rubella igg antibody were regarded as nonimmune .
single researcher extracted the data in microsoft excel ( microsoft corp . , redmond , wa ) for analysis .
prevalence rate in the study population was calculated by dividing the number of nri women with the total number of women screened during the study period .  
these include less than 20 years of age , or adolescent , 2029 years of age and 30 or more years of age .
nri prevalence rates in these age groups were calculated by dividing the number of nri in the age group by the total number of women screened in that age group .
furthermore , we evaluated the prevalence rates in four major study populations , namely , hispanics , whites , native americans , and african americans .
data was analyzed using sigma stat software ( jandel scientific , san rafael , ca ) .
statistical significance was established using chi square or fisher 's exact test . to control for possible differences in age distribution across race / ethnic groups ,
race / ethnic group was the primary explanatory variable , and whites were selected as the reference category for comparison purposes .
age was added to the unadjusted logistic model to determine the relationship between race / ethnicity and the presence or absence of rubella immunity while holding constant the influence of age .
non - hispanic population comprised of whites or caucasians ( 180 ) , african americans ( 34 ) , native americans ( 52 ) , asians ( 21 ) , and others ( 7 ) .
the asians , biracial ( 3 ) , and africans from somalia ( 4 ) were in the group classified as 
women aged 2029 years of age constituted the highest number of subjects and accounted for 57.9% of the study population .
adolescents and women 30 or more years of age accounted for 18.4% and 23.7% of the study population , respectively .  
the prevalence rate among native americans was highest at 17.3% , compared to whites 7.3% , blacks 5.9% , and hispanics 4.6% ( see figure 1 ) . in the study population , prevalence rate among adolescents was 10.2% compared to 6.2% and 5.9% among women aged 2029 and 30 or more years of age , respectively ( see figure 2 ) .
analysis of the trend in three major racial groups demonstrated a high rate among native american teenagers at 18.2% compared to whites and hispanics at 10.8% and 8.5% , respectively . in women aged 2029 years of age
, the rate among native americans was 11.5% compared to 7.4% and 3.2% of whites and hispanics , respectively . among older women ( 30 years or more ) ,
the prevalence rate among native americans was 26.7% compared to 0% and 4.9% of whites and hispanics , respectively .
the overall trend in nri in the three main racial groups demonstrated persistence of nri at a higher rate among native americans compared to whites and hispanics ( see figure 3 ) .  
crude and adjusted multivariate analysis demonstrated that native americans were more than two and a half times more likely not to have rubella immunity than whites ( or 2.7 ; 95% ci : 1.1 , 6.6 ) .
once we control for suspected differences in age distribution , the association remained ( or 2.7 ; 95% ci : 1.1 , 6.7 ) .
this study evaluated nri among women attending high - risk prenatal care in iowa , united states .
the prevalence rate of nri demonstrated in this study appeared lower compared to previous studies in 1988 ( 7.5%17.4% ) , 1999 ( 15.4% ) , and 2004 ( 9.1% ) .
one of the important findings of this study is the presence of comparatively higher nri among adolescents in the study population ( see figure 2 ) .
this finding supports rubella booster vaccination for nonpregnant women such as high school female teenagers .
secondly , booster vaccination may also prevent undiagnosed cases of rubella that resulted in congenital anomalies   and first trimester loss of pregnancy . since there is no effective treatment of infection during pregnancy that will prevent crs , protecting women before pregnancy is therefore an attractive public health intervention against crs .   
another important implication of this study is the finding of significant prevalence of nri across all age groups among the native american women .
compared to whites , native americans are more likely to be non - immune to rubella .
this finding calls for further studies and evaluation of mmr vaccination programs existing in native american communities .
replication of the findings in this study may warrant public health interventions aimed at protecting these communities from rubella epidemic . despite the important findings of this study
, it should be seen as a pilot study because of the imbalance in the study population .
however , the study may provide the basis for evaluation of longevity of immunity derived from rubella vaccine currently administered to children in the united states as part of mmr vaccine .
similarly , this paper may provide the rationale for further studies in native american communities targeted at elucidating factors that foster decreased immunity to rubella .
   since the introduction of the rubella vaccine in 1969 , prevalence of congenital rubella syndrome ( crs ) has greatly declined in the united states . 
 however , reports of sporadic adult cases of the disease and frequent identification of non - rubella immune ( nri ) women in prenatal units may result in outbreak of crs in susceptible communities . 
 identifying populations with high rates of nri will assist in evidence - based public health intervention that may prevent epidemic of crs in the united states . method . 
 this is a retrospective , cross - sectional study involving chart audit of rubella screening results of 642 women who attended a high - risk prenatal care at a northwestern iowa clinic between january 1 and december 31 , 2007 . results . 
 nri was found in 6.9% of the study population . 
 the highest prevalence rate of 10.2% was found among adolescents . 
 nri was highest among native american women at 17.3% , compared to whites 7.3% , african americans 5.9% , and hispanics 4.6% . 
 multivariate analysis demonstrated that native americans were 2.5 times more likely to be nri compared to whites ( or 2.7 ; 95% ci : 1.1 , 6.6 ) . conclusion . 
 this study demonstrated higher rate of non - rubella immunity among adolescent pregnant women and supports rubella booster immunization for all non - pregnant teenage women . 
 the observed high rate of nri among native americans may require further studies and evaluation of rubella vaccination programs in tribal communities . 
1. Introduction
2. Method
3. Results
4. Discussion