How big of an impact do asymptomatic people have on the dynamics of an epidemic?

Asymptomatic carriers serve as a potential source of transmission of epidemic diseases. Exposed people who develop symptoms only get tested and remain isolated in their homes or sometimes in hospitals when needed. In contrast, the asymptomatic individuals go untested and spread the disease silently as they roam freely throughout their entire infectious lifetime. The work intends to explore the role of asymptomatic carriers in the transmission of epidemic diseases and investigate suitable optimal control strategies. We propose a SEIAQR compartmental model subdividing the total population into six different compartments. To illustrate the model's implication, we estimate the number of asymptomatic individuals using COVID-19 data during June 9–July 18, 2021 from Bangladesh. We then analyze the model to explore whether the epidemic subsides if the asymptomatic individuals are tested randomly and isolated. Finally, to gain a better understanding of the potential of this unidentified transmission route, we propose an optimal control model considering two different control strategies: personal protective measures and isolation of asymptomatic carriers through random testing. Our results show that simultaneous implementation of both control strategies can reduce the epidemic early. Most importantly, sustained effort in identifying and isolation of asymptotic individuals allows relaxation in personal protective measures. © 2023

Stationary distribution and probability density for a stochastic SEIR-type model of coronavirus (COVID-19) with asymptomatic carriers.

In this paper, we propose a stochastic SEIR-type model with asymptomatic carriers to describe the propagation mechanism of coronavirus (COVID-19) in the population. Firstly, we show that there exists a unique global positive solution of the stochastic system with any positive initial value. Then we adopt a stochastic Lyapunov function method to establish sufficient conditions for the existence and uniqueness of an ergodic stationary distribution of positive solutions to the stochastic model. Especially, under the same conditions as the existence of a stationary distribution, we obtain the specific form of the probability density around the quasi-endemic equilibrium of the stochastic system. Finally, numerical simulations are introduced to validate the theoretical findings.

The epidemiology and dynamics of COVID-19 disease transmission among healthcare workers of a tertiary healthcare setting in India.

Context: The novel coronavirus disease 2019 (COVID-19) that has emerged as a pandemic now has put health care workers (HCWs) at great risk as they are the warriors in frontlines screening and treating the infected patients. When a COVID-19-positive HCW is identified, its contacts need to be traced to check the spread of the infection among patients and other HCWs. Aims: This study was aimed to study epidemiology and risk factors associated with severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) infection among HCWs and to quantify the risk of infection among HCWs in a tertiary level health care setting. Settings and Design: This cross-sectional study enrolled all the HCWs who were exposed to a patient with COVID-19 in a tertiary level health care center, Rishikesh, Uttarakhand from 1st May to 30th July, 2020. Methods and Material: All the exposed HCWs were followed up for 14 days after the last exposure to a patient with confirmed COVID-19 infection. Epidemiological data were obtained using structured interviews. Statistical Analysis Used: The data were analyzed using SPSS 23.0. Frequencies and proportions were calculated for descriptive variables, and risk ratios were calculated for risk factors affecting the transmission of disease. Results: We observed that 1,141 HCWs of the tertiary level health care hospital were exposed to COVID-19 patients during the study period. A total of 22 HCWs were tested COVID-19 positive among these exposed HCWs. Univariate analysis revealed a high risk of exposure to be significantly associated with a higher secondary attack rate of SARS CoV-2. Conclusions: The study demonstrates the risk of COVID-19 transmission through asymptomatic carriers. Therefore, periodic testing of all health care workers is necessary to ensure early mitigation of the shortage of health care providers.

Clinical Characteristics of Immune Response in Asymptomatic Carriers and Symptomatic Patients With COVID-19.

