The Covid-19 pandemic has shaped 2020 and continues to reverberate today, with the effects of infections, virus variants, and the unprecedented global effort to address prevention and treatment. Italy, among the first countries to manage infections and lockdowns, has demonstrated impressive healthcare organizational efforts and leading research teams, united to quickly find a way to address the epidemic.
Words like " Covid test " and " swab " have entered everyday language, and a huge segment of the population of all ages has already had to take at least one. Swabs, in fact, are the first and most effective tool for preventing and analyzing the disease from the first symptoms, and their contribution to tracking the pandemic has been extremely significant.
Science and medicine have, in a short time, developed specific forms of Covid test, capable of tracking the different methods and timing of possible contagion, with appropriate differences that can be useful based on the use that is made of them.
But not everyone is yet clear about these particularities and which test to request based on symptoms or cases of possible contagion.
Among the COVID tests that will be examined, some are already well-known and widespread. They can be requested at the laboratories of the Medi Multi-Specialist Center in Castellammare di Stabia . We asked them to explain their main features and differences, how they work, and their efficacy levels . It's important to clarify some tests, as they are still rarely used.
Covid molecular swab
When we think of a molecular test , the first thing that comes to mind is a swab. This type of test is now widespread and has become one of the symbols of this pandemic period: it is the most widespread and safe COVID test for detecting the presence of the virus in the body.
The swab is inserted into the nasal passages of the person undergoing the test and is designed to identify the virus's genetic material in the nasopharyngeal mucosa. If this material is recognized by the reverse transcription polymerase chain reaction (RPR) molecular tests , it means the person is positive for the SARS-CoV-2 virus.
It is certainly a reliable tool, but all in all slow (from hours to a couple of days are needed for the results), without considering the exposure to the risk of contagion of the operator who carries out the swab itself.
Molecular testing is useful for confirming any rapid swab tests or for assessing the status of quarantined individuals (both if they begin to show symptoms and if it's necessary to confirm their recovery). The test can be performed at clinical laboratories, and costs may vary from region to region.
Covid Antigen Test
The molecular test therefore searches for the virus's constituent genetic material. The antigen test , on the other hand, identifies specific viral proteins (antigens). The method used to recognize the proteins is the same as the molecular test: a nasopharyngeal swab is used (similar to a cotton swab with a longer shaft), but the test provides a quicker response in these cases.
We're talking about a wait of just fifteen minutes, but the test's reliability, on the other hand, is lower than that of a molecular swab: it is therefore recommended to confirm an antigen test (now commonly referred to as a " rapid swab ") with a second molecular test, to avoid the risk of false negatives.
Given the rapidity of the test, however, the antigen test is recommended when necessary for school or work (due to its rapidity) or, again, in the case of mild symptoms if there has been no close contact with positive subjects (symptomatic or asymptomatic).
Covid Serological Test
Unlike the two previous tests, the serological test does not look for genetic or antigenic components of the virus, but for antibodies produced by the body in response to the coronavirus. If present, they indicate the body's contact with the virus itself, but they cannot indicate a current infection. Indeed, once infection has occurred, the body takes several days to mobilize the appropriate antibodies, which remain circulating in the blood even long after the virus has been expelled.
In this sense, serological tests have no diagnostic value: being negative to a serological test could mean – in some cases, for example – having an ongoing infection and not having yet produced the right antibodies (the virus could still be in the incubation phase); on the contrary, a high antibody count does not help to recognize when you have come into contact with the virus. However, it is a very useful test for studying the epidemic itself, and for analyzing its progress in more or less large communities.
There are three types of serological tests, the costs of which – at clinical analysis laboratories – vary from region to region:
- Rapid serological test or qualitative: the analysis of a single drop of blood is sufficient to verify – in just twenty minutes – whether the body has produced antibodies against the coronavirus.
- Quantitative serological test: it is based on a venous blood sample; the blood is analyzed to trace IgG and IgM antibodies, that is, the first to appear in case of infection. The reliability is around 98%. If the IgM immunoglobulins are positive, you will be dealing with a recent infection. Otherwise (positivity of the IgG antibodies and IgM negativity), the infection has now passed; in this last case we can speak of a potential immunization of the subject.
- Quantitative spike test: this is a serological test aimed at finding active antibodies against the S protein (Spike) of the SARS-cov-2 virus. This latter test is particularly suitable for verifying the immunization of the subject following recovery from a coronavirus infection or completion of the vaccination cycle against the coronavirus.
Again, the test is based on the analysis of venous blood, which is subjected to chemiluminescence (a test with a specificity of 99,6% and sensitivity of 100%). This is a test that is worth carrying out two weeks after completing the vaccination cycle or three weeks after the Covid-19 infection: in both cases, it will be possible to verify the presence in the blood of antibodies capable of recognising and attacking the Spike protein that the coronavirus uses to attack cells: once this protein is neutralized, the virus will have no way of infecting the host organism.
Being therefore more targeted and specific than the two previous serological tests, it Spike test it proves more suitable for monitoring one's immune response to the virus over time, following recovery or vaccination.
Covid saliva tests
Recently, tests similar to molecular and antigen tests have been developed, which, however, do not depend on a nasopharyngeal swab but are based on the analysis of a saliva sample. This is therefore a less invasive test than the classic swab or venous sampling and, for this reason, could prove to be a fundamental tool for rapid screening of entire communities. However, there are some data to keep in mind.
The molecular saliva test , in fact, has a waiting time of about an hour and is only extremely suitable in certain circumstances: for example, to confirm the validity of a positive antigen test. The saliva antigen test has a contraindication: it requires a sample to be taken at a specialized laboratory; therefore, it is not suitable for rapid screening.
Covid Prevention and Testing
The strategy for preventing and containing the spread of the Covid -19 pandemic is based on the so-called 3 Ts : testing, tracing, and treating. Thus, the first step (testing the population) is crucial to continuing the process of identifying and treating any positive cases.
Over time, different types of tests have been developed and others are still being developed, to ensure ever greater speed in recognizing positive subjects, so as to nip any potential outbreak in the bud. For this reason, tests are confirmed as the main tool for preventing the spread of Covid infection.
