Quantification of asymptomatic infections is fundamental for effective public health responses to the COVID-19 pandemic. Discrepancies regarding the extent of asymptomaticity have arisen from inconsistent terminology as well as conflation of index and secondary cases which biases toward lower asymptomaticity. We searched PubMed, Embase, Web of Science, and World Health Organization Global Research Database on COVID-19 between January 1, 2020 and April 2, 2021 to identify studies that reported silent infections at the time of testing, whether presymptomatic or asymptomatic. Index cases were removed to minimize representational bias that would result in overestimation of symptomaticity. By analyzing over 350 studies, we estimate that the percentage of infections that never developed clinical symptoms, and thus were truly asymptomatic, was 35.1% (95% CI: 30.7 to 39.9%). At the time of testing, 42.8% (95% prediction interval: 5.2 to 91.1%) of cases exhibited no symptoms, a group comprising both asymptomatic and presymptomatic infections. Asymptomaticity was significantly lower among the elderly, at 19.7% (95% CI: 12.7 to 29.4%) compared with children at 46.7% (95% CI: 32.0 to 62.0%). We also found that cases with comorbidities had significantly lower asymptomaticity compared to cases with no underlying medical conditions. Without proactive policies to detect asymptomatic infections, such as rapid contact tracing, prolonged efforts for pandemic control may be needed even in the presence of vaccination.

https://www.pnas.org/content/pnas/118/34/e2109229118.full.pdf

Asymptomatic SARS-CoV-2 infection: A systematic review and meta-analysis.

Corona Virus Disease 2019 (COVID-19) caused by the novel coronavirus, results in an acute respiratory condition coronavirus 2 (SARS-CoV-2) and is highly infectious. The recent spread of this virus has caused a global pandemic. Currently, the transmission routes of SARS-CoV-2 are being established, especially the role of environmental transmission. Here we review the environmental transmission routes and persistence of SARS-CoV-2. Recent studies have established that the transmission of this virus can occur, amongst others, in the air, water, soil, cold-chain, biota, and surface contact. It has also been found that the survival potential of the SARS-CoV-2 virus is dependent on different environmental conditions and pollution. Potentially important pathways include aerosol and fecal matter. Particulate matter may also be a carrier for SARS-CoV-2. Since microscopic particles can be easily absorbed by humans, more attention must be focused on the dissemination of these particles. These considerations are required to evolve a theoretical platform for epidemic control and to minimize the global threat from future epidemics.

The role of airborne particles and environmental considerations in the transmission of SARS-CoV-2

The current SARS-CoV-2 pandemic is a historical event that has come to change the way of life for humanity; where the population is the main subject of cause and solution. Considering the global variation of propagation, each country has taken different positions, decisions and resources where the time for making different decisions has also been an important factor. In Mexico, the SARS CoV-2 situation has been confronted mainly with government decisions and the actions of the population. The successes or failures have impacted various dimensions of society in each of the states that make up the country. In this research, some impacted life dimensions are analyzed: Social, mental, educational, economic and environmental. It is possible to say that the impact of the pandemic were influenced, among other aspects; by the state of health and nutrition associated with the lifestyle in which the population was at the arrival of the pandemic. This impact is also influenced by commercial activities, which are linked to the economic mobility of those who buy and those who sell. Also, other aspects that have influenced the impact of this pandemic; it is possible to highlight the lack of culture on the part of the population in the use of face masks and the non-obligatory use of it by the leaders. This, added to various other factors, have had a great impact on the number of infected cases and deaths in the country; primarily in Mexico City and the State of Mexico. It is worth mentioning that, despite the negative impact due to the pandemic, there are also positive aspects. Finally, it is possible to say that it is necessary for the population to develop more awareness. The population has a definitive role in containing the pandemic and to incorporate the new changes, in its life in order to precisely preserve.

https://www.atlas-tjes.org/index.php/tjes/article/download/171/155

Impact of COVID-19 in Mexico: A vision

Background and Objectives: Sentinel surveillance in the early stage of the COVID-19 pandemic in Mexico represented a significant cost reduction and was useful in estimating the population infected with SARS-CoV-2 However, it also implied that many patients were not screened and therefore had no accurate diagnosis In this study, we carried out a population-based SARS-CoV-2 screening in Mexico to evaluate the COVID-19-related symptoms and their weighting in predicting SARS-CoV-2 infection We also discuss this data in the context of the operational definition of suspected cases of COVID-19 established by the Mexican Health Authority’s consensus Materials and Methods: One thousand two hundred seventy-nine subjects were included They were screened for SARS-CoV-2 using RT-PCR The weighting of COVID-19 symptoms in predicting SARS-CoV-2 infection was evaluated statistically Results: Three hundred and twenty-five patients were positive for SARS-CoV-2 and 954 were negative Fever, asthenia, dysgeusia, and oxygen saturation predicted SARS-CoV-2 infection (odds ratios ranged from 174 to 498; p < 005) The percentage of asymptomatic COVID-19 patients was 36% and only 3815% met the Mexican operational definition Cq-values for the gene N of SARS-CoV-2 were significantly higher in asymptomatic subjects than in the groups of COVID-19 patients with neurological, respiratory, and/or musculoskeletal manifestations (p < 005) Conclusions: Dysgeusia, fever, and asthenia increased the odds of a positive result for COVID-19 174–498-fold among the study population Patients with neurological, respiratory, and/or musculoskeletal manifestations had higher viral loads at COVID-19 diagnosis than those observed in asymptomatic patients A high percentage of the participants in the study (6185%) did not meet the operational definition for a suspected case of COVID-19 established by the Mexican Health Authority’s consensus, representing a high percentage of the population that could have remained without a COVID-19 diagnosis, so becoming a potential source of virus spread

https://www.mdpi.com/1648-9144/57/4/363/pdf

Population-Based COVID-19 Screening in Mexico: Assessment of Symptoms and Their Weighting in Predicting SARS-CoV-2 Infection.

The methods to ascertain cases of an emerging infectious disease are typically biased toward cases with more severe disease, which can bias the average infection-severity profile. Here, we conducted a systematic review to extract information on disease severity among index cases and secondary cases identified by contact tracing of index cases for COVID-19. We identified 38 studies to extract information on measures of clinical severity. The proportion of index cases with fever was 43% higher than for secondary cases. The proportion of symptomatic, hospitalized, and fatal illnesses among index cases were 12%, 126%, and 179% higher than for secondary cases, respectively. We developed a statistical model to utilize the severity difference, and estimate 55% of index cases were missed in Wuhan, China. Information on disease severity in secondary cases should be less susceptible to ascertainment bias and could inform estimates of disease severity and the proportion of missed index cases.

Andres Morales-Esquivel

Papers

The role of close contacts of COVID-19 patients in the SARS-CoV-2 transmission: an emphasis on the percentage of nonevaluated positivity in Mexico.