freemexy: Study suggests undetected cases help speed COVID-19 spread

Study suggests undetected cases help speed COVID-19 spread


4 Aug 2020 at 08:08am
Study suggests undetected cases help speed COVID-19 spread



A modeling study looking at more than 32,000 confirmed coronavirus cases in Wuhan, China, offers fresh insights into features of the virus, including ease of transmission, effectiveness of nonpharmaceutical interventions such as social distancing and face masks, and the impact that undetected cases have on the spread of the disease.To get more news about coronavirus wuhan, you can visit shine news official website.
The analysis, published in the journal Nature, underscores the stealthy nature of the virus and adds to a growing body of research that suggests people infected with COVID-19 who went undetected or were asymptomatic, presymptomatic, or had only mild symptoms have been significant spreaders of the disease.

Using statistical and epidemiological modeling to reconstruct the outbreak in Wuhan from Jan. 1 to March 8, researchers found that up to 87 percent of cases in the city during that time may have gone undetected and transmission rates during some of the earliest days could have been as high as 3.54 infections per single case. (A rate above 1 signifies rising spread.) It’s a figure that was only controlled because of widespread and strict containment measures and lockdowns, hammering home the importance of interventions like face masks even in curtailing undetected infections, according to the paper.

The researchers, including Harvard Professor Xihong Lin and a team of scientists from Huazhong Science and Technology University in Wuhan, believe that undetected infections — from sources including people who were asymptomatic, presymptomatic, or had only mild symptoms — likely played a substantial role in the fast spread of the disease and could become one of the leading factors for a possible second wave of infections if restrictions are lifted too early.

“There are important consequences to those undetected cases,” said Lin, a professor of biostatistics at the Harvard T.H. Chan School of Public Health and a professor of statistics at the Faculty of Arts and Sciences. Put simply: “Even though they are undetected, they are still infectious. It’s important to avoid reopening too early without vigilant control measures, because when the number of detected cases is not low, the numbers of undetected cases, or unascertained cases, are not low either. They are even bigger.”

The study comes as nations around the world battle to control their outbreaks. Some have been sliding backward. Many states in the U.S., for instance, have seen record surges after reopening before the outbreak was reined in. California on Monday announced major rollbacks, closing gyms and museums and halting indoor dining at restaurants.You can see there are several countries, including the U.S, Australia, and Spain in the last month, that have observed resurgences, and some of those countries did really well in April and May,” Lin said.

The paper builds on the researchers’ earlier work, released on a preprint server in early March and published in the journal JAMA in April. In mid-April Lin presented much of the group’s findings to the U.K. Parliament’s Science and Technology Committee, which wrote a letter to Prime Minister Boris Johnson with 10 findings and recommendations. Lin also served on Massachusetts’ COVID-19 task force in March. In June, her lab launched a website that allows users to check multiple COVID-19 metrics of countries all over the world as well as U.S. state and county levels in real time.

With the study, researchers wanted to better understand how easily the virus spreads, the number of undetected cases, their effects during an outbreak, and the efficacy of containment measures. They decided to look at the full transmission dynamics of the virus in Wuhan, the original epicenter, where strict restrictions effectively suppressed the outbreak.The researchers examined 32,583 laboratory-confirmed coronavirus cases from Dec. 8, 2019, until March 8, 2020. They divided the dates into five time periods based on key events and interventions, such as the implementation of mandatory centralized isolations and quarantines of people infected or suspected of being infected.

The scientists found that the initial rate of transmission in Wuhan was very high but that it dropped considerably as multifaceted control measures were enacted. They estimate the number of new infections stemming from a single case (called the R0 but pronounced “R-naught”) was about 3.54 in the earliest period from Jan. 1 to 9. The second period, from Jan. 10 to 22, which saw a large influx of visitors to the city for Chinese New Year, also had a high transmission rate of about 3.32. The third, fourth, and fifth periods coincided with strict lockdowns followed by centralized isolations, quarantines, and universal screening, which resulted in declines to 1.18, 0.51, and 0.28, respectively. The figures represent a 96 percent drop from late January to early March.


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