The pandemic of coronavirus disease 2019 (COVID-19) has emerged as a major public health challenge worldwide. A comprehensive understanding of clinical characteristics and immune responses in asymptomatic carriers and symptomatic patients with COVID-19 is of great significance to the countermeasures of patients with COVID-19. Herein, we described the clinical information and laboratory findings of 43 individuals from Hunan Province, China, including 13 asymptomatic carriers and 10 symptomatic patients with COVID-19, as well as 20 healthy controls in the period from 25 January to 18 May 2020. The serum samples of these individuals were analyzed to measure the cytokine responses, receptor-binding domain (RBD), and nucleocapsid (N) protein-specific antibody titers, as well as SARS-CoV-2 neutralizing antibodies (nAbs). For cytokines, significantly higher Th1 cytokines including IL-2, IL-8, IL-12p70, IFN-γ, and TNF-α, as well as Th2 cytokines including IL-10 and IL-13 were observed in symptomatic patients compared with asymptomatic carriers. Compared with symptomatic patients, higher N-specific IgG4/IgG1 ratio and RBD-specific/N-specific IgG1 ratio were observed in asymptomatic carriers. Comparable nAbs were detected in both asymptomatic carriers and symptomatic patients with COVID-19. In the symptomatic group, nAbs in patients with underlying diseases were weaker than those of patients without underlying diseases. Our retrospective study will enrich and verify the clinical characteristics and serology diversities in asymptomatic carriers and symptomatic patients with COVID-19.

Nasopharyngeal Bacterial Microbiota Composition and SARS-CoV-2 IgG Antibody Maintenance in Asymptomatic/Paucisymptomatic Subjects.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes the coronavirus disease 2019 (COVID-19), ranging from asymptomatic conditions to severe/fatal lung injury and multi-organ failure. Growing evidence shows that the nasopharyngeal microbiota composition may predict the severity of respiratory infections and may play a role in the protection from viral entry and the regulation of the immune response to the infection. In the present study, we have characterized the nasopharyngeal bacterial microbiota (BNM) composition and have performed factor analysis in a group of 54 asymptomatic/paucisymptomatic subjects who tested positive for nasopharyngeal swab SARS-CoV-2 RNA and/or showed anti-RBD-IgG positive serology at the enrolment. We investigated whether BNM was associated with SARS-CoV-2 RNA positivity and serum anti-RBD-IgG antibody development/maintenance 20-28 weeks after the enrolment. Shannon's entropy α-diversity index [odds ratio (OR) = 5.75, p = 0.0107] and the BNM Factor1 (OR = 2.64, p = 0.0370) were positively associated with serum anti-RBD-IgG antibody maintenance. The present results suggest that BNM composition may influence the immunological memory against SARS-CoV-2 infections. To the best of our knowledge, this is the first study investigating the link between BNM and specific IgG antibody maintenance. Further studies are needed to unveil the mechanisms through which the BNM influences the adaptive immune response against viral infections.

Modes of Transmission of Novel Corona Virus (NCov)

BACKGROUND:- The global breakout in the new SARS-Coronavirus 2 have prompted many interrogations concerning this virus's origins & spread. The already stated information of the modes based on transferal also measuring the efficacy in regards to prophylactic estimates will support within limiting this COVID-19 upsurge. SARS-Coronavirus-2 transmission mechanisms have now been identified as respiratory droplets, physical contact and airborne. On the other hand researchers are looking into some of the other possible modes of transmission with some studies showing that the virus spreads through feces-oral, conjunctival secretion(eyes), sexual transmission, mother-to-fetal transmission, surface contact, saliva and asymptomatic carriers. The major goal of this review is to gain a better understanding of SARS-Coronavirus-2 transmission in addition to make exhortation for consist of along with avoiding the novel coronavirus. From its very beginning in Wuhan, China in December 2019, SARS CoV-2 has afflicted more than 31 million people worldwide, resulting in even more than 2 million fatalities. The world continues to be in the dark about a definite therapy for this extremely communicable diseases. Until then, we must depend on tried-and-true techniques to slow or prevent the spread of this viral disease, such as social withdrawal, hand cleanliness, and using a facial mask. OBJECTIVE:- The main goal of that kind of review article would be to focus on various methods of virus infection, comparisons of that kind of virus to similar past equivalency viral diseases including SARS and MERS, & multiple approaches which can be scheduled but are currently being implemented to minimize spread of contagious diseases in organizational citizenship, particularly in India. RESULTS:- According to an examination of many publications on route of transmission, the virus is very infectious and transmits by air droplets, frequent connection, and several conductive materials, and aerosol in the environment with high aerosol producing processes. It could also expand from both the uncomplicated and complicated phases, thus earlier detection is critical. This also mutates in diverse host conditions, thus various strains must be used in vaccine manufacturing. CONCLUSIONS:- Advance identification, social distance, quarantine or positive patients, and pulmonary hygiene are the major weaponry now known to cope with this virus until a suitable therapy or vaccination becomes available very soon, according to the findings. © The Electrochemical Society

