Weekly screening of healthcare workers and other at-risk groups could reduce their contribution to transmission by between 25-33%, a study published Thursday (23 April) by the WHO Collaborating Centre for Infectious Disease Modelling, concluded.
Using a mathematical model, the WHO study found that this could be achieved via polymerase chain reaction (PCR) or point-of-care tests for infection and, crucially, by testing irrespective of symptoms.
The research concluded that this could help reduce both transmission to and among this high-risk group, which compromises their own health and may also contribute to the spread of the virus.
The report points out that current testing strategies for health care workers often focus on testing symptomatic individuals, despite the fact that available data suggests that approximately 20- 50% of infections are asymptomatic.
It adds that, as it currently stands, the infectiousness of asymptomatic individuals is thought to be either equivalent to or lower than symptomatic infection, depending on the viral load, and that approximately 40% of transmission from symptomatic infections occurs before symptom onset.
Healthcare workers across Europe have been particularly vulnerable to contracting the virus due to their exposure to infection from patients and fellow staff.
It is estimated that they comprise between 4% and 19% of all reported COVID-19 cases in Europe and China.
In Italy, health care professionals have been especially hard hit, with 150 Italian doctors dying from the virus to date.
The report coincides with the UK’s recent decision to make testing for coronavirus available to millions of key workers and their families, having come under fire in recent weeks for its low testing rates.
In an article on the Imperial College London website, study author Professor Nicholas Grassly said that there had been “substantial pressure on the UK government and others to ‘test, test, test’ in response to the COVID-19 pandemic.”
However, he stressed that the research found that “testing is most useful when targeted at high-risk groups such as healthcare and care home staff.”
The observation that countries with high rates of testing for COVID-19, such as in South Korea and Germany, have more effectively controlled transmission has led to calls for increased testing in other countries with lower rates of testing.
The World Health Organisation has also called for increased molecular testing in response to the COVID-19 pandemic.
However, the optimal allocation of limited testing resources is still under debate. As increased testing resources become more widely available, it is becoming important to determine the role of wider testing in different population groups, both to monitor the epidemic and prevent transmission.
The model found that widespread testing in the general population was unlikely to limit transmission more than contact-tracing and quarantine based on symptoms alone, but it concluded that it could allow earlier release of contacts from quarantine.
For example, it suggests that ‘immunity passports’ based on tests for antibody or infection could support the return to work, but the report’s authors say that these face significant technical, legal and ethical challenges.
[Edited by Benjamin Fox]