Largest COVID-19 study highlights the role of super-broadcasters


In the Dhoom ranking of the worst COVID-19 outbreak, the United States, with 7.2 million infections, is only likely to be eclipsed by India, with 1 million fewer cases but catching up fast.

Yet some parts of India have led the world in one aspect of the epidemic response: contact tracing – labor-intensive, time-sensitive, the laborious task of identifying people exposed to a known infected person.

Extensive contact in the two southern Indian states, according to a study published Wednesday in the journal Science, offers the strongest evidence yet that some super-dispersed individuals are responsible for a proportionate share of new coronovirus infections. It also suggests that children are more efficient transmitters of the virus than is widely believed.

A team of Indian and American researchers examined data from 575,071 individuals who were tested after being exposed to 84,965 people with confirmed cases of COVID-19. This is an average of seven contacts per case, and a cohort 10 times larger than a previous study in South Korea that mapped how the virus was transmitted.

The lead author of the Center for Disease Dynamics, Economics and Policy in New Delhi, Ramnarayan Laxminarayan, said, “This is the largest epidemiological study anywhere on COVID so far.”

Lakshminarayan and his colleagues found that only 8% of people with COVID-19 had 60% of new infections in their contacts. Meanwhile, 7 out of 10 COVID-19 patients were not associated with any new cases.

The discovery underscores the essential role of super-spreaders in the COVID-19 pandemic: an individual or event, such as in a poorly ventilated indoor location, can trigger a high number of new infections, while transmitting other viruses at all Can.

In the new study, researchers tracked 78 people who shared a bus or train with one of the eight known infected people and sat within three rows of that person for more than six hours. Health workers visited these contacts in their homes to conduct follow-up investigations and determined that about 80% of them had contracted coronavirus.

In contrast, people who were known to be exposed to infected individuals in low-risk environments – such as in the same room but more than three feet away – became infected only 1.6% of the time.

Lakshminarayan said, “Super spreading events are the rule rather than the exception.” “This modeling has a lot of implications for COVID, to preserve locations.”

Studies show that super-spreading events are influenced by behavior – proximity to an infected person, length of contact, and ambient conditions determine the level of risk. It does not investigate whether some infected people spread the virus more efficiently due to biological factors, a question scientists are still trying to answer.

The results may help direct safety measures in gym, churches and choir practice locations that have been the location for previous super-spreading events.

People wait for their results of COVID-19 test at a government hospital in New Delhi

People await the results of their COVID-19 tests at a government hospital in New Delhi.

(Manish Swaroop / Associated Press)

The study also found that although children under the age of 17 were the least likely to die of COVID-19, they transmitted the virus at similar rates to the rest of the population, underscoring the idea that the disease could be passed on to young people Does not leave. One data point specifically has implications for reopening schools: children between the ages of 5 and 17 approached the virus at around 18% of their own age.

Antonio Salas, a Spanish researcher who has investigated the role of super-failures in the epidemic, said the study’s findings in relation to children were important in light of “suggesting a smaller role of children in the epidemic”.

“National policies to move forward with children in schools and other social activities can change dramatically if scientific evidence underpins the idea that children can infect as efficiently as adults, and more than that, they are super Can also behave as spreaders, ”said Salas, who was not involved in the study of India.

As India’s coronavirus caseloid has grown from 3 million to more than 6 million in the past month, the study authors said their work showed a strength of the country’s response: a large number of health workers and civil servants with contact tracing Ability to operate Identify high-risk individuals and watch their cases closely.

The two Indian states included in the study, Andhra Pradesh and Tamil Nadu, have a total population of 128 million and have some of the country’s largest healthcare workforce and the highest levels of public health spending. Both turned to disease-surveillance networks planted years ago during the AIDS epidemic to conduct door-to-door investigations at unseen levels worldwide.

In Tamil Nadu, which included the coastal metropolis of Chennai (formerly known as Madras), thousands of public and private health workers were trained as liaison coaches and health monitoring officers. The state had experience in identifying risk-related populations from its fight against AIDS, which made Tamil Nadu more difficult than anywhere in the country.

Once a person tested positive for coronavirus, a public health worker interviewed him over the phone to find out where and whom he had met in the past two weeks. Members of the immediate family were tested and separated immediately; Others were located via phone calls and text messages.

Almost all of the contacts traced were people known to the infected person, so many strangers were missed. Nevertheless, in Chennai, health workers tested an average of 17 contacts per infected person on 1 August.

Although contact tracing is important for identifying, isolating, and testing people susceptible to infection – and helping countries like South Korea avoid devastating outbreaks – an effective system has led to a shortage of trained staff and funds from the US Most parts of have been removed.

LA County’s contact tracing program has failed to prevent major outbreaks and may be caused by language barriers, slow turnaround times for test results, and inaccurate information from patients. The county has hired approximately 2,600 contact trainers to cover a population of 10 million. Chandra Mohan, a state official, said Madurai, a semi-urban district in Tamil Nadu, had health workers equivalent to one-third of the population who helped the response and was co-author of the study.

Although poorer nations now record most of the world’s COVID-19 cases, most of which came from a relatively small-scale study of how the coronavirus spreads, among the wealthier nations of China, America, and Europe. is.

India imposed the tightest lockdown anywhere in late March, which found that the new study significantly slowed the spread of the virus. As Prime Minister Narendra Modi’s government has relaxed restrictions to revive the economy, not disease, has surprisingly resurfaced. But Mohan said the contact tracing program saved lives.

Tamil Nadu has recorded around 600,000 infections and 9,400 deaths, which is 13 deaths per 100,000 people. The US COVID-19 death rate is approximately 62 per 100,000.

“What is needed is clarity of thought and ability to mobilize and use resources,” Mohan said. “I think a good governance framework makes the difference between what can be done and what cannot be done.”

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