To our knowledge, this is the first study to thoroughly examine the impact of migration-related characteristics on the prevalence of CMV, TOX, and RV infections among women of childbearing age with an unprecedentedly large dataset of over 2.4 million samples in southern China. Overall, compared with native women, migrants had a higher prevalence of recent TOX infection, past CMV infection, and RV infection by natural ways, but a lower risk of past TOX infection suggesting a healthy migrant effect. We also found that inter-provincial migrants had a lower risk of past TOX infection but a higher risk of recent TOX infection and past RV infection than intra-provincial migrants. Having a migrant spouse for migrant women further amplifies the risk of TOX, CMV, and RV infections. This study helps to formulate tailored intervention programs for preventing prenatal infections and improving maternal and infant health in this resource-constrained setting.
Migrant status and TORCH infections
Surprisingly, migrant women showed a lower risk of past TOX infection as compared with native women, which could be explained by several mechanisms connected to the healthy migrant effect (HME). Previous studies observed significant regional variations in the prevalence of human TOX infection with the trends increasing from West China to East China, which coincided with the incidence of TOX infection in food animals [24, 25]. As an economically developed province, Guangdong has attracted a huge number of migrant populations from the less developed central and western regions. Migration connected areas of low and high risk, leading to the lower prevalence of past TOX infection among migrants. Meanwhile, the fact that people with better health status are led to migrate might also explain this protective effect. However, a higher infection risk of recent TOX infection among migrants than natives was found in this study. This implied that the healthy migrant effect might be offset as individuals acculturate to local customs in the new host place. The adoption of negative lifestyle factors such as eating raw seafood in Guangdong might increase potential exposure to infectious agents [26, 27]. These findings implied that migrants were at high risk of TOX acquisition after coming into Guangdong. Thus, reducing the transmission from local sources of infection to migrants might play a critical role in the prevention of primary TOX infection during preconception.
Unlike TOX infection, there was little support for the existence of an HME when it comes to CMV and RV. We identified a higher rate of past CMV infection among migrant women, which was consistent with several previous findings [28, 29]. This might have been attributed to the transmission of infection through physical contact and increased sexual risk behaviors during the migration process [30, 31]. In addition, this study found that migrant women had a lower vaccination rate of RV and were more prone to have a past infection of RV by natural ways. Previous studies have reported the insufficient utilization of health care services among migrants than general populations due to restrictive health-related policies, poor economic conditions, and the lack of awareness of seeking medical services [32, 33]. Migrants were often overlooked for the RV vaccine catch-up immunization programs and their immunity was often acquired by natural infection [34]. Therefore, immunization strategies targeting migrants were urgently needed, which proved beneficial in preventing the spread of infection and guaranteeing migrant health in the European countries [35].
Migration distance and TORCH infections among migrants
In terms of the impact of migration distance on the infection risk of TOX, this study discovered that inter-provincial migrants had a lower risk of past infection but a higher risk of recent infection than intra-provincial migrants. This finding, similar to the results about the impact of migrant status, further implied that the burden of TOX infection may be predominantly attributed to local parasite prevalence, dietary habits, and cultural habits, rather than the importation of latent infections acquired by migrants from other provinces. The abundant natural water network and ample annual precipitation in Guangdong possibly help the oocyst spread and retain accessible for potential hosts [24], posing threat to susceptible women like inter-provincial migrants. Moreover, inter-provincial migrants were more prone to be infected with RV in natural ways than intra-provincial migrants. The literature on the immunization status of RV among rural Chinese women pointed out the relatively high RV vaccination rate in Guangdong than elsewhere [36]. A reduction in the force of infection due to vaccination partly restrained the acquisition of RV infection among intra-provincial migrants.
The spouse’s migrant status and TORCH infections among migrants
Insight on how the spouse’ migrant status influences TORCH infections among migrant women have not been studied as extensively. One previous study on maternal CMV serostatus in early pregnancy suggested that both maternal and paternal migrant status have been reported to be correlated with the presence of CMV-specific IgG antibodies in the maternal serum and there was also an interaction between them [37]. Similarly, this study indicated that migrant women had a greater risk of TOX, CMV, and RV infections when their spouses also were migrants. Reports of the presence of TOX, CMV, and RV in semen, saliva, and cervical secretions and several lines of epidemiological evidence have suggested that sexual activity facilitates the transmission of the above pathogens [38–40]. Besides, women whose spouses were migrants were significantly at higher risk of being infected with sexually transmitted diseases [17, 18, 41]. Thus, it is plausible that among migrant women, the infection of TOX, CMV, and RV may also be affected by their spouse’s migrant status, which suggested that interventions targeted at the spouse of childbearing aged women are also an essential part of managing TORCH infections.
Strengths and limitations
Relying on the NFPHEP, this study has reliable data, a large sample size, and good sample representation, allowing us to perform a convincing comparison between different populations. Moreover, this study thoroughly assessed the native-migrant gaps in the prevalence of TOX, CMV, and RV infections and emphasized the role of migrant distance and the spouse’s migrant status in the disease transmission. From the broader public health perspective, this study helps to develop effective responses to improve maternal and infant health. Identifying vulnerable women of childbearing age can guide the implementation of targeted screening strategies and prophylaxis measures.
There are several limitations to this study. Firstly, the exact time of the acquisition of TORCH infections cannot be determined. Considering that only migrant women, who have stayed in the locale for at least 6 months, met the inclusion criteria of NFPHEP, it’s plausible to recognize the presence of IgM antibodies as the active or recent infection happened in the hosting place. But as for the presence of IgG antibodies, it’s hard to distinguish the specific phrase of infection acquisition. Secondly, sociodemographic information and vaccination history of RV were self-reported and may be subject to measurement error. Thirdly, a cross-sectional design for this study cannot establish causality between migration-related characteristics and TORCH infections. But standardized laboratory TORCH testing enables us to identify more precisely the prevalence of infection among native and migrant women. Finally, other TORCH pathogens, such as HSV and syphilis were not included in this study.