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Pre-asymptomatic COVID cases lead to half of transmissions, study finds
Presymptomatic and asymptomatic COVID-19 cases contributed to at least 50% of transmissions during the first outbreak of COVID in New York City, according to a study published yesterday in Proceedings of the National Academy of Sciences.
The researchers applied a stochastic epidemiologic model that incorporated daily changes in testing capacity to New York City cases and serologic data from March 1 to June 1, 2020 and March 8 to April 19, 2020, respectively. Although asymptomatic transmission rates are still unknown, researchers report that both asymptomatic and symptomatic cases had reproduction rates of at least 3 in each reasonable simulation – above the estimated rate of 2 to 3 reported in many cities. where interventions were already in place. (Reproduction rates are the number of secondary cases caused by a primary case.)
While asymptomatic infections are transmitted at rates similar to symptomatic infections, they write, the reproduction number for all COVID-19 cases is 3.2 to 4.4. However, if asymptomatic infections are transmitted at a lower rate, symptomatic cases may have a reproductive value of 3.9 to 8.1, which could support more widespread observations.
Policies and test data should be more transparent to strengthen epidemiological models, the researchers write. “Testing only symptomatic cases can lead to at least a fourfold increase in IFR [infection fatality ratio] this is calculated, “write the researchers.” Limitations in testing capacity can also impact the estimated IFR.
As for New York City, the results indicated that COVID-19 transmissions began in February, which could be attributed to either the delay between the onset of infection and hospitalization, or an effect depending on the dose in which more contacts with SARS-CoV-2 could lead to a higher severity of the disease. The researchers also found that when the city implemented its lockdown, the COVID transmission rate dropped from 76.0% to 87.6%.
Even though the study could only estimate reproduction rates, the researchers say, “The consistent strong contribution to community transmission of symptom-free cases seen in the data-supported scenarios should be taken into account when formulating the results. public health intervention strategies.
Feb 10 Proc Natl Acad Sci to study
Allowing for chills, other symptoms of COVID-19 may optimize testing
While fever, cough, loss of smell, and loss of taste are the four classic symptoms of COVID-19, data from the REal-time Assessment of Community Transmission (REACT) study indicates that approximately 60% of infected people do not have these symptoms in the week before their test.
The study, published yesterday as an unpaired pre-print by Imperial College London, used swab and questionnaire data samples from 1,147,349 UK residents aged 5 and older. The researchers found that from June to December 2020, the presence of one of the classic symptoms had a positive predictive rate of 5.5% and that experiencing any of the other 22 symptoms had a positive predictive rate of 0.8%. In January 2021, when B117 accounted for about 86% of cases, classic symptoms had a positive predictive rate of 20.7% and other symptoms had a predictive rate of 2.5%.
Overall, chills were a common symptom at all ages, but the less absolute narrowing and operator stability selection also indicated that certain age groups were more likely to display headaches. head (children 5 to 17 years old), loss of appetite (18 years and over), and muscle pain (18 to 54 years). When comparing pre- and post-B117 dominance, the researchers noted that the presence of the variant may have increased the prevalence of cough and decreased the prevalence of loss of smell.
The researchers say that if all people with at least one classic symptom were tested, only 55% of all symptomatic cases would have been identified by January 2021. If the testing strategies were adapted to reflect the results of the stability screening, 76% of all symptomatic cases were identified in January.
“The approximately 40% increase in case detection (above that of at least one in four symptoms) would imply a 2.7-fold increase in the number of tests allocated to the symptomatic population in England,” write the researchers.
“These new findings suggest that many people with COVID-19 will not be tested – and therefore will not be self-isolating – because their symptoms do not match those used in current public health recommendations to help identify the infected people, ”Paul Elliott, MBBS, PhD, said in an article from Imperial College London.
February 10 Imperial College London to study
February 10 Imperial College London item
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