A new study published in the open-access journal PLOS Medicine by Diana Buitrago-Garcia at the University of Bern, Switzerland and colleagues suggests that true asymptomatic cases of SARS-CoV-2 comprise a minority of infections, medicalxpress.com reported.

The full spectrum and distribution of the severity of COVID-19 symptoms are not well understood. Some infected people may experience severe infections resulting in viral pneumonia, respiratory distress syndrome, and death, while others remain completely asymptomatic or develop mild, nonspecific symptoms.

To better understand the proportion of people who become infected with SARS-CoV-2 and never develop any symptoms, as well as the proportion of people who are asymptomatic at the time of diagnosis but develop symptoms later, researchers systematically reviewed literature using a database of SARS-CoV-2 evidence between March and June, 2020. The authors then analyzed 79 studies reporting empirical data on 6,616 people, 1,287 of whom were defined as asymptomatic, in order to determine the proportion of infected people who never developed symptoms. While the study was limited by its inability to ascertain the impact of false negatives, the researchers were able to estimate that 20 of COVID-19 infections remained asymptomatic during follow-up.

Accurate estimations of true asymptomatic and presymptomatic infections are critical to understanding SARS-CoV-2 transmission at the population level and for populations to adopt appropriately tailored public health strategies. Future research should include prospective longitudinal studies that document symptom status. Improved accuracy of serological tests is also needed to reduce the number of false negatives. Since each person infected with SARS-CoV-2 is initially asymptomatic, the proportion that will go on to develop symptoms is estimated to be around 80 percent, suggesting that presymptomatic transmission may significantly contribute to overall SARS CoV-2 epidemics.

According to the authors, “The findings of this systematic review of publications early in the pandemic suggests that most SARS-CoV-2 infections are not asymptomatic throughout the course of infection.

The contribution of presymptomatic and asymptomatic infections to overall SARS-CoV-2 transmission means that combination prevention measures, with enhanced hand and respiratory hygiene, testing and tracing, and isolation strategies and social distancing, will continue to be needed.

The study by Imperial College London showed the “lab-on-a-chip” gave comparable results to current tests, BBC reported.

The device is already being used in eight National Health Service (NHS) hospitals to quickly identify patients who are carrying the virus.

However, experts warn that the kit will not be a solution to the beleaguered Test and Trace program.

The device, developed by the company DnaNudge, can be used by anyone capable of taking a swab of the nose or throat.

The swab is placed inside a disposable blue cartridge which contains the chemicals needed for the test.

This in turn is slotted into a shoebox-sized machine to perform the analysis.

The study, published in the Lancet Microbe, compared results when samples from 386 people were given both the DnaNudge and standard laboratory tests.

“The performance was comparable, which is very reassuring when you’re trying to bring in a new technology,” said Professor Graham Cooke, from Imperial College London.

“Many tests involve a trade-off between speed and accuracy, but this test manages to achieve both.”

If the lab tests said the patient was free of the virus, so did the rapid test. If the lab tests said the patient had the virus, the rapid test agreed 94 percent of the time.

The UK has already ordered 5,000 of the Nudgebox machines and 5.8 million of the disposable cartridges.

However, there is a major drawback as each box can handle only one test at a time. So during a day, one box could perform around 16 tests.

Cooke said: “They are useful in clinical settings when you are trying to make a rapid decision.”

He described a patient last week who was rapidly identified as having COVID-19 and started on the drugs dexamethasone and remdesivir.

The tests could become even more useful for hospitals in the future as it is theoretically possible to test for coronavirus, flu and respiratory syncytial virus (a major reason young children are admitted to hospital) at the same time.

However, the capacity issue means the test cannot solve the problems with NHS Test and Trace or help with Operation Moonshot and the plans for 10 million tests per day.

Testing 60,000 people at a stadium ahead of a football match would require 60,000 boxes, but it may be useful at smaller venues.

Professor Lawrence Young, who was not part of the research and from the University of Warwick, said the technology was “innovative”.

He added: “The COVID Nudge test could have an important role where near-patient, real-time decision-making is necessary, such as screening patients for admission to hospital or for surgery.

“[However,] this is not the answer to universal mass testing.”