INTRODUCTION

Rubella, commonly known as German measles is an infection caused by the rubella virus, a positive-sense RNA virus of the Rubiviridae family. It is an acute viral communicable disease mainly of children, young adults, women of reproductive age and pregnant population. The virus is transmitted via droplet infection from the upper respiratory tract of infected person.^1,2 Following an incubation period of 14-21 days, the disease which is usually mild, self-limiting and with usually no consequences develops.²

Rubella infection in the non-immune pregnant woman especially within the first twenty weeks is associated with 90% chance of trans-placental transfer to the foetus.^2,3 This can result in spontaneous abortion, intrauterine growth restriction or in-utero foetal demise.⁴ Furthermore, the new born can have congenital Rubella syndrome (CRS) which is a constellation of bilateral sensorineural deafness, cataract, mental retardation, microcephaly and congenital heart defects among others.^4,5,6

The burden of CRS is not evenly represented in most countries.³ In the USA, approximately 20,000 cases were reported between 1964-1965 during an outbreak.³ The cost of the treatment is estimated to be 220,000 US Dollars per case.⁷ To curb this ugly trend, concerted effort was made to forestall future epidemics via widespread vaccination campaign across USA, Latin America and Europe while the year 2010 was earmarked for elimination of rubella infection and fresh cases of CRS across these regions.³ In contrast, data from the World Health Organization (WHO) estimates more than 100,000 cases of CRS per annum in developing countries alone.⁸ Many of these countries are yet to imbibe prevention and vaccination programs against rubella. In addition, where such programs exist, the immunization cover is sub-optimal. Consequently, rubella infection in pregnancy still occurs with CRS often diagnosed in the post-natal life. In 2000, a WHO position paper on rubella vaccines recommended that all countries asses her rubella prevalence and accordingly make plan for the introduction of rubella vaccine.⁹

Screening and vaccination of women and children against rubella is neither part of routine antenatal tests nor among the vaccine-preventable diseases in the National Program on Immunization (NPI) in Nigeria.^10,11 Rubella infection and CRS are also not notifiable in the country yet it is preventable. The national prevalence of Rubella in pregnancy as well as of CRS is not known. However there has been pockets of report in the last two decades from a few centres across Nigeria.^10,11 Despite all these studies, information from the southeast is scarce.

Rubella infection during the first and early second trimesters in the sero-negative is associated with deleterious foetal effects including CRS. Some antenatal women may present with rash, which may not be attributable to the infection. Furthermore, information on the prevalence of the infection in pregnant women is scarce especially in Umuahia and its environs. Nigeria is also a low resource country hence the dire need to judiciously use available scarce resources. To this end, obtaining government patronage for intervention should be evidence-based. Thus, the necessity to determine the sero-susceptibility of Rubella infection in pregnancy and the prospect of having an organized prevention program including Rubella vaccine is the justification for this study.

MATERIALS AND METHODS

Study area

The study was performed at the antenatal clinic of Federal Medical Centre (FMC), Umuahia and the serology department of MECURE diagnostic centre, Umuahia, South East Nigeria. MECURE diagnostic centre is in partnership with the Abia State Government. The Study population consisted of pregnant women who attended the antenatal clinic of the hospital who accepted on their volition to participate and were consecutively recruited. Pre-tested structured questionnaires were given to the participants and relevant data collected. The appropriate sample size was calculated using the formula below, which was suitable for cross-sectional studies with qualitative variables:

N = Z² [P (1-P)]/x². From the formula above, the appropriate sample size is 245. When we considered additional 10% for contingencies including participant withdrawal from the study and recording error, the sample size was 270. Approval was obtained from the Health Research Ethic Committee (HREC) of FMC Umuahia. This study was carried out over a four-month period between February and May, 2016.

About 5ml of venous blood sample was taken from the ante-cubital fossa of each participant under strict aseptic condition and were put in a plain container and left standing for at least 1-2 hours to allow for clot retraction or centrifuged at 1500 revolution per minute. The obtained sera were saved in the laboratory at 4-8⁰C and analysed in batches within 10 days. Reagents for the analysis were ready to use and were manufactured and provided by ROCHE diagnostics. Rubella 1gG antibodies were determined in collected sera using fully automated ELECSYS 2010 (ROCHE diagnostics). The data was entered and analysed using the statistical package for social science (SPSS) version 20. Descriptive statistics which includes mean and standard deviation were used to summarize continuous numerical variables like age and 1gG level while categorical variables were summarized using frequency and percent. The association between categorical variables was done using Chi-square testing. A P-value of <0.05 was considered statistically significant. Results were presented in tables and chart.

RESULTS

Two hundred and fifty-seven pregnant women took part in this study over a period of four months. Table 1 shows the socio-demographic characteristics of the subjects. The age range was 16-42 years, with a mean of 30.56 (± 4.86). Majority (68.5%) were between the ages of 25-34 years. Most (98.8%) were of the Ibo tribe. The participants in the urban area (51.4%) were almost equal in number to their rural counterpart (48.6%). The proportion of women seemed to decrease with increasing parity. Nulliparous subjects had 41.4% while grand multiparae made up 2.3% of cases. Most of the participants were in their second trimester (59.1%). A greater proportion was married (98.4%), public servants (42.4%) and had post-secondary education (71.2%). All were Christians and had no previous rubella vaccination.

The serum immunoglobulin G (1gG) level ranged from 0 – 512 IU/ml. The mean titre was 153.2 IU/ml (±142.2). Table 2 shows serum 1gG in the study subjects. Most of the women (92.2%) were seropositive for rubella 1gG antibodies with level greater than 10iu/ml while 7.8% were sero-negative with less than or equal to 5iu/ml. None of them had borderline assay. Figure 1 shows that the sero-prevalence of rubella 1gG antibody in this study is 92%. All those aged 19 years or below had rubella 1gG antibody (positive). The proportion was lowest among those at least 40 years old (85.7%) while other age groups had between 87.5% and 96.2% (Table 3). This was however not statistically significant (X² = 3.536, P=0.618).

Furthermore, we found that all the women with a parity of four or more were Rubella-IgG positive (Table 4). This difference was not found to be statistically significant (X²=3.125, P=0.681). There was no association between rubella antibody and gestational age of the subjects in this study as shown in table 5. The number of women in 2^nd and 3^rd trimester were similar (92.8% vs 92.3%) while 88.9% were in their first trimester. This again showed no statistical significance (X²=0.481, P=0.786). Among those who were positive, 92% had secondary or more level of education as shown in table 6. Statistical testing was not significant (X²=0.204, P=0.903). The rural subset of the population sample was almost equal to the urban counterpart (92%) as highlighted on table 7. There was also no significant statistical association (X²=0. 016, P=0.899).

 Table 1: Demographic characteristics of the subjects.

Table 2: Serum IgG levels in study subjects.