Sexually transmitted infections (STIs) are a major public health challenge, particularly in developing countries where the health infrastructure is often poor (Marshall et al. 2009). Generally it is reported that at least one million people are infected with curable STIs each day worldwide of which at least 10% of these cases are from sub-Saharan Africa (Newman et al. 2015; Seidu et al. 2020; Torrone et al. 2018; World Health Organization 2016). However, when left untreated, STIs may lead to acute diseases such as cervical cancer and pelvic inflammatory disease, infertility, and sometimes death (Jung 2019; Naidoo et al. 2014). Sexually transmitted infections may cause adverse birth outcomes and mother-to-child transmission as well as other severe reproductive health issues in pregnant women (Kurewa et al. 2010). Furthermore, STIs have been shown to increase the transmission and acquisition of the human immunodeficiency virus (HIV) (Reynolds et al. 2006).

The incidence of STIs is often influenced by structural factors such as economic, political, social, and organisational environments that define the context of the STI risk in the population (Marshall et al. 2009). For example, several studies have shown that poor health infrastructure, high cost of healthcare, lack of STI surveillance systems, poor sexual health knowledge and practices, and migratory behaviours are associated with high STI incidences in sub-Saharan Africa (Chirwa 2020; Kurewa et al. 2010; Mohammed et al. 2019; Nunu et al. 2020; Olusola et al. 2019). Previous studies have found that sex workers and truck drivers were the high-risk groups for STIs as they often have multiple sex partners and are unprotected (Botão et al. 2016; Makhakhe et al. 2017). Urban centres along trade routes are important hotspots of high STI incidence because sex workers are often concentrated along trade routes used by truck drivers (Delany-Moretlwe et al. 2014; Gysels, Pool & Bwanika 2001). However, there are few studies that document the risk factors associated with high STI incidences in port of entries and exits between countries.

Beitbridge town in Zimbabwe is an important trade route connecting South Africa to several countries north of Limpopo such as Zimbabwe, Zambia, and Malawi. Previous studies have shown that increase in knowledge and access to sexual health centres were effective in reducing STI incidences (Boyce, Katz & Standley 2019; Bunnell et al. 1999; Chirwa 2020). Interestingly, the STI incidences increased in Beitbridge despite the surge in collaborative STI prevention programmes spearheaded by non-governmental organisations, the local government, and the Ministry of Health and Child Welfare (Figure 1). For example, since 2016, several 24-h wellness centres for STI treatment and testing were established around the town while STI awareness campaigns were intensified. The aim of this study was to assess the risk factors associated with the high STI incidence in Beitbridge, Zimbabwe.

The study found that the nature of employment was a significant factor that contributed to the high incidence of STIs. Those that were not formally employed had to find other sources of livelihoods of which prostitution was one of them. These findings are supported by Hunter (2007) in a study that was conducted in South Africa which reported that prostitution is one of the sources of livelihoods particularly in unemployed women (Hunter 2007). These findings agree with that of previous studies in Uganda (Gysels et al. 2001), South Africa (Makhakhe et al. 2017; Naidoo et al. 2014), and South Korea (Jung 2019) that found an association between prostitution and poverty. The unemployment rate in Zimbabwe is estimated at above 90% and this results in most people pursuing informal trades including sex work (Mujeyi & Sadomba 2019).

The area of residence was also significantly associated with the high incidence of STIs as the odds were 2.78 times more likely that the cases were residing in Dulibadzimu residential area as compared to other suburbs. Dulibadzimu is the only high-density suburb in Beitbridge. Most people in Beitbridge stay in Dulibadzimu because it has cheaper accommodation. These findings are reinforced by Evans and Saegert (2000) who found that low-income families tend to crowd in high-density suburbs that are affordable.

A larger proportion of the controls were knowledgeable as compared to the cases. It has been reported that knowledge about STIs plays an important role in mitigating its impacts (Hemalatha et al. 2011). Knowledgeable people are bound to take necessary steps in preventing themselves from contracting STIs (Hemalatha et al. 2011). On the other hand, lack of knowledge on STIs places one at a higher risk of contracting STIs (Hemalatha et al. 2011) as evidenced by the higher proportion of cases who were not knowledgeable as compared to the controls in our current study. The cases were 7.56 times more likely to have slept with at least two sexual partners. Having multiple sexual partners increases the risk of contracting STIs (Rosenberg et al. 1999). The more the number of sexual partners the higher the risk of contracting and spreading of STIs (Rosenberg et al. 1999). Different studies have reported that being faithful to one sexual partner reduces the risk of contracting and spreading of STIs (Desiderato & Crawford 1995; Joffe et al. 1992; Setswe 2007).

The cases were 22 times more likely to demand money for sexual activities as compared to the controls. The same cases were 3.7 and 2.86 times more likely not to use a condom and consume alcohol, respectively. Most of the cases were engaged in prostitution which is usually associated with risky sexual behaviours and consumption of alcohol (Cusick 1998; Gossop et al. 1995). Furthermore, our study found that the cases were 15.5 times not to suspect that their partners were promiscuous. This shows that they do not really care what their partners do out there as most have transactional sex and multiple partners (Sato 2016). They only care about whether their needs are taken care of (Sato 2016).

In conclusion, this study found that the nature of employment, knowledge of STIs, area of residence, multiple sexual partners, transactional sex, failure to use condoms, alcohol consumption and failure to care about sexual partners’ activities were significantly associated with a high incidence of STIs. Therefore, there is a need to conduct intense awareness campaigns regarding the risk of having multiple sex partners, and about alcohol intake management, and safe sex practices such as condom use. It is evident that abstinence is not possible for those who depend on proceeds from sexual activities. Therefore, safe sexual practices should be encouraged.