COVID-19 Contact Study by Antigen Detection Test

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.