2 Infectious Diseases in Obstetrics and Gynecology Table 1: Measles and rubella immunities status. DISCUSSION Rubella Immune Not immune Measles Immune Not immune Indeterminate 780 10 62 7 41 0 rates of measles and rubella immunity. The Kappa statis- tic was utilized to assess concordance of immunity status. The paired data for each serum sample was evaluated us- ing McNemar’s test to evaluate whether or not there was a paired association between immunity statuses. The Wilcoxon rank-sum test was used for nonparametric comparison of the age means between immune and nonimmune individ- uals. RESULTS Nine hundred serum samples were obtained and tested for both measles and rubella immunities. The age of the women was known for 785 samples, with the average age 28 (range 14 to 44) years. Demographic data beyond age was unknown. However, the population of Iowa is primarily non-Hispanic white. As noted in Table 1, of the 900 samples tested, 790 were immune, 69 were nonimmune, and 41 were indeterminate to measles. Similar testing found that 883 samples were im- mune, and 17 were nonimmune to rubella (none of the rubella tests were indeterminate). All of the measles indeter- minate samples were found to be rubella immune. Immunity to measles and rubella was found to be 88% and 98%, respec- tively. Measles immunity status was noted for each rubella immune and rubella nonimmune sample groups to deter- mine the association of immunity status. The probability of measles immunity given that a sample was found to be rubella immune was 88%. There was no concordance be- tween immunity statuses, Kappa 0.1353 (95% CI 0.0314, 0.2392). Additionally, McNemar’s test rejected a paired asso- ciation between measles and rubella immunities, P < .0001. Even if all the serum samples found to be indeterminate for measles immunity were found to be measles immune, nei- ther concordance nor paired association would have been conﬁrmed (Kappa 0.1366, McNemar’s P < .0001). The mean age of those women in each rubella group (immune and non- immune) was the same (28 years). Thus, there was no appar- ent eﬀect of immunity status by age identiﬁed. The measles and rubella immunities prevalence identi- ﬁed in the population studied was diﬀerent than reported in the literature (noted previously). Therefore, a posthoc analysis was performed to determine power for the iden- tiﬁed measles and rubella immunities prevalence in our population using McNemar’s exact conditional test, with a computed power of > 0.999, and 0.0458 level of signiﬁ- cance. In 2005, the CDC independent panel concluded unani- mously that rubella was no longer endemic in the United States [3]. Unfortunately, there is still a signiﬁcant minority of reproductive age women who are rubella susceptible. The goal of prenatal testing is to identify women for vaccina- tion in the postpartum period as the measles-mumps-rubella (MMR) vaccine is contraindicated in pregnancy. The rubella vaccine was licensed in 1969. Since 1969, rubella-associated morbidity and mortality and the inci- dence of congenital rubella syndrome have greatly declined [2]. The rubella vaccine has been administered as part of the MMR vaccination since 1978. In 1990, a two-dose schedule was adopted (age 15 months and again at age 4–6 years). Following vaccination, measurable antibodies are present in 95% of individuals. Lasting immunity is present in 82% to 90% of those who initially seroconverted using the two-dose regime [4]. The measles vaccine was licensed in 1963. Since 1963, there has been a 99% reduction in the incidence of measles in the United States [2]. Unlike rubella, antepartum measles in- fection has no consistent pattern of fetal anomalies. However, there is a known increase in spontaneous abortions, prema- ture births, and maternal morbidity, including pneumonia and encephalitis. Passive immunization within six days of ex- posure is recommended in pregnant women [2]. We found that rubella immunity did not infer measles immunity in our study population. While correlation has been reported by others [5, 6] and was also noted in this study, correlation does not imply the more rigorous statis- tical associations of agreement or concordance. The large number of serum samples positive for both rubella and measles resulted in the correlation we identiﬁed, as would be expected in an immunized population. Strengths of our study include the large sample size, and prospective data analysis. A limitation of our study was that the serum samples were obtained from Midwest (primar- ily Caucasian) pregnant women, which limit generalizabil- ity. However, our ﬁndings agree with large military stud- ies where participants included both men and women from across the United States with varying ethnic background and race [4, 7, 8]. Measles immunity was found to be 88% and rubella im- munity 98%. The immunity rates for measles and rubella may diﬀer within the population we studied compared to those previously reported. Alternatively, the assay for measles antibody could be less sensitive than the assay for rubella an- tibody. This would be consistent with the high number of measles indeterminate results noted and could be related to the greater number of nonimmune measles results. Further Investigation may be undertaken to address this possibility. In conclusion, rubella immunity did not infer measles immunity in our population. In measles outbreaks as that in 2004, we would be unable to presume a women’s measles im- munity based on known rubella immunity. Thus, pregnant women exposed to measles should be tested and treated if nonimmune.