Sex, Age, and Comorbidities Are Associated with SARS-CoV-2 Infection, COVID-19 Severity, and Fatal Outcome in a Mexican Population: A Retrospective Multi-Hospital Study

People with comorbidities and the male sex are at a higher risk of developing severe COVID-19. In the present study, we aim to investigate the associated factors for infection, severity, and death due to COVID-19 in a population from Nuevo León, México. Epidemiological COVID-19 data were collected from 65 hospitals from December 2020 to May 2022. A total of 75,232 cases were compiled from which 25,722 cases were positive for SARS-CoV-2. Male sex, older age, diabetes, obesity, and hypertension were associated with infection. In addition to the above-mentioned factors, renal disease, cardiovascular disease, and immunosuppression were found to be associated with increased COVID-19 severity. These factors, as well as neurological diseases, are also associated with death due to COVID-19. When comparing the different variants of SARs-CoV-2, the variant B1.1.519 increased the probability of death by 2.23 times compared to the AY.20 variant. Male sex, older age, diabetes, obesity, and hypertension are associated with SARS-CoV-2 infection, severity, and death. Along with the aforementioned comorbidities, renal disease, cardiovascular disease, and immunosuppression are also associated with severity and death. Another factor associated with death is the presence of neurological disease. The SARS-CoV-2 B1.1.519 variant increases the odds of death compared to the SARS-CoV-2 AY.20 variant.


Introduction
The world is recently recovering from the COVID-19 pandemic, a disease that originated in the seafood market located in Wuhan, Hubei, China. Since the first case in 2019 up to October 2022, more than 6 million lives have been lost and there are 755,703,002 COVID-19 confirmed cases [1]. The virus responsible for this disease is of the coronavirus type and is now termed SARS-CoV-2. Patients with the mild disease most commonly displayed a cough, hyposmia, and sputum with fever only present in around 11% of patients [2]; patients with severe COVID-19 displayed dyspnea and commonly present comorbidities [3]. Patients with the critical disease had respiratory difficulties, acute cardiac lesions, and multiple organ failure [3]. 2

of 10
At the beginning of the pandemic, male sex, age, and several comorbidities were associated with an increased risk of severe COVID-19, such as hypertension, diabetes, renal disease, chronic obstructive pulmonary disease (COPD), autoimmune diseases, and cancer [4][5][6][7][8]. In Mexico, COVID-19 vaccination started in December 2020 and the administration was in stages according to priority groups with vaccines varying in type upon availability [9]. By June 2022, a total of 209,673,612 vaccines were administered [10]. Furthermore, by that time, 91% of the population over 18 years old had at least one dose and a booster dose was already being administered to the same population group [10]. By June 2022, one dose of the COVID-19 vaccine had already been administered to 55% of adolescents (12 to 17 years of age) [10]. In the present study, we analyzed epidemiological data of a population from the northeast of Mexico, where we report the associated factors of infection, severity, and outcome of COVID-19 disease.

Database and Data Depuration
A database containing information about the patients that required COVID-19 testing from 18 December 2020 to 7 April 2022 was obtained. The database comprised a total of 448,367 cases from 65 hospitals distributed in Nuevo León, Mexico. Out of 448,367 cases, 25,787 (5.8%) were COVID-19 positive, determined using quantitative polymerase chain reaction (qPCR), and the variant determination was performed by the Instituto de Diagnóstico y Referencia Epidemiológicos (InDRE), Secretaria de Salud, Mexico, as approved by the World Health Organization [11]. Cases with incomplete data and positive cases for other viruses were excluded from the analysis. A total of 75,232 cases were analyzed (Figure 1). [2]; patients with severe COVID-19 displayed dyspnea and commonly present comorbidities [3]. Patients with the critical disease had respiratory difficulties, acute cardiac lesions, and multiple organ failure [3].
At the beginning of the pandemic, male sex, age, and several comorbidities were associated with an increased risk of severe COVID-19, such as hypertension, diabetes, renal disease, chronic obstructive pulmonary disease (COPD), autoimmune diseases, and cancer [4][5][6][7][8]. In Mexico, COVID-19 vaccination started in December 2020 and the administration was in stages according to priority groups with vaccines varying in type upon availability [9]. By June 2022, a total of 209,673,612 vaccines were administered [10]. Furthermore, by that time, 91% of the population over 18 years old had at least one dose and a booster dose was already being administered to the same population group [10]. By June 2022, one dose of the COVID-19 vaccine had already been administered to 55% of adolescents (12 to 17 years of age) [10]. In the present study, we analyzed epidemiological data of a population from the northeast of Mexico, where we report the associated factors of infection, severity, and outcome of COVID-19 disease.

