Mass asymptomatic COVID-19 testing program reduced hospital admissions

A voluntary mass testing program for individuals without COVID-19 symptoms was associated with a reduction in COVID-19-related hospital admissions, a study published in BMJ found.

Asymptomatic COVID-19 transmission has been a “major challenge” throughout the pandemic, Xingna Zhang, PhD, a research associate in the department of public health, policy and systems at the University of Liverpool, and colleagues noted.

“Modeling studies based on the original strain had suggested that more than half of transmissions in the community may arise from people without symptoms, whether pre-symptomatic or never symptomatic,” they wrote.

To identify asymptomatic cases, many countries have implemented rapid SARS-CoV-2 antigen testing with lateral flow devices, according to the researchers. There has been debate over their use, including the potential harms of false-negative and false-positive results. However, the researchers noted that these debates have “lacked controlled comparisons of key outcomes such as hospital admissions for tested versus untested populations experiencing concurrent pandemic phases, with comparable patterns of virus variants and population immunity.”

To determine the effectiveness of mass testing, Zhang and colleagues examined weekly COVID-19-related hospital admissions among participants of Covid-SMART, a citywide voluntary pilot program conducted in Liverpool, England, from Nov. 6, 2020, to Jan. 2, 2021. The program offered supervised self-testing with the Innova SARS-CoV-2 rapid antigen lateral flow device to individuals without COVID-19 symptoms.

The analysis included 498,042 individuals who lived or worked in Liverpool. Throughout the study period, Liverpool’s total COVID-19 case count increased from 21,000 to 31,163, according to the official U.K. government website.

Hospital admissions, an outcome chosen by Zhang and colleagues because they are “less affected by changes in levels of case detection than other outcomes,” were analyzed between Nov. 19, 2020, to Jan. 15, 2021. They were then compared with weekly COVID-19-related hospitalizations in 6,290 neighborhoods in England outside of Liverpool during the same period.

The researchers found that during the initial testing period from Nov. 6, 2020, to Dec. 3, 2020, hospital admission rates in Liverpool were 43% (95% CI, 57-29) lower compared with control areas.

When the analysis was extended to Jan. 2, 2021, Liverpool admission rates were 16% (95% CI, 27-0) lower compared with control areas. However, when adjusted for “very high alert” city restrictions, Zhang and colleagues reported a reduction of 25% (95% CI, 35-11).

The researchers wrote that if the effect is causal, the isolation of 5,110 individuals who tested positive in Covid-SMART prevented around 6,829 infections.

The researchers highlighted several limitations to the study, which included concurrent changes in intervention and control populations that could produce bias. Data were also collected on neighborhoods, and not individuals or household characteristics.

Zhang and colleagues partly attributed the high reduction rate during the initial rollout period to a greater intensity of testing due to military presence. They concluded that mass testing may help to reduce COVID-19 transmission and additional risks, but “the success of such control measures relies on high levels of uptake and effective support to enable isolation of infectious people and their close contacts.”

References:

• Cases in Liverpool. https://coronavirus.data.gov.uk/details/cases?areaType=ltla&areaName=Liverpool. Accessed Nov. 28, 2022.
• ‘Mass testing’ linked to 25% cut in COVID-19 related hospital admissions. https://www.eurekalert.org/news-releases/972108. Published Nov. 23, 2022. Accessed Nov. 28, 2022.
• Zhang X, et al. BMJ. 2022;doi:10.1136/bmj-2022-071374.