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The diagnosis of any disease depends on the history as well as the set of symptoms and signs presented by the patient, taking into account the epidemiological situation and a lot of other data interpreted by the medical team. There is no single diagnostic test, but there are several possibilities. After that, certain complementary examinations and laboratory tests are then considered and evaluated.
When dealing with infectious diseases it is very important to have tests that quickly identify which microorganism is involved. This allows decisions to be made on the most appropriate treatment and management.
Polymerase chain reaction (PCR). SARS-CoV-2 can be identified using the PCR test carried out in a microbiology lab. This is considered the reference standard for molecular diagnosis. The test has a good level of sensitivity (i.e., the probability that a person with COVID-19 gives a positive test result; does not give false negatives), and good specificity (i.e., the probability that a person without COVID-19 has a negative test result; does not give false positives).
The test may be negative in the early stages of infection, and in these cases may provide a false sense of security. The test that detects the RNA of the virus may not reflect the presence of viable virus (with the ability to infect). At the end of the disease, the result may be that the patient is fine, they are cured, but the PCR still returns a positive result.
Nasal or pharyngeal smear. The PCR has limitations so the quality of the sample obtained from a nasal or pharyngeal smear is critical.
At this time, the test is performed only in duly accredited laboratories and in those investigative cases that meet the epidemiological and clinical criteria set out in the protocol. It is not performed on contacts while these remain asymptomatic.
If the current number of cases increases significantly, the test would be reserved only for the highest risk patients and the most serious cases that may require hospital admission. When there is an epidemic situation, the resources must be streamlined and rationalised.