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SARS-CoV-2 has spread throughout the world since 2019, changing in its genome and leading to the appearance of new variants. This gave it different evolutionary advantages, such as greater infectivity and/or a greater ability to avoid the immune response, which could lead to an increased severity of COVID-19 cases. There is no consistent information about the viral load that occurs in infection with the different SARS-CoV-2 variants, hence, in this study we quantify the viral load of more than 16,800 samples taken from the Mexican population with confirmed diagnosis of COVID-19 and we analyze the relation between different demographic and disease variables. We detected that the viral load caused by different variants differs only in the first two days after the onset of symptoms, being higher when infections are caused by the delta variant and lower when caused by omicron. Furthermore, the viral load appears to be higher in outpatients compared to hospitalized patients or in cases of death. On the other hand, no differences were found in the viral load produced in vaccinated and unvaccinated patients, nor did it differ between genders.

Purpose: The Omicron subvariant BA.1 of SARS-CoV-2 was first detected in November 2021 and quickly spread worldwide, displacing the Delta variant. In this work, a characterization of the spread of this variant in Mexico is presented., Methods: The time to fixation of BA.1, the diversity of Delta sublineages, the population density, and the level of virus circulation during the inter-wave interval were determined to analyze differences in BA.1 spread., Results: BA.1 began spreading during the first week of December 2021 and became dominant in the next three weeks, causing the fourth COVID-19 epidemiological surge in Mexico. Unlike previous variants, BA.1 did not exhibit a geographically distinct circulation pattern. However, a regional difference in the speed of the replacement of the Delta variant was observed., Conclusions: Viral diversity and the relative abundance of the virus in a particular area around the time of the introduction of a new lineage seem to have influenced the spread dynamics, in addition to population density. Nonetheless, if there is a significant difference in the fitness of the variants, or if the time allowed for the competition is sufficiently long, it seems the fitter virus will eventually become dominant, as observed in the eventual dominance of the BA.1.x variant in Mexico.

Background: With the arrival of chikungunya (CHIKV) and zika (ZIKV) viruses in Mexico, there was a decrease in diagnosed dengue virus (DENV) cases. During the first years of cocirculation (2015-2017), the algorithms established by epidemiological surveillance systems and the installed capacity limited us to one diagnostic test per sample, so there was an underestimation of cases until September 2017, when a multiplex algorithm was implemented. Therefore, the objective of this study was determine the impact of the introduction of CHIKV and ZIKV on the incidence of diagnosed DENV in endemic areas of Mexico, when performing the rediagnosis, using the multiplex algorithm, in samples from the first three years of co-circulation of these arboviruses., Methodology and Principal Findings: For this, 1038 samples received by the Central Laboratory of Epidemiology between 2015 and 2017 were selected for this work. Viruses were identified by multiplex RT-qPCR, and the χ2 test was used to compare categorical variables. With the new multiplex algorithm, we identified 2.4 times the rate of arbovirosis as originally reported, evidencing an underestimation of the incidence of the three viruses. Even so, significantly less dengue was observed than in previous years. The high incidence rates of chikungunya and Zika coincided with periods of dengue decline. The endemic channel showed that the cases caused by DENV rose again after the circulation of CHIKV and ZIKV decreased. In addition, 23 cases of coinfection were identified, with combinations between all viruses., Conclusions and Significance: The results obtained in this study show for the first time the real impact on the detected incidence of dengue after the introduction of CHIKV and ZIKV in Mexico, the degree of underestimation of these arboviruses in the country, as well as the co-infections between these viruses, whose importance clinical and epidemiological are still unknown., Competing Interests: The authors have declared that no competing interests exist.

Objective: This study was to determine and compare the prevalences of polypharmacy and comorbidities in patients aged 50 years or older with those patients younger than 50 years in a Mexican population., Results: One hundred and twenty-five patients were enrolled, 60 (48%) were aged 50 years or older. The median CD4+ cell counts were 509 cells/μL (interquartile range [IQR]: 324-730) for the older patients and 384 cells/μL (IQR: 262-562) (P = 0.021) for the younger patients. Viral suppression were significantly higher in the older group: 80% vs. 63% (P = 0.037). The number of comorbidities was significantly higher in the older group, with a median of 2 (IQR: 2-3) vs. 1 (IQR: 0-1) (P ≤ 0.001). After adjustment of the logistic regression model in the older group, the following comorbidities differed between the age groups: systemic arterial hypertension (odds ratio [OR]: 15.75; 95% confidence interval [CI] 3.49-71.05; P = < 0.001), diabetes mellitus (OR: 14.36; 95% CI 1.79-115.07; P = 0.001), osteoarthritis (OR: 10.33; 95% CI 2.88-37.05; P = < 0.001), hyperlipidemia (OR: 2.78; 95% CI 1.22-6.34; P = 0.001), and polypharmacy (OR: 6.58; 95% CI 3.01-14.39; P = 0.001).

Background: The circulatory system is the main mechanism for transmission of the Hepatitis C Virus (HCV). A new class of HCV infections, Occult HCV infection (OCI), is defined as the presence of HCV-RNA in hepatocytes with the absence of HCV in the serum/plasma utilizing current laboratory assays. Different groups have reported the prevalence of OCI; however, its associated risk factors have not been established. In Mexico, there are no reports about OCI, so the objective of our study was to determine the prevalence of OCI in total blood donors in Mexico City, as well as its associated risk factors., Methods: Blood donors that were considered eligible for donation, according to NOM 253-SSA1-2012, were randomly selected. Demographic data was collected from 1,037 donors. Plasma and peripheral blood mononuclear cells were assessed for HCV-RNA. The presence of HCV-RNA was determined by nested PCR for the 5'-UTR region. Logistic regression was used to calculate the odds ratio (OR) and 95% confidence interval (95%CI) to determine the level of association., Results: The prevalence of OCI was 3.4% among blood donors. Homosexual relationships (OR = 5.52, 95%CI: 1.53-19.92, p<0.05) and acupuncture (OR = 3.56, 95%CI: 1.41-8.98, p<0.05) were significantly associated with OCI., Conclusion: There is a significant presence of OCI in the blood donor population in Mexico City. The main risk factors for OCI transmission are homosexual relationships and acupuncture. This study supports the increased use of sensitive and specific screening tests for blood bank testing., Competing Interests: The authors have declared that no competing interests exist.