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) viral positivity and their burden in saliva of asymptomatic carriers - a systematic review and meta-analysis.

AIMS: The coronavirus disease 2019 (COVID-19) due to the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) can present either as an asymptomatic carrier state or an acute respiratory disease, with or without severe pneumonia. The asymptomatic carriers are a challenge for the dental profession as the infection could be transmitted via virus-laden, and saliva in dental settings through aerosol-generating procedures (AGPSs). The aim of this review was to perform a systematic review of SARS-CoV-2 in the saliva of asymptomatic individuals. MATERIALS AND METHODS: PubMed, Google scholar, and MedRxiv databases were searched between and a systematic review and meta-analysis of the available data were performed to assess the viral burden in the saliva of asymptomatic carriers of SARS-CoV-2. All investigators of the included studies used qRT-PCR to detect SARS-CoV-2 and yield quantitative data (the Ct values) appertaining to the viral load. RESULTS: A total of 322 records in the English literature were identified, and eight studies with 2642 SARS-CoV-2-positive and asymptomatic individuals were included in the final analysis. Of these, 16.7% (95% CI: 11-23%) yielded SARS-CoV-2-positive saliva samples in comparison to 13.1% (95% CI: 12-17%) of the respiratory specimens (nasopharyngeal or nose-throat swabs). CONCLUSION: As approximately 1 in 5 to 1 in 10 asymptomatic individuals harbour SARS-CoV-2 in either saliva or respiratory secretions, our results highlight the need for continued vigilance and the critical importance of maintaining strict, additional infection control regimens for the foreseeable future to mitigate the potential risks of COVID-19 transmission in dentistry.

Clinical characteristics and infectivity of asymptomatic carriers of SARS-CoV-2 (Review).

Since December 2019, the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a global pandemic. At present, confirmed patients are the main source of infection, while a number of studies have indicated that asymptomatic carriers also have the ability to spread the virus. As of September 29, 2020, as the first country to report coronavirus disease 2019 (COVID-19), China has 375 asymptomatic infections according to the National Health Commission of China. Asymptomatic carriers have become the current focus of global epidemic prevention and control efforts. The present review article provides a brief introduction on the clinical characteristics and infectivity of asymptomatic carriers, and makes suggestions for the identification of asymptomatic carriers.

Epidemiological feature, viral shedding, and antibody seroconversion among asymptomatic SARS-CoV-2 carriers and symptomatic/presymptomatic COVID-19 patients.

