Coming up trumps in the virus fight

Which country has performed the highest number of COVID-19 tests? The United States. Which country’s President said he is safe because everyone who meets him at work or attends a political rally is pre-screened by virus testing? Again, the United States. Unfortunately, U.S. President Donald Trump has now been infected by the novel coronavirus despite all that testing. While wishing him a speedy recovery, we must wonder why that formidable cordon of testing did not prevent the virus from sneaking through. Also, why is the U.S. the global leader in COVID-19 deaths while testing at such high rates? The answers are relevant to other countries.

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The ‘test’ strategy

Despite the belief that tests are the key to control of the pandemic (“Test! Test! Test!”), they are not infallible. They have inaccuracies arising from false negative and false positive results. False negatives mean that tests do not always detect the virus when present. This may be because the virus could not be picked by the swab early or late in the infection or that a defective sampling technique could not grab the virus. ‘Sensitivity’ is the ability of the test to detect the virus in persons who are truly infected. This is usually assessed in hospital cases where the diagnosis is highly probable on clinical criteria, as compared to persons who are judged to be virus free.

However, such ‘technical sensitivity’ is often higher than the ‘clinical sensitivity’ observed in field conditions, as pointed out in a recent paper by McAdam and Pettengill (“Can We Test Our Way Out of the COVID -19 Pandemic?”). Molecular tests such as real time RT-PCR (Reverse Transcription Polymerase Chain Reaction) have a real world sensitivity between 60-70%. The Rapid Antigen Tests (RAT), when tested against RT-PCR as the gold standard, have a sensitivity ranging from 50-90%, according to different estimates. So, if RT-PCR has a sensitivity of 70% and RAT has a sensitivity of 70% compared to it, we run the risk of missing half the infected persons with RAT.

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The other tests

While some manufacturers have claimed higher technical sensitivity with recent improvements, the rapid tests have been widely criticised for low sensitivity in field conditions. Yet, these are the tests that were used for screening officials, visitors and rally attendees who might pose a viral threat to the U.S. President.

Widespread use of tests for detection and isolation of infected cases, followed by tracing their contacts for testing and quarantine, with treatment of diagnosed cases, was promoted as the ‘Test-Trace-Treat’ formula by global and national health agencies. While this is conventional wisdom in infectious disease epidemics, the COVID-19 virus proved too tricky for this standard tackle. Asymptomatic and pre-symptomatic persons emerged as persons harbouring and discharging the virus. How many symptomless persons can we test in a large population, and how often?

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Even for guiding treatment decisions, the only drug that has emerged so far with life-saving potential in seriously-ill hospitalised patients is dexamethasone. Steroids are not specific to COVID-19 and their use is dictated mainly by clinical state and not the test result.

Have we set too much in store by the testing rates in the population? When neighbouring countries are compared in any geographic zone, with similar socio-demographic and environmental conditions, there is absolutely no correlation between tests per million and deaths per million. Why is the death rate in Canada much lower than in the U.S. which has tested at a much higher rate? Across the world, the scatter is even wider. In contrast to the emphasis on testing rates, the U.S. did not fare well in contact tracing. It failed to mandate masks and faltered in persuading people to wear them, sending mixed political messages and conflicting technical advisories on their use.

Mask use

Some of the delay resulted from global health agencies taking time to unequivocally recommend the universal use of masks, despite the experiential wisdom of East and South East Asian countries in using masks to combat earlier respiratory virus epidemics. Would the world have been in a better place today if the World Health Organization’s call in March was “Mask! Mask! Mask!’? Perhaps, the clarion call for testing reflected the understanding at that time. We are better informed now. Yet, many in the U.S. remain impervious to evidence and advice on masks.

The U.S. also paid little heed to social distancing. The fractious political environment bred contempt for public health advice and positioned opposition to masks and physical distancing as a libertarian assertion of personal freedom.

The fact that ‘Super Spreader’ events promote rapid dissemination of infection from a few infected persons to many others is well known from past epidemics of respiratory viruses. This is akin to the Pareto principle, propounded by the Italian-Swiss economist Vilfredo Pareto that roughly 80% of the effects in many events come from 20% of the causes. We now know that 5-20% of the infected persons are responsible for spreading the virus to 80% of others who are infected. Since this happens mostly in crowded ‘Super Spreader’ events (where people congregate or travel together), testing is either not always possible or does not pick up the virus in asymptomatic persons.

Yet, indoor crowding can form virus clouds from such persons in confined spaces, endangering many others. Here too, universal masking offers the best protection. If only we could roll the clock back and recommend universal masking in January or February 2020. If only the President of the United States had regularly worn a mask and told others to do so too.

Dr. K. Srinath Reddy, a cardiologist and epidemiologist, is President, Public Health Foundation of India (PHFI). He is the author of ‘Make Health in India: Reaching a Billion Plus’. The views expressed are personal

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Printable version | Jun 14, 2021 9:28:56 AM |

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