Database and Data Depuration
A database containing information about the patients that required COVID-19 testing from 18 December 2020 to 7 April 2022 was obtained. The database comprised a total of 448,367 cases from 65 hospitals distributed in Nuevo León, Mexico. Out of 448,367 cases, 25,787 (5.8%) were COVID-19 positive, determined using quantitative polymerase chain reaction (qPCR), and the variant determination was performed by the Instituto de Diagnóstico y Referencia Epidemiológicos (InDRE), Secretaria de Salud, Mexico, as approved by the World Health Organization [11]. Cases with incomplete data and positive cases for other viruses were excluded from the analysis. A total of 75,232 cases were analyzed ( Figure 1).

Statistical Analysis
Categorical variables were described in frequencies. For non-categorical variables, means and standard deviation were calculated. The association of SARS-CoV-2 infection, severity and outcome to sex, age, comorbidities, and tobacco smoking was evaluated using the chi-square test. This was followed by stepwise multivariate logistic regressions for infection and outcome analyses and stepwise multivariate logistic ordinal regression models for severity analysis. In all models, the independent variables were sex, age, comorbidities, and smoking. The severity variable was constructed by categorizing COVID-19-positive patients into mild, severe (diagnosed pneumonia), and critical (required admission to an Intensive Care Unit [ICU] and/or endotracheal intubation).

Characteristics of the Studied Population
A total of 75,232 cases were analyzed, of which 87% were reported as unvaccinated. The mean age was 43.6 ± 20.6 years. Comorbidities were present in 31.5% of the population where hypertension, obesity, and diabetes were the most common. Patients with two comorbidities represented 9.6%, whereas patients with more than two comorbidities represented 6

Associated Factors with SARS-CoV-2 Infection
Several factors are associated to SARS-CoV-2 infection, such as male sex, older age, having diabetes, obesity, hypertension, and presenting two comorbidities ( Table 2). A reduction in the odds of infection within patients with renal disease, COPD, other not disclosed comorbidities, and more than two comorbidities was observed. Tobacco smokers also showed a decreased probability of infection (Table 2). Table 2. Associated factors with SARS-CoV-2 infection (n = 75,232).

Associated Factors with Critical COVID-19
A multivariate analysis was performed to determine factors associated with severe/critical COVID-19 patients, who were hospitalized patients that required either ICU attention or endotracheal intubation. Comparable to factors associated with infection, a group of variables, such as male sex, older age, diabetes, obesity, hypertension, cardiovascular disease, renal disease, immunosuppression, and other comorbidities, were associated with severe/critical COVID-19. Tobacco smoking shows significantly reduced odds of severe/critical COVID-19 (Table 3).

Associated Factors with Death as an Outcome of SARS-CoV-2 Infection
An increased probability of death as an outcome of SARS-CoV-2 infection was found in the male sex, older age, patients with hypertension, obesity, diabetes, cardiovascular disease, renal disease, immunosuppression, neurological diseases, other non-described comorbidities, and having two or more comorbidities. Interestingly, tobacco smoking reduced the odds of death (Table 4).

COVID-19 Variants and Their Association with Death as an Outcome of COVID-19
SARS-CoV-2 variant information and multivariate regression analysis estimated an increase of 2.23 times the probability of death when the infecting variant was B.1.1.519 compared to AY.20 (Table 5).

