In middle and low-income countries, HAI rates are higher when compared to high-income countries. These differences are mainly related to poverty, lack of basic sanitation and hygiene, lack of adequate equipment, and infrastructure, all of which are associated with the vulnerability of the population involved [1, 4].
However, few studies deeply investigate the potential association of non-biological factors, such as income, education or access to primary care, with HAI acquisition and antimicrobial resistance [8, 9, 10]. In this study we seek to understand the role of hospitalization due to PCSC as a risk factor to HAI.
Our hypothesis was that PCSC could be a marker of social vulnerability leading to unfavorable outcomes during hospitalization. The rationale for this hypothesis is that patients admitted due to PCSC have a history of failures in the effectiveness of primary care, thus accumulating comorbidities, and may be under social deprivation.
Nevertheless, in our casuistic we did not find an association between hospitalizations due to PCSC and acquisition with HAI.
Despite lack of association, our results demonstrated that this phenomenon needs to be better explored. In the group of patients with hospitalizations for PCSC who presented HAI, we observed some noticeable characteristics such as ageing, previous comorbidities, and retirement from work with low monthly family income. Studies indicated that higher rates of re-admissions, mainly in emergency services due to the presence of multiple comorbidities, characterizes some degree of complexity of the population that is hospitalized [11, 12, 13]. This phenomenon may be associated with a counter-transition demographic model, in which advancing population ageing and epidemiological change occur, with an increase in chronic non communicable diseases and climatic diseases, but still with a high incidence of infectious diseases [14, 15, 16].
Among the comorbidities of the studied population, diabetes was very common. Jeon (2014)  points out the presence of this comorbidity in both the population with community infections and HAI. In a recent systematic review of the risk factors for the presence of HAI, the presence of diabetes showed an independent risk factor for the presence of HAI (relative risk of 1.76; 95% CI, 1.27–2.44) .
Other studies demonstrated the influence of some social determinants of health, such as income, education, and housing on the occurrence of other infectious diseases and on re-admissions for chronic and acute diseases [19, 20]. Our study did not identify socioeconomic factors associated with HAI, although the group of patients hospitalized due to PCSC who acquired HAI had slightly (non-significant) lower monthly family income when compared to the group without HAI.
Other studies conducted in the UK in a single cardiology center explored the influence of non-biological issues, such as income and education, and have demonstrated higher risk of presenting surgical site infection for methicillin resistant Staphylococcus aureus among the group of patients from the most disadvantaged socioeconomic areas . In a study conducted by Packer and colleagues (2015)  in Scotland it was found a possible association in the group of patients from regions with higher indices of social deprivation and the prevalence of HAI.
The findings from the literature highlights the need to investigate the influence of these factors for HAI, mainly in countries with greater social inequalities, with probable overlapping of social deprivation, failures in access to primary care, and lack of good structure for the implementation of HAI prevention and control programs . In our casuistic, at least five HAI cases could have been avoided if patients received efficient care at primary level.
Among the limitations of our study, the actual HAI rate was lower than expected during the sampling procedure and may have contributed to reducing the power of sampling and the non-confirmation of the research hypothesis. Also, around 50% of the participants came from the city of São Paulo, and the use of broad socioeconomic indicators (MHDI and Gini index) could be not enough discriminatory for socioeconomic vulnerability in a city that has an unequal distribution of wealth, with several spots of poverty. This study was performed in a tertiary hospital that received referred patients, which may have jeopardized the results.
We conclude that, are still unclear if and how much the HAI rates are influenced by vulnerability conditions such as preventable hospitalization by primary care. However, our study brings contribution for the planning and direction of public actions and policies for the reduction of PSCS and the prevention and control of HAI. The complexity of this phenomenon may require new methods and study designs may to fully capture and understand the impact of primary care in reducing the burden of HAI in the population.