A new method to control epidemics such as COVID-19 provides an accurate real-time estimate of the growth rate of an epidemic by carefully assessing the relationship between the amount of virus in the body of infected people, called viral load, and the speed with the cases increase or decrease.
“This new method, which effectively links what we know about how the virus grows in the body and the dynamics of how the virus spreads to the entire population, provides a new metric that public health officials, policymakers, will be able to do. and epidemiologists. use it to get up-to-date real-time information about the epidemic, “said Michael Mina, assistant professor of epidemiology at Harvard TH Chan School of Public Health and a core member of the Center for Dynamic Disease Dynamics.
Mina is the lead author of an article describing the method, published on June 3, 2021 in the journal Science.
Control of epidemics is essential for the response to public health to understand the functioning of interventions such as masks, closures or vaccines and to know where additional resources are distributed as cases increase.
He current approaches to control epidemics they rely almost entirely on monitoring the number of cases or hospitalization rates over time, and on reviewing test positivity and mortality rates. Throughout the COVID-19 pandemic, for example, daily data from cases such as that published by The New York Times has been crucial for public health officials and researchers to assess the extent to which states and countries control the spread of the SARS-CoV-2 virus caused by COVID-19. However, this type of data can often only be of limited use due to variable testing practices or poor reporting. For example, a growing epidemic might appear to be stagnating if test capacity is maximized or if notification is delayed because resources are being concentrated elsewhere. These pitfalls of tracking case reports over time can negatively affect appropriate public health responses.
Because outbreaks grow or fall exponentially, as cases grow, most positive people at any given time will have been recently infected and will therefore have higher viral loads — as measured in PCR tests (chain reaction). polymerase) – at the time they are tested. This is because the virus is at its peak in the body early after infection and then falls to very low but still detectable levels in PCR tests for weeks or even months after infection. When the outbreak slows down and cases decrease, the average person detected as positive on surveillance tests will have potentially become infected weeks before the test and will therefore have lower viral loads at the time of the outbreak. test.
To better track pandemic hotspots, researchers at Harvard Chan School developed a mathematical tool that carefully assesses the relationship between viral load—Measured from the PCR test at a value called the cycle threshold (Ct value) —and the rate at which cases increase or decrease. Using even the relatively small number of 30 positive SARS-CoV-2 surveillance samples taken in a single day can give an accurate real-time estimate of the growth rate of the epidemic. When Ct values are available from various time points, the researchers found that they can use even a very limited amount of positive results to reconstruct the epidemic curve and estimate how many people have become infected over time. of time.
Even viral amounts detected in positive PCR test samples collected from a site at a single time can help estimate the growth or decay rate of an outbreak in a population, the researchers found.
In the US and much of the world, Ct PCR values, values that show how much virus it is collected in the swab of someone’s nose: they are often discarded and the results of the PCR test are returned with a simple “positive” or “negative” result.
“Our work demonstrates the value of Ct values and why we should not only stop our current practice of throwing them away, but why we should turn them into a key piece of data to collect for our pandemic response, “said Mina, who has previously published on the use of PCR Ct values to aid clinical decision-making and who has been a leader in developing new approaches to using COVID-19 testing for limit the spread of the disease.
James Hay, who co-led the research as a postdoctoral researcher at Mina’s lab, stressed that the new technique is not specific to COVID-19, but is a method that will be valuable for tracking outbreaks and epidemics of other viruses. in the future. “This tool is not just for COVID, but provides a new approach to estimating epidemic trajectories of many types of viruses, and it is an approach that does not depend on potentially biased approaches, such as counting cases over time and that will not depend on accurate case notification or hospitalization, ”he said.
“Estimation of epidemiological dynamics from transverse viral load distributions”, Science (2021). science.sciencemag.org/lookup/… 1126 / science.abh0635
Harvard TH Chan School of Public Health
Citation: The new real-time control method accurately reflects the hot spots of the epidemic (2021, June 3) recovered on June 4, 2021 at https://medicalxpress.com/news/2021-06-real- time-method-accurately-hotspots-epidemic.html
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