The COVID-19 has attained pandemic proportions with more than 200 countries affected. These countries have enforced strict lockdown measures to control this novel Coronavirus outbreak but without much success. The virus continues to spread rapidly because of its highly contagious nature.
The medical health workers are at the moment engaged in the collection of the samples, laboratory testing, and confirming the diagnosis of the COVID-19 suspects.
Testing for the novel Coronavirus (SARS-CoV-2 as WHO has named it) offers a panoramic view of the pandemic and how it is spreading, helping us to understand the outbreak and its risks on different populations.
It helps to devise ways to reduce the transmission of the virus and its impact on the world and the population. Testing helps identify infected individuals so that they and their contacts can be quarantined and treatment can be given whether prophylactic or curative.
A positive case of COVID-19 can only be confirmed by lab tests. The World Health Organization defines a confirmed case as “a person with laboratory confirmation of COVID-19 infection”.
Who should be tested?
The Center for Disease Control and Prevention (CDC) has prepared a list of people who should be tested based on priority.
The first on the list are the people with suspicion who are admitted to hospitals with COVID-19 symptoms and the healthcare workers who exhibit these symptoms.
People with a history of exposure to someone who has already been diagnosed with COVID-19 or those who have been to an area where there is an ongoing community spread of COVID-19 within the last 14 days are also high on this priority list.
Next on the priority list are the people who live in long-term medical facilities especially those over the age of 65 years or those with comorbidities such as high blood pressure, diabetes, cancer, heart, lung or kidney disease, and those on immune-suppression drugs.
Immune-suppression therapy is indicated in autoimmune diseases such as psoriasis, lupus, rheumatic arthritis, Crohn’s disease, multiple sclerosis, and in patients who have undergone an organ transplant.
First responders are also included in the 2nd list of priorities. Such people include personnel with law enforcement, fire services, emergency medical services, and emergency management officials, who come in close contact with persons with confirmed or possible COVID-19 infection during the course of duty.
Healthy young people who do not have any symptoms are the lowest priority on the list.
There are two kinds of tests for COVID-19:
- Reverse transcription-polymerase chain reaction (RT-PCR): These tests detect the presence of the virus in the person to establish whether he is infected;
- Serology tests: These tests detect the presence of antibodies in the blood that the body produces to fight the virus if the person has been infected in the recent past.
At present, PCR and antibody testing are the main ways that the worldwide healthcare bodies screen persons for COVID-19.
However, both these testing techniques have their limitations and are nowhere near perfect, therefore, it has become necessary to find better alternative ways to test for the novel coronavirus.
At present, this is the test done on majority of the of the COVID-19 patients, suspected or confirmed.
The sample for performing this test is a swab sample taken from the throat. A blood sample will not work here because there will be a very small amount of the Coronavirus circulating in the blood. Though the antibody presence may be significant, the amount of the virus will be too little to be detected.
The Center for Disease Control recommends a nasopharyngeal swab for the collection of the sample for testing. The lab technician inserts a 6-inch cotton swab inside each of the nostrils and rotates them around for about 15 seconds. The swabs are then sent to the lab for testing purposes.
Other samples that may be collected for testing purposes are swabs from:
- Your mouth and throat
- The middle of your nostrils
- The front of your nostrils
- If you have a cough with expectoration, your cough expectorate may be taken up for testing by the lab.
The swabs taken from the upper respiratory tract are not reliable after the first week of the illness because the virus slips down from the upper respiratory tract lower down into lungs where it replicates at an alarming rate.
Therefore, during the second week of the illness, samples for testing are taken from deep airways inside the lungs collected by a suction catheter or the coughed-up material from deep inside the lungs is used.
RT-PCR test detects the presence of the viral RNA (antigen) in the person and not the presence of the antibodies that the body later produces. This test, therefore, tells you whether the person is infected by the Coronavirus before the antibodies form and before the symptoms appear.
This early detection by the PCR test helps to isolate the person early on and can help identify people he has come in contact with. These people too can then be quarantined.
This early detection is a major advantage, which helps to break the transmission chain and keeps the health authorities on top of what’s happening.
PCR tests are labor-intensive and therefore, present various stages at which human errors may occur from the sampling stage to the receipt of the results.
False-negative results can occur in about 30% of the results. Therefore, a negative result need not fully confirm the absence of the infection.
The PCR test has an 80-85% specificity, which means it has an 80 to 85% chance of correctly detecting the virus. The results are, however, obtained after 2 days.
Serologic testing: Tests to detect antibodies in the blood
The serological test detects the presence of antibodies in the blood. The body makes these antibodies to fight the infection if you are infected. This can happen even before the symptoms present. The antibodies continue to be present in the body even after recovery, which makes you immune to the virus.
Presence of antibodies produced due to earlier infection help to grant immunity against further infections. However, in the case of the novel Coronavirus, it is not yet clear how long or what type of immunity the primary infection will offer to the patient.