At the moment, the diagnostic tests have two purposes: the main one is to detect the cases earlier, in order to isolate and treat them, and the second is epidemiological and refers to knowing what the population that has been infected in a community or institution really is. closed. Detecting that some of the individuals have been infected may be an indication that others have the infection.
Another purpose that has been proposed is to find out if a person is immune through the detection of antibodies, but to date there is no certainty that the antibodies are virus blocking agents, nor that the presence of antibodies means that an individual reacts against to a new infection or recurrence. Indicating the latter could therefore generate false security. Therefore, the benefits are focused on treating the sick early and avoiding contagion to other people, therefore, the benefit is individual and collective.
According to the utility that we have previously indicated, we have 2 types of techniques. Some based on the direct detection of the presence of the virus and other techniques based on the indirect detection of having passed the infection by detecting the antibodies that the individual has created after infection.
For the basic objective, which is the early detection of cases, it is carried out through the direct detection of the virus using the already famous RT-PCR technique, which allows amplifying the RNA genetic material of the virus and thus detecting it with high sensitivity and specificity. This makes it possible to ensure that the patient has Coronavirus SARS-CoV19, and requires isolation and treatment based on their symptoms.
The presence of antibodies would cover the second objective that we have set, that is, to detect later that a person has been infected with coronavirus. It should be noted that by differentiating the presence of IgM or IgG with the onset of the patient’s symptoms, we could suggest whether the patient is in a stage of acute evolution or has already remitted.
The combination of the latter techniques with PCR is important, because a negative serology is not indicative that the patient is not infected with coronavirus. In addition, it is known that as the acute infection proceeds, the viral load (or amount of virus) that the patient has decreases, in parallel with an increase in IgM antibodies that are the first to appear after 7 days from the beginning of the symptoms. Therefore, it could be the case that in acute infections in progress of more than 7 days virus is not detected by PCR and if IgM is detected.
Finally, if we only have positive IgG in asymptomatic people, it is highly unlikely that the person still has a virus.
Therefore, we must focus at the present time and in accordance with the indications of the ministry in diagnosing cases of symptomatic patients in which the combination of techniques can add value to avoid the transmission of the disease.
Currently we must follow the instructions of the ministry, and specifically of the Andalusian Health Service, which after the last regulation established a single network of results of COVD-19.
Therefore, if PCR is available, this should be tested in symptomatic patients, and if PCR is not available, rapid tests should be done in patients with symptoms of more than 7 days.
The risks of the tests are their limitations and the interpretations that are made of them and that may lead to an erroneous diagnosis.
Both false positives and false negatives are dangerous.
No test is 100% perfect, but it is possible to avoid the biases that may affect them, such as the taking of samples in the case of the direct detection of viruses carried out in a nasopharyngeal sample. If the sample is taken poorly without reaching the nasopharyngeal cavity, the virus will not be collected in the swab and therefore it will not be detected by PCR, even though it is the best technique. It is very important to have a trained nurse who takes the sample well.
Keep in mind that the virus is an RNA virus that breaks down easily, this can affect the case of sending samples if it is not done under the ideal refrigeration conditions or if processing is delayed.
Another aspect is in the laboratory process itself, which consists of several phases. It is essential to work in the best security conditions requiring a prepared laboratory and specialized personnel. The RNA extraction phase is very important, a bad extraction will give false negatives, false positive processing errors, etc. To obtain the highest sensitivity in our laboratory, we use 3 genetic targets of SARS-CoV2, some with short fragments, which avoids the effect that the virus may have in its continuous variations or mutations that occur in it.
Therefore, there are many factors that can influence the quality of the results
Another essential aspect is knowing the patient’s clinical situation, in order to be able to indicate the performance of serological tests. Therefore, they must be prescribed by a doctor.
A patient with symptoms and positive should be in the hands of their doctor. The doctor must be the one guiding the test, therefore, it is the doctor who must give you the appropriate indications for its treatment and isolation.
At its facilities, HC Internacional has the technical means, trained personnel and a level 2 biosafety laboratory to detect the virus using the RT-PCR reference technique.
Only a few private hospitals have this technique due to the technical requirements it requires and the specialized personnel necessary to do it.
This gives us an added and differential value, allowing to have the results on the same day, both for hospitalized patients and patients who go on an outpatient basis.
Furthermore, we ensure complete traceability of the process by being supervised by ourselves.
The contact with the radiology service that allows completing the diagnoses, as well as having a hospital pharmacy, allows to guide the treatments, which are directly supervised by the doctor who requests the tests.
Therefore, we must highlight the global team to act against COVID-19 in HC, without forgetting the nursing team that plays a primary role from taking samples to caring for patients.
Dr. Marco Antonio Sempere Alcocer
Microbiology and Parasitology Specialist
April 21, 2020
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