BACKGROUND: Novel coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is pandemic. However, data concerning the epidemiological features, viral shedding, and antibody dynamics between asymptomatic SARS-CoV-2 carriers and COVID-19 patients remain controversial. METHODS: We enrolled 193 SARS-CoV-2 infected subjects in Ningbo and Zhoushan, Zhejiang, China, from January 21 to March 6, 2020. All subjects were followed up to monitor the dynamics of serum antibody immunoglobulin M (IgM) and IgG against SARS-CoV-2 using colloidal gold-labeled and enzyme-linked immunosorbent assays. RESULTS: Of those, 31 were asymptomatic SARS-CoV-2 carriers, 148 symptomatic COVID-19 patients, and 14 presymptomatic COVID-19 patients. Compared to symptomatic COVID-19 patients, asymptomatic carriers were younger and had higher levels of white blood cell and lymphocyte, lower level of C-reactive protein, and shorter viral shedding duration. Conversion of IgM from positive to negative was shorter in asymptomatic carriers than in COVID-19 patients (7.5 vs. 25.5 days, P = 0.030). The proportion of those persistently seropositive for IgG against SARS-CoV-2 was higher in COVID-19 patients than in asymptomatic carriers (66.1% vs. 33.3%, P = 0.037). Viral load was higher in symptomatic patients than presymptomatic patients (P = 0.003) and asymptomatic carriers (P = 0.004). Viral shedding duration was longer in presymptomatic COVID-19 patients than in asymptomatic carriers (48.0 vs. 24.0 days, P = 0.002). Asymptomatic carriers acquired infection more from intra-familial transmission than did COVID-19 patients (89.0% vs. 61.0%, P = 0.028). In 4 familial clusters of SARS-CoV-2 infection, asymptomatic carriers were mainly children and young adults while severe COVID-19 was mainly found in family members older than 60 years with comorbidities. CONCLUSION: Asymptomatic carriers might have a higher antiviral immunity to clear SARS-CoV-2 than symptomatic COVID-19 patients and this antiviral immunity should be contributable to innate and adaptive cellular immunity rather than humoral immunity. The severity of COVID-19 is associated with older age and comorbidities in familial clustering cases.

Reviewing the Ethical Concerns of the Convalescent Plasma Therapy in COVID-19.

The understanding of coronavirus disease 2019 (COVID-19) is evolving periodically. There is also a marked increase in COVID-19 patients' demand for the provision of COVID-19 convalescent plasma (CCP) therapy. With the review of the literature, the stage of speculation is quickly moving towards conformity, with the interim guidelines given by the Food and Drug Administration (FDA) in the United States, United Kingdom's blood transfusion services, Saudi's FDA, and the Indian Council for Medical Research, in addition to the European health authorities. It is prudent to address the ethical concerns that merit consideration while harvesting and utilizing CCP as a therapeutic tool in local hospital setting.

SARS-CoV-2 universal screening upon adult hospital admission in Southern Israel.

As the prevalence of coronavirus disease 2019 (COVID-19) increased in the local community, severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) universal screening was initiated for all adult patients admitted through the emergency departments (EDs) at Soroka University Medical Centre. Of 8518 patients screened, 288 (3.38%) tested positive. One hundred and thirty-three (46%) positive cases were asymptomatic and would have been admitted without necessary precautions. Patients with symptoms that may be attributable to COVID-19 were significantly older and were admitted through the medical ED. Patients of Bedouin Arab ethnicity accounted for half of those who tested positive, which was double their prevalence in the general population. These findings indicate that universal SARS-CoV-2 screening on adult hospital admission is crucial in areas with a high prevalence of COVID-19.

Analysis of current SARS-CoV-2 infection in a large population of blood donors evidenced that RNAemia is rare in plasma.

BACKGROUND: Transmission of SARS-CoV-2 by asymptomatic individuals and by blood transfusion are important issues to understand to control the viral spread. In this work, we estimated the current SARS-CoV-2 infection rate in blood donors from Belo Horizonte, Brazil. STUDY DESIGN AND METHODS: Saliva and blood samples were collected from 4103 blood donors from June 15 to September 30, 2020. Saliva samples were tested by real-time RT-PCR for SARS-CoV-2 in mini-pools of four samples. Individual samples were tested for positive or inconclusive pools, and positive donors had their plasma tested. RESULTS: Twenty-seven (0.66%) blood donors were positive for SARS-CoV-2 in their saliva, but their plasma was negative, except for one, who presented a high viral load in saliva and nasopharyngeal samples and RNAemia in the plasma close to the limit of detection. Fourteen (56%) positive blood donors reported mild symptoms related to COVID-19 after donation, but the viral load levels were not statistically different between symptomatic and asymptomatic individuals. DISCUSSION: Despite the measures taken by Blood Centers to avoid blood donors with SARS-CoV-2 infection, asymptomatic or presymptomatic carriers are able to donate. The risk of the virus transmission by transfusion seems to be negligible since plasma RNAemia was seen at a very low level in only one (3.7%) of the positive donors, but other studies must be performed to confirm this finding.

