Diagnosing Coronavirus SARS-COV-2

Reading time: 4 min

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.

DNA molecule or helix

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).

Molecular tests detect the virus in the sample by amplifying its genetic material to levels that allow detection. Molecular tests are therefore used to confirm active infection, usually within a few days of exposure and around the time when symptoms typically begin. 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 swab

Nasal or pharyngeal smear. The PCR has limitations so the quality of the sample obtained from a nasal or pharyngeal smear is critical.

Rapid or antigen tests detect virus proteins. They are quicker and cheaper than PCR tests, but less accurate. They work best when there is more virus circulating, in other words, when the person is in the most infectious phase of the disease.  

Antibody tests. These are not used to diagnose COVID-19. They are antibody tests that detect whether a person has had an infection in the past, even if they have had no symptoms. A blood sample is used to detect the antibodies generated as the result of an infection. These develop within days or weeks after infection. 

Estudio de contactos

Para evitar la propagación de la epidemia de COVID-19 es clave identificar y diagnosticar de forma rápida los casos positivos para poder aislarlos y comenzar el estudio de contactos estrechos para establecer las medidas oportunas.

Una vez se detecta un caso, comienza la búsqueda de los posibles contactos. Es importante saber que todos estos contactos son personas sanas; son sólo contactos. Son personas que han compartido con la persona con el virus un espacio común (trabajo, domicilio, reunión, viaje).

No todos los contactos tienen el mismo riesgo. Se distingue entre contactos cercanos o estrechos y contactos casuales o no estrechos.

Un contacto estrecho es aquella persona que ha compartido espacio con un caso positivo a menos de 2 metros de distancia, durante más de 15 minutos, sin protección y dentro de las 48 h previas al inicio de los síntomas o de la realización de la prueba diagnóstica (en el caso de que la persona positiva no haya tenido síntomas).

¿Qué debe hacer una persona designada como contacto estrecho?

Una persona que ha sido designada como contacto estrecho de un caso positivo debe realizar un aislamiento en su domicilio durante los 10 días posteriores al contacto. Debe estar localizable, registrar su temperatura dos veces al día y avisar de manera inmediata si aparecen síntomas (tos, fiebre, dificultad respiratoria).

Su equipo de atención primaria se pondrá en contacto con él o ella para programar una prueba diagnóstica (PCR o test de antígenos).

Pasados ​​los 10 días de confinamiento domiciliario, si no hay incidencias, el Servicio de Vigilancia Epidemiológica indicará que ha finalizado la vigilancia y, a partir de aquí, se debe hacer vida normal de nuevo.

No es necesario que las personas consideradas como contactos casuales se queden en aislamiento. Únicamente se les informa de cómo proceder en caso de que tengan síntomas.

El contacto de un contacto no es un contacto. No hay que hacer nada.

Substantiated information by:

Antoni Trilla
Eduard Vieta Pascual
Gema Maria Lledó Ibáñez
Jacobo Sellarés Torres
Josep M. Miró Meda
Josep Maria Peri
Maica Rubinat
Mariona Violan

Published: 12 March 2020
Updated: 12 March 2020

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