Comparative epidemiology of five waves of COVID-19 in Mexico, March 2020-August 2022.

BACKGROUND: The Mexican Institute of Social Security (IMSS) is the largest health care provider in Mexico, covering about 48% of the Mexican population. In this report, we describe the epidemiological patterns related to confirmed cases, hospitalizations, intubations, and in-hospital mortality due to COVID-19 and associated factors, during five epidemic waves recorded in the IMSS surveillance system. METHODS: We analyzed COVID-19 laboratory-confirmed cases from the Online Epidemiological Surveillance System (SINOLAVE) from March 29th, 2020, to August 27th, 2022. We constructed weekly epidemic curves describing temporal patterns of confirmed cases and hospitalizations by age, gender, and wave. We also estimated hospitalization, intubation, and hospital case fatality rates. The mean days of in-hospital stay and hospital admission delay were calculated across five pandemic waves. Logistic regression models were employed to assess the association between demographic factors, comorbidities, wave, and vaccination and the risk of severe disease and in-hospital death. RESULTS: A total of 3,396,375 laboratory-confirmed COVID-19 cases were recorded across the five waves. The introduction of rapid antigen testing at the end of 2020 increased detection and modified epidemiological estimates. Overall, 11% (95% CI 10.9, 11.1) of confirmed cases were hospitalized, 20.6% (95% CI 20.5, 20.7) of the hospitalized cases were intubated, and the hospital case fatality rate was 45.1% (95% CI 44.9, 45.3). The mean in-hospital stay was 9.11 days, and patients were admitted on average 5.07 days after symptoms onset. The most recent waves dominated by the Omicron variant had the highest incidence. Hospitalization, intubation, and mean hospitalization days decreased during subsequent waves. The in-hospital case fatality rate fluctuated across waves, reaching its highest value during the second wave in winter 2020. A notable decrease in hospitalization was observed primarily among individuals ≥ 60 years. The risk of severe disease and death was positively associated with comorbidities, age, and male gender; and declined with later waves and vaccination status. CONCLUSION: During the five pandemic waves, we observed an increase in the number of cases and a reduction in severity metrics. During the first three waves, the high in-hospital fatality rate was associated with hospitalization practices for critical patients with comorbidities.

Infection and death by COVID-19 in a cohort of healthcare workers in Mexico.

OBJECTIVE: This study aimed to estimate the risk of SARS-Cov2 infection and severe COVID-19 among healthcare workers from a major social security system. METHODS: This study actively followed a cohort of social security workers from March to December 2020 to determine the number of laboratory-confirmed symptomatic cases, asymptomatic associated contacts and COVID-19-associated hospitalizations and deaths. Workers were classified into those providing direct care to infected patients (COVID teams), other active healthcare workers (OAHCW), and workers under home protection (HPW). The number of cases and rates were also estimated by job category. RESULTS: Among a total of 542 381 workers, 41 461 were granted stay-at-home protection due to advanced age or comorbidities. Among the 500 920 total active workers, 85 477 and 283 884 were classified into COVID teams and OAHCW, respectively. Infection rates for COVID teams, OAHCW, and HPW were 20.1% [95% confidence interval (CI) 19.8-20.4], 13.7% (95% CI 15.0-15.3), and 12.2% (95% CI 11.8-12.5), respectively. The risk of hospitalization was higher among HPW. COVID teams had lower mortality rate per 10 000 workers compared to HPW (5.0, 95% CI 4.0-7.0 versus 18.1, 95% CI 14.0-23.0). Compared to administrative workers, ambulance personnel (RR 1.20; 95% CI 1.09-1.32), social workers (RR 1.16; 95% CI 1.08-1.24), patient transporters (RR 1.15; 95% CI 1.09-1.22) and nurses (RR 1.13; 95% CI 1.10-1.15) had a higher risk of infection after adjusting for age and gender. Crude differences in mortality rates were observed according to job category, which could be explained by differences in age, sex, and comorbidity distribution. Diabetes, obesity, hypertension, hemolytic anemia, and HIV were associated with increased fatality rates. CONCLUSIONS: COVID team workers had higher infection rates compared to the total population of active workers and HPW. Doctors had lower risk of infection than respiratory therapists, nurses, and patient transporters, among whom interventions should be reconsidered to reduce risks. The presence of comorbidities, such as diabetes, obesity, arterial hypertension, hemolytic anemia, and HIV, increased the likelihood of complications caused by COVID-19, culminating in a poor prognosis.

SARS-CoV-2 IgG Antibodies Seroprevalence and Sera Neutralizing Activity in MEXICO: A National Cross-Sectional Study during 2020.