Severe Acute Respiratory Syndrome Coronavirus 2 Viral RNA Load Status and Antibody Distribution Among Patients and Asymptomatic Carriers in Central China.

This study aimed to monitor severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral loads and specific serum-antibodies (immunoglobulin [Ig] G and M) among confirmed patients and asymptomatic carriers from returning healthy travelers. The throat swabs, sputum, and stool samples from 57 hospitalized coronavirus disease (COVID-19) patients and 8 asymptomatic carriers, among 170 returning healthy travelers were tested using reverse-transcription real-time polymerase chain reaction. SARS-CoV-2 IgM/IgG antibodies were detected via serum chemiluminescence assay. Sequential results showed higher viral RNA loads in the throat, sputum, and stool samples at 3-12 and 6-21 days after symptom onset among severely ill COVID-19 patients. Shorter viral habitation time (1-8 days) was observed in the oropharyngeal site and intestinal tract of asymptomatic carriers. The IgG and IgM response rates were 19/37 (51.4%) and 23/37 (62.6%) among the 29 confirmed patients and 8 asymptomatic carriers, respectively, within 66 days from symptom or detection onset. The median duration between symptom onset and positive IgG and IgM results was 30 (n=23; interquartile range [IQR]=20-66) and 23 (n=19; IQR=12-28) days, respectively. Of 170 returning healthy-travelers to China, 4.7% were asymptomatic carriers (8/170) within 2 weeks, and the IgG and IgM positivity rate was 12.8% (12/94). IgM/IgG-positivity confirmed 3 suspected SARS-CoV-2 cases, despite negative results for SARS-CoV-2 RNA. Compared with other respiratory viral infectious diseases, COVID-19 has fewer asymptomatic carriers, lower antibody response rates, and a longer antibody production duration in recovered patients and the contacted healthy population. This is an indication of the complexity of COVID-19 transmission.

Estimated prevalence and viral transmissibility in subjects with asymptomatic SARS-CoV-2 infections in Wuhan, China.

The role of subjects with asymptomatic SARS-CoV-2 infection in the current pandemic is not well-defined. Based on two different approaches to estimate the culminative attack rate (seroprevalence of antibodies against SARS-CoV-2, and a four compartment mathematical model) and the reported number of patients with COVID-19, the ratio of asymptomatic versus symptomatic SARS-CoV-2 infection was estimated to be 7 (95% CI: 2.8-12.4) in Wuhan, Hubei, China, the first epicenter of this pandemic, which has settled with no new cases. Together with detailed recording of the contact sources in a cohort of patients, and applying the estimations to an established mathematical model, the viral transmissibility of the subjects with asymptomatic SARS-CoV-2 infection is around 10% of that of the symptomatic patients (95% CI: 7.6%-12.3%). Public health measures/policies should address this important pool of infectious source in combat against this viral pandemic.

Systematic screening on admission for SARS-CoV-2 to detect asymptomatic infections.

The proportion of asymptomatic carriers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) remains elusive and the potential benefit of systematic screening during the SARS-CoV-2-pandemic is controversial. We investigated the proportion of asymptomatic inpatients who were identified by systematic screening for SARS-CoV-2 upon hospital admission. Our analysis revealed that systematic screening of asymptomatic inpatients detects a low total number of SARS-CoV-2 infections (0.1%), questioning the cost-benefit ratio of this intervention. Even when the population-wide prevalence was low, the proportion of asymptomatic carriers remained stable, supporting the need for universal infection prevention and control strategies to avoid onward transmission by undetected SARS-CoV-2-carriers during the pandemic.

