Rubella in children and adults is a mild disease that rarely causes complications: purpura, arthralgia, perivenous encephalitis, and, very rarely, PESS unrelated to the measles virus [1]. However, it should be noted that many primary rubella infections do not present with clinical signs and may go unnoticed, particularly in pregnant women, hence the importance of diagnosis [2]. During pregnancy, congenital rubella corresponds to fetal damage during a maternal primary infection in the first 20 weeks of pregnancy; the earlier it occurs, the more severe it is. This infection can lead to serious fetal complications, collectively referred to as congenital rubella syndrome (CRS). This syndrome can affect the heart (patent ductus arteriosus), the ear (deafness), and the eye (cataracts). In addition to the effects on embryogenesis, there is also fetopathy, which is a consequence of the virus multiplying in the tissues: hepatitis encephalitis, thrombocytopenic purpura, bone lesions [1][3][4]. The rubella virus is a teratogenic pathogen, responsible for 2% to 3% of congenital malformations in fetuses of infected mothers [5]. By January 2024, 175 out of 194 countries had introduced the rubella vaccine, and global coverage was estimated at 69%. Reported cases of rubella have fallen by 97%, from 670,894 cases in 102 countries in 2000 to 17,865 cases in 78 countries in 2022 [6]. In Africa, more than 100,000 children are born with congenital rubella syndrome (CRS) each year, particularly in resource-limited countries, and the continued circulation of the virus still exposes many non-immune pregnant women to a high risk of infection [7].

In the Republic of the Congo, although serological screening for rubella is routinely prescribed during prenatal visits, epidemiological data on rubella and its risk factors among pregnant women remain limited or even outdated, particularly in urban areas, where population density and mobility facilitate the transmission of infectious diseases [8][9]. In light of this observation, the present study was conducted to determine the prevalence and risk factors for rubella among women attending prenatal checkups at hospitals in the city of Brazzaville.

The rubella virus is a significant public health problem and is primarily responsible for congenital infections, which cause serious birth defects. Humans are the only known hosts. Transmission requires close contact between individuals [2][6].

Our study focused on rubella infection and immunity in pregnant women attending prenatal consultations at three integrated health centers in Brazzaville, namely Bissita, Nkombo Matari, Jeanne Vialle, and the Plateau Medical-Social Center.

The methodology used consisted of analyzing plasma samples by TROD and ELISA for all women to determine prevalence in order to confirm the diagnosis.

This study was conducted among 124 pregnant women. The results revealed that the average age of these women was 28 ± 5.96 years (Min-Max: 15 - 41 years). This average was relatively close to that obtained by Makemgue et al. in Chad and Nadesh et al. in Cameroon in a population of pregnant women attending consultations [5][10]. A study in Nigeria conducted by Olajide et al. also reported an average age close to ours [11]. However, in a study of pregnant women in Nigeria, the average age was 30.5 ± 7.9 years [12]. This difference may be due to the variability in the size of their sample and the study population, which consisted of women of childbearing age who may or may not have attended prenatal consultations.

We found that the population in our study was aged between 15 and 41 years. Numerous studies have reported the same age range [5][7]. The similarity with these studies can be explained by the fact that women in this age group are sexually active. The majority of pregnant women had a secondary education level, but some studies, such as those conducted in Nigeria by Bola et al. and Olajide et al., had a study population with a higher education level [11][13]. These results, when compared with those studies, confirm that women’s education in the Republic of Congo is declining, as reported in the sectoral education strategy [14]. In this study, we observed that the age of pregnancy was in the second trimester, as reported in several studies [5][10]-[12]. However, a few studies reported the age of pregnancy in the first and third trimesters [13][15].

The point prevalence of detectable rubella virus infection in our study was 78.22%, or 76.61% for IgG and 1.61% for IgM. We therefore found that the majority of women in this study were immune to the rubella virus, while only 1.61% were not. Some studies have reported higher prevalences of IgM than ours, ranging from 3% to 38.5% in Africa and Asia [10][11][13][15][16]. Comparing our results with those of these authors, this difference may be explained by poor hygiene or ventilation conditions and overcrowding. In addition, the 1.61% were women in their first trimester, indicating a recent infection prior to prenatal care. What is positive in this study is the fact that the majority of pregnant women had IgG carriage of the infection, which indicates good immunization. This high rate is reported in several studies conducted on pregnant women around the world, in Africa and in Congo (see study by Mieret et al.), showing good immunization [8][10][17][18]. Our prevalence is below the World Health Organization’s recommendation that at least 90% - 95% of women of childbearing age be immunized in order to eliminate rubella. In fact, our prevalence is between 70 and 85% for IgG, which, according to the WHO, translates into low to moderate immunity that is insufficient to prevent chains of transmission [6]. While some studies have established a link between rubella infection and age, environment, and marital status, the present study has highlighted an association between rubella carrier status and the first trimester of pregnancy [5][12][19]. Our results are consistent with those reported by Bola et al. and Makemgue et al. regarding gestational age [5][13]. In fact, women in the first trimester of pregnancy had a higher risk of rubella infection than those in the second trimester (ORc: 0.35 [0.13, 0.91]; p = 0.028) and the third trimester (ORc: 0.22 [0.05, 0.87]; p = 0.023).

This study revealed that the rubella virus is indeed present in the population of pregnant women in our country and that low IgM levels—indicating a recent infection—pose a risk to the fetus or child. The significant association between the first trimester of pregnancy and viral shedding—which indicates an increased risk of infection—should enable us to strengthen preventive measures among women of childbearing age, particularly through vaccination before pregnancy.

This study was conducted in accordance with the ethical guidelines governing research involving human subjects in the Congo and the Declaration of Helsinki. Administrative approvals were obtained from the administration of Djiri General Hospital (No. 216-1/MSP/DGHGD), the integrated health centers, and the Ethics Committee for Health Sciences Research (CERSSA) (No. 033-40/MESRSIT/DGRST/CERSSA/-25). All parents or guardians of minors, as well as the participants, provided their informed consent by signing a consent form. The confidentiality and anonymity of the information provided were guaranteed.

The authors declare that no generative AI technology such as large language models (ChatGPT, COPILOT, etc.) and text-to-image generators were used in the writing of this manuscript.

We are very grateful to all the pregnant women who agreed to participate in the study, as well as to the heads of the health centers and their respective staff.

Not applicable. However, all authors have given their consent for the publication of this manuscript through their respective emails.

Conceptualization: Roch Bredin Bissala Nkounkou; Methodology: Roch Bredin Bissala Nkounkou, Paola Candyse Tsimba Lemba, and Raphaëlle Francia Moyen; Statistical analysis: Dorcas Mouyama; Data entry: Esther Nina Ontsira Ngoyi and Luc Magloire Anicet Boumba; Review and editing: Gickelle Mpika Bintsene and Henri Essome; Supervision: Carole Else Eboumbou Moukoko; Fieldwork: Roch Bredin Bissala Nkounkou and Dorcas Mouyama.