Until recently, the incidence of COVID-19 was primarily estimated using molecular diagnostic methods. However, the number of cases is vastly underreported using these methods. Seroprevalence studies estimate cumulative infection incidences and allow monitoring of transmission dynamics, and the presence of neutralizing antibodies in the population. In February 2020, the Mexican Social Security Institute began conducting anonymous unrelated sampling of residual sera from specimens across the country, excluding patients with fever within the previous two weeks and/or patients with an acute respiratory infection. Sampling was carried out weekly and began 17 days before Mexico's first officially confirmed case. The 24,273 sera obtained were analyzed by chemiluminescent-linked immunosorbent assay (CLIA) IgG S1/S2 and, later, positive cases using this technique were also analyzed to determine the rate of neutralization using the enzyme-linked immunosorbent assay (ELISA). We identified 40 CLIA IgG positive cases before the first official report of SARS-CoV-2 infection in Mexico. The national seroprevalence was 3.5% in February and 33.5% in December. Neutralizing activity among IgG positives patients during overall study period was 86.1%. The extent of the SARS-CoV-2 infection in Mexico is 21 times higher than that reported by molecular techniques. Although the general population is still far from achieving herd immunity, epidemiological indicators should be re-estimated based on serological studies of this type.

Hypertension, Diabetes and Obesity, Major Risk Factors for Death in Patients with COVID-19 in Mexico.

BACKGROUND: Mexico has reported high death and case fatality rates due to COVID-19. Several comorbidities have been related to mortality in COVID-19, as hypertension, diabetes, coronary heart disease, chronic obstructive lung disease and chronic kidney disease. AIMS: To describe the main clinical characteristics of COVID-19 in the major social security institution in Mexico, as well as the contribution of chronic comorbidities and the population attributable fraction related to them. METHODS: Data for all patients with a positive test for SARS-CoV-2 in the institutional database was included for analysis. Demographic information, the presence of pneumonia and whether the patient was hospitalized or treated at home as an outpatient as well as comorbidities were analyzed. Case fatality rate was estimated for different groups. Odds ratios with 95% confidence intervals from a logistic regression model were estimated, as well as the population attributable fraction. RESULTS: By November 13, 2020, 323,671 subjects with COVID-19 infection have been identified. Case fatality rate is higher in males (20.2%), than in females (13.0%), and increases with age. Case fatality rate increased with the presence of obesity, hypertension and/or diabetes. Age and sex were major independent risk factors for mortality, as well as the presence of pneumonia, diabetes, hypertension, obesity, immunosuppression, and end-stage kidney disease. The population attributable fraction due to obesity in outpatients was 16.8%. CONCLUSIONS: Major cardiovascular risk factors and other comorbidities increase the risk of dying in patients with COVID-19. Identification of populations with high fatality in COVID-19, provides insight to deal with this pandemic by health services in Mexico.

Genomic Analysis of Early SARS-CoV-2 Variants Introduced in Mexico.

The coronavirus disease 2019 (COVID-19) pandemic has affected most countries in the world. Studying the evolution and transmission patterns in different countries is crucial to enabling implementation of effective strategies for disease control and prevention. In this work, we present the full genome sequence for 17 SARS-CoV-2 isolates corresponding to the earliest sampled cases in Mexico. Global and local phylogenomics, coupled with mutational analysis, consistently revealed that these viral sequences are distributed within 2 known lineages, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) lineage A/G, containing mostly sequences from North America, and lineage B/S, containing mainly sequences from Europe. Based on the exposure history of the cases and on the phylogenomic analysis, we characterized 14 independent introduction events. Additionally, three cases with no travel history were identified. We found evidence that two of these cases represented local transmission cases occurring in Mexico during mid-March 2020, denoting the earliest events described for the country. Within this local transmission cluster, we also identified an H49Y amino acid change in the Spike protein. This mutation represents a homoplasy occurring independently through time and space and may function as a molecular marker to follow any further spread of these viral variants throughout the country. Our results provide a general picture of the SARS-CoV-2 variants introduced at the beginning of the outbreak in Mexico, setting the foundation for future surveillance efforts.IMPORTANCE Understanding the introduction, spread, and establishment of SARS-CoV-2 within distinct human populations as well as the evolution of the pandemics is crucial to implement effective control strategies. In this work, we report that the initial virus strains introduced in Mexico came from Europe and the United States and that the virus was circulating locally in the country as early as mid-March. We also found evidence for early local transmission of strains with a H49Y mutation in the Spike protein, which could be further used as a molecular marker to follow viral spread within the country and the region.