Asymptomatic SARS COV-2 carriers among nursing home staff: A source of contamination for residents?

OBJECTIVES: To show that circulation of SARS-COV-2 in nursing homes in France can come from staff as well as residents' families, whether they are known or not to have had COVID-19. METHODS: This study reports a screening campaign of asymptomatic staff working in elderly nursing homes in Paris where the virus had been circulating actively in March and April 2020. RESULTS: Before the screening campaign, the rate of symptomatic COVID-19 was 23.3% among the residents and 12.1% among their home employees. Within a 72 h screening period, all employees not known to have the virus were screened by RT-PCR in nasopharyngeal swabs. Among the 241 screened employees, 32 (13.3%) tested positive for SARS-CoV-2 on RT-PCR. SARS-CoV-2 carriers and non-carriers did not differ in term of gender, age or type of staff. Staff carrying SARS-CoV-2 were strictly asymptomatic in 75% of cases while during the days following or before the test, 25% presented mild symptoms of COVID-19. Considering both symptomatic and asymptomatic cases, 66 out of 281 (23.5%) of the home employees had been carriers for COVID-19. CONCLUSION: Screening for viral carriage of asymptomatic staff in nursing homes can avoid contact and transmission to frequently severely vulnerable residents.

[Laboratory testing, prevention and control of asymptomatic carriers of coronavirus disease 2019].

With many hard efforts, the epidemic prevention and control work in China has borne successful, accelerating the gradual restoration of production, living order and routine medical work. However, there is increasing evidence that many patients with COVID-19 are asymptomatic, but they are potential transmitter of the virus. There are difficulties in screening for asymptomatic infections, which makes it more difficult for national prevention and control of this epidemic. Therefore, it is urgent to develop better screening and laboratory testing for asymptomatic infections with COVID-19 with high speed, sensitivity and specificity. It is also important to improve our risk assessment, prevention and control strategies to further prevent the spread of the epidemic.

Clinical characteristics of asymptomatic carriers of novel coronavirus disease 2019: A multi-center study in Jiangsu Province.

Asymptomatic SARS-CoV-2-infected individuals are thought to play major roles in virus transmission. This study aimed to analyze the characteristics of asymptomatic carriers with COVID-19 to control the spread of the virus. We retrospectively investigated the clinical characteristics of 648 consecutive subjects who were enrolled in the study and were divided into asymptomatic carriers, mild cases, ordinary cases, severe or critical cases, and evaluated their impact on disease severity by means of Spearman correlation and multiple regression analyses. Receiver operating characteristic curve analysis was conducted to determine the optimum cutoff levels of laboratory findings for diagnostic predictors of asymptomatic carriers of COVID-19. In our study, a total of 648 subjects on admission with a mean age of 45.61 y including 345 males and 303 females were enrolled in our study. The leukocyte, lymphocyte, eosinophil, platelet, C-reactive protein, interleukin-6, CD3+, CD4+, and CD8 + T lymphocyte levels, and the erythrocyte sedimentation rate differed significantly among the groups (all p ≤ 0.05). Disease severity was negatively associated with the CD3+ (r = -0.340; p < 0.001), CD4+ (r = -0.290; p = 0.001) and CD8+ (r = -0.322; p < 0.001) T lymphocyte levels. The significant diagnostic predictors of asymptomatic carriers of COVID-19 included the blood cell, cytokine, and T lymphocyte subset levels. Inflammation and immune response may play important roles in disease progression. Hence, the laboratory parameters identified should be considered in clinical practice, which provide new insights into the identification of asymptomatic individuals and the prevention of virus transmission.