Lack of financing. Furthermore, antigen tests were incorporated into contact detection, so the study lost interest.

Stopping the SARS-CoV2 spread is essential to control the pandemic cause by this virus.

A great effort is being made to carry out surveillance, case detection and contact control protocols in order to detect and isolate those contagious subjects.

Since both symptomatic and asymptomatic subjects can be contagious, a surveillance system based on the presence of symptoms is not enough, requiring to perform diagnostic tests in a large number of subjects, such as asymptomatic contacts or high-prevalence populations, and repeatedly. Moreover, the speed in obtaining results is crucial in order not to delay the isolations of positive subjects.

The polymerase chain reaction (PCR) is an expensive test which requires specialized equipment and personnel with a delay in results of 24-48 hours. In addition, its high sensitivity can mean that subjects without infective capacity have a positive result.

In contrast, antigen detection tests (ADTs) are cheap and easy to perform, having a result in few minutes. They have shown high sensitivity and specificity in symptomatic subjects, specially in the first week of symptoms when the viral load is high. This could be very useful for the study of asymptomatic contacts to detect those with potential contagiousness quick, easily and cheaply. However, there is no evidence to support the use of ADTs in this group of subjects.

For this reason, the investigators propose to carry out a study to compare the diagnostic efficacy of ADTs versus PCR in the group of subjects considered to be close contacts of SARS-Cov2 positive patients in the health area of Cáceres.

Inclusion Criteria:

• Subjects considered close contacts of COVID-19 patients according to the definition of the Ministry of Health of Spain at the time of inclusion.

Exclusion Criteria:

• Subjects who do not obtain their informed consent for the study.
• Symptomatic subject at the time of inclusion.

All subjects considered close contacts of COVID-19 patients according to the definition of the Ministry of Health of Spain in the health area of Cáceres

Additional related documents such as study protocol, statistical analysis plan and informed consent form will be available upon request from the project principal investigator.

(Dr. Juan Fernando Masa Jiménez). De-identified patients´data can be requested by researchers for use in independent scientific research and will provided following review and approval of the research proposal (including statistical analysis plan) and completion of a data sharing agreement with the Project Publications Committee. Investigator Data requests can be made anytime from 1 to 2 years after the publication of this trial. Requests should be sent to the corresponding author (Dr. Juan Fernando Masa Jiménez- fmasa@separ.es)