Rubella specific IgM is detectable in six months after birth or even until one year of age. Its detection is more indicative of pre-natal rubella infection than postnatal infection. In 95% of CRS infants, specific rubella IgG can be acquired after 6 months of age (the age of maternal IgG eradication) (8). Positive IgG antibody after 6 months of age may indicate either prenatal or postnatal infection. The detection of IgG1 (which is low) is diagnosed as prenatal infection (8). The virus can be recovered from the posterior pharynx and conjunctiva, CSF, or urine. In the CSF, the virus may also appear for several years. There are two approaches to serologic diagnosis. Antibody against rubella can be measured in umbilical cord serum. If IgM is found because it is of embryonic origin, the diagnosis is definitive. However, incomplete deletion of IgG (most of which are of maternal origin) or rheumatoid factor can give rise to false positive results. In the early days, the specific Ab titer against rubella may not be high enough to get positive. The second approach is to monitor whether IgG levels remain permanent or not. Maternal Ab has a half-life of 30 days, they decrease by half in one month and disappear in 6 to 12 months. Stable IgG levels at this age, especially at high levels, indicates intrauterine infection with rubella. Serum should be checked at 3, 5 and 6 months and followed with another sample if necessary (9). The availability of specific tests for prenatal diagnosis can facilitate counselling for parents concerned about maternal contact or infection. The use of PCR has recently been suggested. Sampling and the maternal infection time affect test sensitivity, which is 100% in amniotic fluid samples and 83% in chorionic villus samples. Repeat tests can increase accuracy (10).
Some investigations in Iran showed that rubella immunity in women of childbearing age fluctuated between 70% and 95% from 1968 to 1995. The rate of rubella immunity in this population in 1995 was estimated 80%. Therefore, this year in the present study was considered a non-epidemic year. The number of children born with deafness due to rubella would be expected to increase in epidemic years (10).
The present study with the aim of investigating the safety of rubella in the blood of infants (maternal and neonatal immunity) 8 years after the national vaccination in 2011 showed that approximately 75% of infants were immunized and 25% were immune deficient and prone to rubella infection. This will increase the risk of congenital rubella syndrome. According to recent studies, after 8 years of this vaccination program, there has not been a detailed assessment of the maternal-fetal transmitted immunity via cord and placenta (11). In present study of 154 infants, 58.4% of mothers had a history of vaccination in or after national vaccination program in 2003. No IgG immunogenicity was detected in 27.3% of population. This might be due to less number of subjects in this study compared to similar studies.
The mean age in infants with previous immunity and recent infection and group with no immunity and no recent infection was about 4–5 months and was not different. Over time, acute phase IgM antibodies gradually decreased in neonates with congenital infection. Therefore, the elimination of this antibody was expected at the age of 5–6 months. Positive antibody before the age of one year,can be due to intrauterine infection or placental transmission from mother. It may be concluded that infants suspected to have intrauterine infection INTRA UTERINE INFECTION were more prone to intrauterine infection than healthy infants because of lack of maternal protective antibodies (12). Except for cardiac disease, other clinical signs were in favor of congenital rubella infection that showed a marked increase in the group of infections. This indicated the importance of having at least one other symptom (other than heart disease) as an adjunct to the diagnosis of congenital rubella syndrome in infants suspected of Intra uterine infection .
The incidence of congenital rubella in every 100 infants suspected of Intra uterine infection was about 8.1% in our study. It was lower than incidence in Tanzania (12%). There were no cases of congenital rubella in live born babies of healthy infants (13). In this study, the proportion of cases diagnosed with CRS at the beginning of infancy was similar to 34% in the UK under 6 months of age. It is estimated that the prevalence of bilateral hearing loss increases to 1.5–2/1000 children under the age of 6 years [14]. In Iran, the prevalence of hearing loss is 1/1000 children [7]. Regarding the prevalence of SNHL and the estimated AR in this study (12%), congenital rubella was considered as the cause of deafness in approximately 93 children aged 1–4 years of age in the present study. If we assume that the epidemiology of rubella in Tehran, the capital city of Iran, is similar to other areas of Iran, we obtain the estimate that in the year of the present study there were approximately 620 children (1 to 4 years) in Iran with deafness that could have been prevented by rubella vaccination. According to some studies in Iran, congenital rubella is responsible for 12% of cases of sensory neural hearing loss. Nine mothers (41%) of 22 deaf, seropositive children in the present study reported a history of rubella, rash, or rubella exposure during pregnancy. Other studies have also reported between 40% and 75% of deaf seropositive children had such a maternal history (14). In this study, the degree of hearing loss in children who attended deaf educational centres was often higher than 50 dB (severe to profound hearing loss), and their hearing loss was bilateral. Thus, children with low severity of deafness were not included in this study, and the relation between severity of deafness and congenital rubella could not be estimated. About 20% of the children in deaf educational centres were not included because of a history of MMR (Measles, Mumps and Rubella) vaccination, which may lead to an underestimation of the OR. Meanwhile, experience in other countries suggests that if MMR vaccination coverage is less than 60–70%, it may actually increase the age of infection, and therefore the incidence of CRS (14).
All above finding indicate that the prevalence of CRS in Iran is approximately 0.2/1000 (Before rubella vaccination in Iran). According to research done in Iran (during the year of this study), the rate of rubella immunity has reached about 80% (15); however, this rate of immunity is similar to that in other countries during the rubella pandemic of the 1960's, which claimed thousands of victims. Epidemiological evidence had shown that while rubella virus was continuing to circulate among children, there was still a risk of infection in pregnant women, even though only 3% of them were non-immune, and there was little prospect of eliminating CRS (16). If we assume that the epidemiology of rubella in Tehran (capital city of Iran), is similar to other areas of Iran, we obtain the estimate that in the year of the present study there were approximately 620 children (1 to 4 years) in Iran with deafness that could have been prevented by rubella vaccination. he world has now accumulated 35 years of lessons on use of rubella vaccine, and some striking examples of how rubella vaccination strategies should and should not be applied (17). Most importantly, studies in developed countries had generated the following recommended vaccination program: routine MMR vaccination at 12–14 months of age followed by a second dose of MMR vaccine at 4–6 years (both sexes) (7). This study clearly showed the necessity for suitable rubella vaccination program in Iran. However, inadequately implemented childhood vaccination runs the risk of altering rubella transmission dynamics and can lead to increase insusceptibility in women of childbearing age with the potential of increased numbers of cases of CRS. Consequently, it is essential that childhood vaccination programs achieve and maintain high levels of coverage (7,17).