8/17—Masks Protect the Wearer by Reducing Dose of SARS-CoV-2
I am back after a week off with less recent (but important) studies. It seems masks may protect the wearer, and that serological tests are not ready for prime time. I will resume curating new studies tomorrow.
Masks Do More Than Protect Others During COVID-19: Reducing the Inoculum of SARS-CoV-2 to Protect the Wearer
We discuss for one of the first times the hypothesis that universal masking reduces the “inoculum” or dose of the virus for the mask-wearer, leading to more mild and asymptomatic infection manifestations. For example, [in a recent] cruise ship outbreak, all passengers were issued surgical masks and all staff provided N95 masks […]. The majority of infected patients on the ship (81%) remained asymptomatic, compared with 18% in the [Diamond Princess cruise ship] outbreak without masking. A report from a pediatric hemodialysis unit in Indiana, where all patients and staff were masked […] none of the new infections was symptomatic. And in a recent outbreak in a seafood processing plant in Oregon where all workers were issued masks each day at work, the rate of asymptomatic infection among the 124 infected was 95%. An outbreak in a Tyson chicken plant in Arkansas with masking also showed a 95% asymptomatic rate of infection (Gandhi et al. 2020).
Drug treatments for covid-19: living systematic review and network meta-analysis
23 randomised controlled trials were included in the analysis performed on 26 June 2020. Glucocorticoids were the only intervention with evidence for a reduction in death compared with standard care (risk difference 37 fewer per 1000 patients, 95% credible interval 63 fewer to 11 fewer, moderate certainty) and mechanical ventilation (31 fewer per 1000 patients, 47 fewer to 9 fewer, moderate certainty). Three drugs might reduce symptom duration compared with standard care: hydroxychloroquine (mean difference −4.5 days, low certainty), remdesivir (−2.6 days, moderate certainty), and lopinavir-ritonavir (−1.2 days, low certainty). Hydroxychloroquine might increase the risk of adverse events compared with the other interventions, and remdesivir probably does not substantially increase the risk of adverse effects leading to drug discontinuation.
Diagnostic accuracy of serological tests for covid-19: systematic review and meta-analysis
5016 references were identified and 40 studies included. High risk of patient selection bias was found in 98% (48/49) of assessments and high or unclear risk of bias from performance or interpretation of the serological test in 73% (36/49). The pooled sensitivities had a wide range, with higher sensitivity in the CLIAs (97.8%) and lowest in the LFIAs (66.0%) and were higher with increased time after symptom onset. The range for specificities was narrower, from 96.6% to 99.7%. The available evidence on the accuracy of serological tests for covid-19 is characterised by risks of bias and heterogeneity, and as such, estimates of sensitivity and specificity are unreliable and have limited generalisability. Evidence is particularly weak for point-of-care serological tests. Caution is warranted if using serological tests for covid-19 for clinical decision making or epidemiological surveillance.
Antibody tests for identification of current and past infection with SARS‐CoV‐2
We had concerns about risk of bias and applicability. Pooled results for IgG, IgM, IgA, total antibodies and IgG/IgM all showed low sensitivity during the first week since onset of symptoms (all less than 30.1%), rising in the second week and reaching their highest values in the third week. The combination of IgG/IgM had a sensitivity of 30.1% (95% CI 21.4 to 40.7) for 1 to 7 days, 72.2% (95% CI 63.5 to 79.5) for 8 to 14 days, 91.4% (95% CI 87.0 to 94.4) for 15 to 21 days. At a […] prevalence of 5%, a likely value in national surveys, 4 (3 to 7) would be missed per 1000 tested, and 12 (6 to 27) would be falsely positive. Concerns about high risk of bias and applicability make it likely that the accuracy of tests when used in clinical care will be lower than reported in the included studies.
Meta-analysis of diagnostic performance of serological tests for SARS-CoV-2 antibodies up to 25 April 2020 and public health implications
Random-effects models yielded a summary sensitivity of 82% for IgM, and 85% for IgG and total antibodies. For specificity, the pooled estimate were 98% for IgM and 99% for IgG and total antibodies. In populations with ≤ 5% of seroconverted individuals, unless the assays have perfect (i.e. 100%) specificity, the positive predictive value would be ≤ 88%. Serological tests should be used for prevalence surveys only in hard-hit areas.
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