ABSTRACT
Background: Vertical transmission of SARS-CoV-2 has been reported but appears uncommon. Objectives This study systematically reviewed the evidence on vertical transmission of SARS-CoV-2 from pregnant women to their neonates. Search strategy Literature searches in WHO Covid-19 Database, LitCovid, medRxiv, and Google Scholar for SARS-CoV-2 using keywords and associated synonyms, search date to 20 December 2020; no language restrictions. Selection criteria Studies of any design reporting transmission. Data collection and analysis Two reviewers independently assessed article eligibility and extracted data. Results were reported descriptively; no meta-analyses were possible. Main results 106 studies were included: 40 reviews and 66 primary studies, most conducted in hospitals. 32 case reports were assessed as high risk of bias, due to the study design; across the 34 remaining primary studies, risk of bias was low to moderate. Sixteen case reports described vertical transmission. In cohort studies and case series, 65/2391 (2.7%) neonates born to mothers with a COVID-19 diagnosis tested positive for SARS-CoV-2 within 24 hours of birth; the proportion of positive neonates ranged from 0% to 22%. Twenty studies reported no vertical transmission. Maternal symptomatology and mode of delivery were not correlated with vertical transmission. 7/25 studies of placental tissue identified SARS-CoV-2; vertical transmission was infrequent. No study reported the results of viral culture to detect SARS-CoV-2. Conclusions These findings indicate that vertical transmission is possible, but not frequent. Further high-quality studies are needed to understand vertical transmission. Funding World Health Organization: WHO registration No 2020/1077093.
Subject(s)
COVID-19ABSTRACT
Background Organ transplant recipients are at increased vulnerability to SARS-CoV-2 due to immunosuppression and may pose a continued transmission risk especially within hospital settings. Detailed case reports including symptoms, viral load and infectiousness, defined by the presence of replication-competent viruses in culture, provide an opportunity to examine the relationship between clinical course, burden and contagiousness, and provide guidance on release from isolation. Objectives We performed a systematic review to investigate the relationship in transplant recipients between serial SARS-CoV-2 RT-PCR cycle threshold (Ct) value or cycle of quantification value (Cq), or other measures of viral burden and the likelihood and duration of the presence of infectious virus based on viral culture including the influence of age, sex, underlying pathologies, degree of immunosuppression, and/or vaccination on this relationship. Methods We searched LitCovid, medRxiv, Google Scholar and WHO Covid-19 databases, from 1 November 2019 until 31 December 2021. We included studies reporting relevant data for transplantees with SARS-CoV-2 infection: results from serial RT-PCR testing and viral culture data from the same respiratory samples. We assessed methodological quality using five criteria, and synthesised the data narratively and graphically. Results We included 10 case reports and case series reporting on 38 transplantees. We observed a relationship between proxies of viral burden and likelihood of shedding replication-competent SARS-CoV-2. Two individuals shed replication-competent viruses over 100 days after infection onset. Lack of standardisation of testing and reporting platforms precludes establishing a definitive viral burden cut-off. However, most transplantees stopped shedding competent viruses when the RT-PCR cycle threshold was above 30 despite differences across platforms. Conclusions Viral burden is a reasonable proxy for infectivity when considered within the context of the clinical status of each patient. Standardised study design and reporting are essential to standardise guidance based on an increasing evidence base.
Subject(s)
COVID-19ABSTRACT
This is a protocol for a systematic review that aims to evaluate the role of viral cultures for assessing airborne transmission of SARS-CoV-2. The review will address the following research questions: Are airborne samples infectious? If so, what proportion are infectious, and what is the distance and duration of infectiousness in the air? What is the relationship between infectiousness and airborne PCR cycle threshold (Ct)? Is there evidence of a chain of transmission that establishes an actual instance of airborne transmission of SARS-CoV-2? What circumstances might facilitate infectious viruses being airborne over long distances? We will search LitCovid, medRxiv, Google Scholar, and the WHO Covid-19 database to identify relevant studies. We will include studies reporting airborne transmission attempting viral culture or serial qRT-PCR with or without genomic sequencing. Predictive or modelling studies will be excluded. We will assess the quality of included studies using previously published criteria.
Subject(s)
COVID-19ABSTRACT
Background The transmission role of SARS-Cov-2 infected persons who develop symptoms post testing (pre symptomatics) or not at all throughout the course of positivity (asymptomatics) is unknown. We carried out a systematic review of available evidence to determine whether they were infectious or not and if so for how long and their probable contribution to the pandemic spread of SARS-CoV-2. Methods We searched LitCovid, medRxiv, Google Scholar and the WHO Covid-19 databases and reference lists of included studies. Search terms were COVID-19, SARS-CoV-2, transmission, asymptomatic, presymptomatic and appropriate synonyms. Searches were carried out to 31 March 2021. We included studies on people exposed to SARS CoV-2 within 2-14 days (incubation time) of close contact or suspected community or institutional exposure to index asymptomatic (at the time of observation) infected individuals, as defined in the study. We included studies with a proven or hypothesised chain of transmission with secondary case infected based on fulfilling a confirmed or probable case definition and confirmation of infectiousness and transmission outcome based either on serial PCR cycle threshold readings or viral culture or gene sequencing or any combination thereof and adequate follow up. We assessed the reliability of symptom and sign survey compatible with contemporary knowledge and extracted documentation of the likelihood of transmission, presence of replicating virus and/or documentation of phylodynamics (genetic sequence lineage) and/or adequate follow-up and reporting of symptoms and signs. We wrote to all included studies corresponding authors to request further details and assessed likelihood of transmission using adapted causality criteria. Results We included 18 studies from a variety of settings. Because of the current lack of standardized methodology and clear reporting criteria there was substantial methodological variation in transmission studies. Asymptomatic prevalence at the time of initial testing varied from 12.5% to 100% and of these 6% to 100% were pre-symptomatic cases, depending on the setting and the methods of case ascertainment and the population. Nursing/care home facilities reported high rates of presymptomatic: 50% - 100% (n=3 studies). Fifteen studies were classified as high risk and three studies at moderate risk of symptom ascertainment bias. In practice, this assessment means that high-risk studies may be less likely to distinguish between pre-symptomatic and asymptomatic cases. Six of the asymptomatic studies and four presymptomatic studies reported growing infectious virus although the data was too sparse to determine duration of infectiousness. Three studies were judged as providing possible and three of probable/likely evidence of asymptomatic transmission of SARs-CoV-2. Five studies provided evidence of possible and two of probable/likely presymptomatic transmission of SARs-CoV-2. Author response rate was 100%. Conclusions Reliable studies included here provide probable evidence of transmission of SARS-CoV-2 from presymptomatic and asymptomatic individuals. Single point in time estimates and binary PCR testing alone cannot provide reliable information on symptom status and information on infectivity. The number of studies and asymptomatic and presymptomatic cases eligible for inclusion was low, with more data and international standardisation of methods needed to further reduce uncertainty.