The most common symptoms are fever, a dry cough, and tiredness. Other less frequent symptoms that affect some patients are aches and pains, nasal congestion, headache, conjunctivitis, a sore throat, diarrhea, loss of taste or smell, and skin rashes or color changes on the fingers or toes.
The number of children and adolescents affected by COVID-19 is still unknown, although it is estimated to range from 1-4%; systematic studies with more patients are necessary. This is a key question that the Kids Corona platform intends to answer. You can find more detailed information on this topic on our home page.
There are two types of tests to detect COVID-19 available: viral tests (which indicate whether you are currently infected) and antibody tests (which indicate whether you currently are or have previously been infected).
Viral tests usually analyze samples from the respiratory system (e.g. from inside the nose or pharynx, taken with long swabs) to detect the presence of the SARS-CoV-2 virus, which is responsible for COVID-19, by using PCR or tests called “rapid antigenic tests”.
Antibody tests analyze blood samples using the ELISA technique or also by using “rapid serological tests” to look for antibodies against the SARS-CoV-2 virus. Antibodies are proteins produced by our immune cells against infection. They help us fight it (when we are still infected) and protect us from contracting it again (once we have already recovered from the infection). When these tests are performed on blood samples, they are called serological tests.
The “Polymerase Chain Reaction” test, or PCR, is considered the most reliable test. It is a direct diagnostic test of COVID-19 that allows us to detect the genetic material (RNA) of the virus in samples collected. In this way, we can know if we are currently infected.
The test is usually done by taking a sample of respiratory secretions with a long swab from the inside of the patient’s nose or pharynx, and it can also be done on saliva. This allows us to know if the virus is found in these samples. Samples can also be taken from other places, such as from feces, but are not usually used for diagnosis but rather for complementary research studies.
Although a positive result confirms the presence of the virus, a negative result from a patient considered very likely to have COVID-19 should be confirmed with a new test. The disadvantage of this test is that it must be performed in a laboratory and the results take longer to arrive, but it has a higher sensitivity.
Serological testing is an indirect diagnostic method based on a blood sample that, instead of detecting the virus that causes COVID-19 (called SARS-CoV-2), detects the production of antibodies (our body’s defenses) by our immune system.
The antibodies detected by the serological test are IgM (immunoglobulin M) and IgG (immunoglobulin G), which bind to the virus to deactivate or eliminate it. The production of IgM type antibodies usually coincides with the onset of symptoms and does not usually last more than two weeks. The secretion of IgG-type antibodies occurs between days 5 and 7 from the onset of symptoms. These remain for a longer time and are indicative of immunity.
Therefore, if IgM-type antibodies are detected, it means that the disease has been contracted and the risk of being contagious is higher. By the time that no IgM but only IgG antibodies are detected, we know that the infection has passed and protective antibodies have been developed, but the person is no longer contagious. It is important to say that it is still unknown whether the production of antibodies confers protection against a new SARS CoV-2 infection or for how long.
The ELISA test, or “Enzyme-Linked Immunosorbent Assay”, is usually performed on a blood sample and allows the detection of antibodies, which are produced when the patient has been infected and has developed an immune response to the virus. For more information on tests with blood samples, see the question “What is a serological test and what are the differences between IgM and IgG?”.
Compared with the ELISA test, “rapid tests” are less reliable but, as the name suggests, they are faster and can be performed anywhere a suspected case is detected.
“Rapid tests” can be performed on blood or respiratory mucous samples and have the advantage, as the name implies, of providing a fast result without the need for specialized equipment, although they are not highly reliable. They work in a similar way to a pregnancy test.
“Rapid tests” performed on a blood sample are capable of detecting antibodies produced by the body when encountering the virus and therefore can indicate who has already had COVID-19. For more information on tests with blood samples, see the question “What is a serological test and what are the differences between IgM and IgG?”.
“Rapid tests” performed on respiratory samples can detect virus proteins. If the result is positive, it would indicate that you currently have the infection. A negative result from a patient with high suspicion of COVID-19 should be confirmed with a new test.
Isolation of 2 weeks is recommended for people with symptoms, people who have received a positive PCR test and people who have been in contact with infected people or to places of risk. It is always advisable to accompany this isolation with a diagnosis by PCR to confirm the presence of the virus.