Discussion
The current manuscript describes the clinical manifestations of COVID-19 in the northeastern Mexican population, where analyses were performed to determine the factors associated with infection, as well as the severity of COVID-19, and death as an outcome of this disease from an epidemiological database from 2020 to 2021. The statistical analysis confirms the association with increased infection odds, severity, and death probability in patients with comorbidities, such as obesity, diabetes, COPD, kidney disease, cardiovascular disease, immunosuppression, and neurological disease, as well as demographic characteristics, such as male sex and older age.
A recent analysis described factors associated with hospitalization and death in SARS-CoV-2-positive patients, where comorbidities were pointed out as associated factors. However, specific comorbidities were not further described [12]. In the present study, we considered SARS-CoV-2-positive patients to be only those with a confirmed PCR test, whereas Loza and colleagues (2022) considered positive to be those with a positive antigen test or a positive result ruled by epidemiologic association, with an increased probability of analyzing COVID-19 negative patients as positives [13,14].
Particularly, a recent study reported male sex, age, and comorbidities as risk factors for SARS-CoV-2 infection, pneumonia, intubation, and death in data collected from 11 February 2020 to 24 September 2020 with a total of 35,476 positive cases from a Mexican northeastern population [15]. By comparing periods of time analyzed by Hid-Cordero and colleagues (2021), the predominant SARS- CoV-2 variant was B.1, B.1.1, and B.1.1222, whereas, during the period studied in the present investigation, the predominant variants were delta (AY.20), followed by B.1.1.519.
Among the associated factors to infection, severity, and death; sex has been one of the characteristics of the population previously described, where males have more prevalence and mortality due to COVID-19 [16,17]. Some theories have come forward to explain sex differences regarding the immune system, where women experienced a stronger immune response compared to men [17]. Sexual hormones may also have a role in COVID-19 severity since it has been shown that estrogens are immunostimulants, whereas testosterone has immunosuppressive effects [18]. Furthermore, the ACE-2 receptor, which is responsible for the binding and internalization of the viral particles of SARS-CoV2 [19], can be induced by testosterone in lung cells, whereas estrogens demonstrated a trend toward a reduction in ACE-2 in lung cells [20].
Another factor, which has been previously associated with severe COVID-19 is tobacco smoking [6]. Smoking was very interesting to investigate in the Mexican population given that according to data from 2016, there were more smokers in the male population compared to females, with 36.6% and 15.5%, respectively [21]. Therefore, this was a lifestyle condition, which could be expected to predispose Mexican men to severe COVID-19. However, smoking was not positively associated in any of the analyses that we performed and the contrary phenomenon was observed, where smokers had a decreased probability of infection, severity, and death; this result has also been reported before [4,12,15]. An explanation for this could be that nicotine can have immunomodulatory and anti-inflammatory effects. Furthermore, tobacco use increases nitric oxide production in the lung which results in a reduction in viral replication and impaired viral entry into the host cells [22]. Within the renin-angiotensin system (RAS), ACE-2 can be found and nicotine can increase angiotensin-I, which in turn, causes a reduction in ACE-2 in the lung; this has been demonstrated in animal models [23]. Nicotine has been suggested as a therapeutic agent to prevent SARS-CoV-2 infection [24].
Old age has also been associated with severe COVID-19 [25]. The COVID-19 lethality rate increases with age, and this has been demonstrated in studies from different countries [26][27][28][29]. In the present study, this association is confirmed, and older age is associated with an increased risk of infection, critical COVID-19, and risk of death.
We have also collected information about variants and their association with death as an outcome of COVID-19. We have shown that there is an increased predisposition to death in people infected with the B.1.1.519 SARS-CoV-2 variant, which has been previously shown [42].
Some limitations of this study consisted of the fact that many data were not considered due to incomplete or wrong information. This may be due to the saturation of hospitals and the prioritization of patient care during the emergency, rather than the data collection. There was no data analysis performed in the current study regarding vaccination. However, only 13% of the studied population reported at least one dose, which is very low compared to the country's vaccination reports. This same situation is noticeable regarding comorbidity reports, given that only 8% of the studied population reported obesity and Mexico has one of the highest obesity rates. Another limitation is the registration of variant information, and this could be due to delays in protocol validations and algorithms established by the national epidemiological surveillance system, which determines that only certain samples are genotyped.

Conclusions
Sex, age, and comorbidities, such as diabetes, obesity, and hypertension are factors associated with SARS-CoV-2 infection. In addition to these factors, renal, cardiovascular, and immune diseases are associated with increased severity and death. Neurological disease is associated with death due to COVID-19. Compared to the SARS-CoV-2 AY.20 variant, the B.1.1.519 variant significantly increased death as an outcome.

Data Availability Statement:
The data that support the findings of this study are available upon reasonable request from the corresponding author, but restrictions apply to the availability to these data, which were used under license for the current study, and so are not publicly available.

Conflicts of Interest:
The authors declare no conflict of interest.