Article by Dr Vishad Viswanath MD (Gen Med), DM (Clinical Immunology)
Till date, India has not declared community spread in connection with COVID-19. However, many news reports indicate that at least in a couple of cases, the infection has occurred in persons with no known primary contact. In this scenario, despite the best of our efforts, it could be inevitable that our community might be exposed to the virus eventually, if that has not already happened. Why is this so? To understand this, we need to take into account the viral dynamics as well as the limitations of the current measures used in tackling the infection.
Dynamics of a viral infection:-
The capacity of a virus to cause human disease can be attributed to three factors; the amount of virus that one is exposed to (viral load), aggressiveness of the virus in establishing a human infection, and the ability of the host to prevent viral infections (also called immunity). So when a virus comes in contact with humans, it could take the following course -
1. Aborted infection - The virus comes in contact with the individual, but the immune system resists entry of the virus into our body. These cases do not spread the infection further.
2. Asymptomatic infection - The virus enters the body and even establishes the infection; however due to effective immune response, the virus does not cause any symptoms to manifest. Although asymptomatic, the virus is present in the person’s body; he/she can potentially spread and cause infection to others.
3. Symptomatic Infection - The virus enters and establishes infection in a person. This occurs after an incubation period which is the time taken by the virus to multiply in adequate numbers to cause the host to develop symptoms. In the case of COVID-19, the incubation period is 2 - 14 days (an average of 5 days). Some viruses can spread the infection even before becoming symptomatic, i.e. during the incubation period itself. A simple example is chicken pox, where an infected person can spread the infection up to 2 days before the onset of rash.
In the case of COVID-19, studies from China and Italy seem to suggest that the virus can start spreading up to 2 days before the onset of symptoms. What is even more striking is that, cases with asymptomatic infections are also known to harbor the virus and can shed it, although the amount of virus they shed may be less than a symptomatic person. So here are two situations where a person harbors the infection and can still spread it even when he is asymptomatic especially if he is not in Quarantine or not respecting the principles of Quarantine
.
The second issue is related to sensitivity of the tests that are available. Current studies show that the sensitivity of a nasal or pharyngeal swab testing with the current testing methods, is 63%. The percentage of negative test report is even more so if protocol for sample collection and processing is not strictly adhered to ( Ideally a sample need be collected and send to lab in 3-4 hours for testing or transported at -20 degrees). However in Kerala, a specimen from nose and throat are collected together and sent for testing, which may slightly increase the sensitivity to say, 75%. In most cases, tests are being done in highly suspected individuals and that too at a single point only. The implication being that, with the currently available tests, even the best ones, we are still missing out on at least 25 % of all infected cases. Moreover, there have been reports from other parts of the world where a positive test was obtained only on repeated testing (i.e. 2 to 3 attempts).
The current Quarantine policy does not seem to account for this possibility of false negative test reports, as those with negative test results are released from quarantine. It may also be mentioned that we may be required to reconsider the Quarantine policy and ensure that those high risk individuals may continue to be in Quarantine till the period of infectivity even though one test comes as negative.
The aforementioned 2 factors along with the logistic implications of ensuring strict quarantine or isolation, make it likely that the community could be exposed to the virus sooner or later.
Does this mean we should press the panic button and change our strategy? No. Despite all shortcomings, thankfully Kerala and possibly India has not shown the exponential rate of increase in cases, defying the projections from experts, at least to this day. One can always say that we are not testing adequately and are under-representing the number of actual cases. However in the absence of wide testing, an increase in number of hospitalizations with COVID-19, like respiratory diseases or increase in death due to pneumonia in hospitals can be taken as surrogate markers for community infections. Nowhere in India has there been an increased report of these incidents. It could be that the cases who are COVID positive and potentially missed by the system(as mentioned before) may be less effective spreaders of the disease than those who are captured by the current testing strategies. So whatever we are doing seems to be working till now, therefore let us continue with the policy of quarantine and social distancing with continued vigor.
