To defeat a pandemic, no single strategy is effective on its own. India has done well in implementing early lockdown and social distancing measures, as well as in screening and tracking visitors from high-risk countries. However, only when all proven strategies combine together can we expect a good outcome. 

For instance, even a single person, without any symptoms, is capable of spreading the SARS-Cov-2 virus to large numbers of people. Without widespread testing, such people cannot be identified. To prevent this fast-spreading virus from taking control of the community, we need to test, detect and isolate every case. If active community testing is not done, it is impossible to estimate the true extent of the spread of the virus, and the effort taken during lockdown would be wasted.

In spite of making significant progress in the recent past, India’s testing rates remain low. Germany’s testing rates are well over 100 times that of India. South Korea tests 75 times more people than India, and Britain’s testing rate is 30 times greater. 

Lack of adequate testing leads to a false sense of security, that can lead to uncontrollable spread. This will prove to be more expensive in the long run. This is the time to ramp up testing at a community level.

What are the types of tests for COVID-19?

There are two types of testing.

1. PCR test, also called RT-PCR, for identifying viral RNA in a throat swab sample. 

2. Rapid test, for detecting the presence of antibodies in a blood sample.

What are the logistical difficulties with PCR testing?

PCR testing involves obtaining a swab from the throat using protective equipment and precautions and transporting it safely to the designated lab. The presence of viral RNA is then confirmed using an RT-PCR machine.

The testing equipment is expensive, and the test needs to be done in a lab that has Biosafety level 2 or higher rating. This is a category of the lab that is specially equipped to prevent the spread of certain infectious diseases from the submitted specimens.

Most major cities have labs that have the capacity to do a PCR test. Some of these labs are also located in private centres. 

However, at present, this test is only being done in a few select centres, where the patient needs to be referred to. The criteria of testing have so far been limited. This made testing cumbersome. For instance, the average number of COVID-19 RT-PCR tests being done in Kerala is only about 700 per day.

Testing is now being expanded to more centres and is expected to involve the private sector too.

Until recently, PCR testing was done using primers provided by ICMR. This used to take 5-6 hours for the report. Recently, several private companies have developed rapid PCR kits. Twenty of these, made by various manufacturers, have already been approved by ICMR. This has decreased the report generation time to 3 hours.

How to improve our RT-PCR testing strategy?

ADVERTISEMENT

As greater numbers of people are being infected, what is now required is to provide testing ability at the point of care, that is at each hospital. This need not necessarily involve the purchase of additional equipment. Based on clinical suspicion, the doctor should be able to order a PCR test.

A throat swab taken on the spot by trained personnel could be sent to the nearest participating biosafety level-2 lab through a designated carrier. Results may be obtained within a day or two.

The advantage of this strategy is that each hospital does not have to invest in expensive equipment or infrastructure. To increase overall testing capacity as the disease spreads, more labs in each district must be drafted to do the PCR testing. 

Antibody test (Rapid test)

The next type of test is called antibody testing. Antibodies are substances produced by the immune system in response to an infection. Two types of antibodies are tested for IgM which is part of immediate response, and IgG, which is a delayed response antibody that is believed to confer long-term immunity against the virus. The antibody can be detected either by ‘card-test’ or by ELISA. 

The ‘card test’ is a bedside test done at the point of care, using a drop of blood. It works almost like a urine pregnancy test. It does not require a lab or intensive training of personnel. The results would be ready in 10-30 minutes

The ELISA test involves the use of machines that are commonly used in almost all diagnostic labs. The report takes 2-3 hours.

Who needs the antibody test? Is it accurate?

As a cheap and rapid diagnostic tool that does not require expensive infrastructure or equipment, antibody testing can be used to detect SARS-Cov-2 infection. 

Once they are made available, these tests can be performed at almost all hospitals. 

It must be noted that although IgM levels start rising in the first week, the test is more likely to turn positive in the second week of infection. Thus, antibody tests are relatively less useful for early detection, that is when done during the first week of illness. PCR test has a higher sensitivity than antibody detection during the first week.

In contrast, however, in the case of a patient with pneumonia, where the disease has already entered at least the second week, the antibody levels will be higher. In such a patient, testing for antibodies is a quick and easy way of ascertaining the diagnosis. 

Unlike IgM antibodies, IgG levels rise only later in the course of the infection. By the second week, just over 50 per cent of patients are positive, the levels reaching 80 per cent by the third week.

In the long term, IgG levels tell us how many people are immune to this disease due to recovery from past infection. For epidemiological purposes, IgG levels can also be used to estimate the extent of spread of the pandemic in a region. 

A potential future use of this test will be to identify those individuals who can be safely sent to take care of COVID positive patients. This is because it is unlikely that they would get SARS-Cov-2 infection again. 

Although not fool-proof, antibody testing is cheaper and less cumbersome than PCR. Besides, it does not require a BSL-2 lab. ICMR has already authorised the use of antibody testing.

ADVERTISEMENT

Which test is better? PCR or Antibody?

Although PCR testing is the most reliable and validated test available, this needs to be supported by the widespread use of antibody-based point-of-care ‘rapid’ testing as discussed above. 

The difference between the two strategies can be compared to the distinction between using an ultrasound scan and an MRI to look for a liver tumour. The ultrasound is used as a screening tool as it is reliable, inexpensive, and freely available. In contrast, the MRI has greater accuracy but requires substantial equipment and infrastructure. In effect, the two imaging modalities complement each other.

How to keep healthcare staff and hospitals safe?

It is also important to do regular surveillance of healthcare personnel. This includes testing doctors and nurses who work in busy clinical settings, to confirm that they are not at risk of spreading the virus.

Early testing will identify those at risk and help isolate them before they unknowingly spread the infection to colleagues and other patients at the facility.

All over the world, healthcare workers are getting infected, and many are succumbing to the infection. In Italy alone, over 100 doctors have died from COVID-19. The main reason is that they are not using adequate protective measures, partially from shortage and also because they are unaware of who is carrying the virus around them.

As a result, large hospitals have had to be closed down in cities like Bangalore, Mumbai and also in other countries. This brings down the efficiency of any healthcare system.

How does community testing help?

Testing, when made widely available, will complement the ongoing lockdown measures. It will help identify and contain disease hotspots early.

Accurate mapping of such areas can help customise lockdown measures to such hotspots, instead of blindly prolonging it in all areas. Once containment is reliably achieved, lockdown measures in other areas could even be relaxed sooner.

Systematic screening needs to be carried out wherever there is a perceived chance of infection. It can be centred around focused groups such as non-healthcare personnel who are in contact with the general public, or at healthcare establishments, where the concentration of virus is expected to be greater.

Measures are already being initiated in that direction. The lockdown is estimated to cost India about $4 billion every day.

Even if it can be relaxed partially, savings could be substantial. But the lifting of lockdowns must be done only if we can ensure that it is safe to do so. That can be only achieved through widespread community testing.

As Dr Tedros Adhanom, Director-General of WHO says: “you cannot fight the virus if you do not know where it is”.

Lifting the lockdown without meticulously studying the level of spread of the virus in the community will be like attempting to open the door of a submarine without verifying whether it has reached the sea’s surface.

ADVERTISEMENT

Thus, in the long term, the amount of money spent on widespread community testing could be substantially less than the amount lost by prolonging shutdown measures.

(Dr Rajeev Jayadevan is a senior consultant gastroenterologist and deputy medical director, Sunrise Group of Hospitals.)