Article by Dr. VISHAD VISWANATH
MD (Gen Med), DM (Clinical Immunology)
IRIS Centre for Arthritis & Rheumatology
Address: RDS Melody Apartments
Opp Asian Bread Factory,
Pangappara, Thiruvananthapuram, Kerala 695581
Contact Number: +91 471 2412573; +91 8281445394
Email: info@irisclinics.com
Dynamics of a viral infection:-
The capacity of a virus to cause human disease can be attributed to three factors; the amount of virus that one is exposed to (viral load), aggressiveness of the virus in establishing a human infection, and the ability of the host to prevent viral infections (also called immunity). So when a virus comes in contact with humans, it could take the following course -
1. Aborted infection - The virus comes in contact with the individual, but the immune system resists entry of the virus into our body. These cases do not spread the infection further.
2. Asymptomatic infection - The virus enters the body and even establishes the infection; however due to effective immune response, the virus does not cause any symptoms to manifest. Although asymptomatic, the virus is present in the person’s body; he/she can potentially spread and cause infection to others.
3. Symptomatic Infection - The virus enters and establishes infection in a person. This occurs after an incubation period which is the time taken by the virus to multiply in adequate numbers to cause the host to develop symptoms. In the case of COVID-19, the incubation period is 2 - 14 days (an average of 5 days). Some viruses can spread the infection even before becoming symptomatic, i.e. during the incubation period itself. A simple example is chicken pox, where an infected person can spread the infection up to 2 days before the onset of rash.
In the case of COVID-19, studies from China and Italy seem to suggest that the virus can start spreading up to 2 days before the onset of symptoms. What is even more striking is that, cases with asymptomatic infections are also known to harbor the virus and can shed it, although the amount of virus they shed may be less than a symptomatic person. So here are two situations where a person harbors the infection and can still spread it even when he is asymptomatic especially if he is not in Quarantine or not respecting the principles of Quarantine
.
The second issue is related to sensitivity of the tests that are available. Current studies show that the sensitivity of a nasal or pharyngeal swab testing with the current testing methods, is 63%. The percentage of negative test report is even more so if protocol for sample collection and processing is not strictly adhered to ( Ideally a sample need be collected and send to lab in 3-4 hours for testing or transported at -20 degrees). However in Kerala, a specimen from nose and throat are collected together and sent for testing, which may slightly increase the sensitivity to say, 75%. In most cases, tests are being done in highly suspected individuals and that too at a single point only. The implication being that, with the currently available tests, even the best ones, we are still missing out on at least 25 % of all infected cases. Moreover, there have been reports from other parts of the world where a positive test was obtained only on repeated testing (i.e. 2 to 3 attempts).
The current Quarantine policy does not seem to account for this possibility of false negative test reports, as those with negative test results are released from quarantine. It may also be mentioned that we may be required to reconsider the Quarantine policy and ensure that those high risk individuals may continue to be in Quarantine till the period of infectivity even though one test comes as negative.
The aforementioned 2 factors along with the logistic implications of ensuring strict quarantine or isolation, make it likely that the community could be exposed to the virus sooner or later.
Does this mean we should press the panic button and change our strategy? No. Despite all shortcomings, thankfully Kerala and possibly India has not shown the exponential rate of increase in cases, defying the projections from experts, at least to this day. One can always say that we are not testing adequately and are under-representing the number of actual cases. However in the absence of wide testing, an increase in number of hospitalizations with COVID-19, like respiratory diseases or increase in death due to pneumonia in hospitals can be taken as surrogate markers for community infections. Nowhere in India has there been an increased report of these incidents. It could be that the cases who are COVID positive and potentially missed by the system(as mentioned before) may be less effective spreaders of the disease than those who are captured by the current testing strategies. So whatever we are doing seems to be working till now, therefore let us continue with the policy of quarantine and social distancing with continued vigor.
Article by Dr. VISHAD VISWANATH
MD (Gen Med), DM (Clinical Immunology)
IRIS Centre for Arthritis & Rheumatology
Address: RDS Melody Apartments
Opp Asian Bread Factory,
Pangappara, Thiruvananthapuram, Kerala 695581
Contact Number: +91 471 2412573; +91 8281445394
Email: info@irisclinics.com
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