Consensus results

The proposed algorithm is divided into three parts according to time after first contact or time after symptom onset (Fig. 1).
The rRT-PCR is recommended as the primary test in the initial 14 days after symptom onset or close contact. Early sample collection from the upper respiratory tract minimizes the probability of negative rRT-PCR test results (Mallett et al., 2020). If negative, rRT-PCR may be repeated in a different sample, at the discretion of the physician. Antigen detection tests are most likely to perform well in patients with high viral loads in the pre-symptomatic (1–3 days before symptom onset) and early symptomatic phases (within the first 5–7 days of illness)(World Health Organization, 2020). These tests may be used as an alternative in high-prevalence settings or special cases when rRT-PCR tests are unavailable.
The rRT-PCR is the diagnostic test of choice between 8–13 days after initiation of symptoms. If results are negative, rRT-PCR may be repeated. In some cases, antibody assays may be used during this period, but considerations should be taken when the results are negative (false negative tests are still common in this period), or when IgM is positive and IgG is negative, raising the possibility of a false positive test (Deeks et al., 2020).
Fourteen days after symptom onset or close contact, antibody detection assays are recommended as the initial test for the detection of SARS-CoV-2 infection in immunocompetent hosts. In most cases, antibody assays are used to trace contacts or for other epidemiological reasons(Jayamohan et al., 2020), but may be used for individual diagnosis in specific circumstances.
Figure 1. A simplified alternative diagnostic algorithm for SARS-CoV-2 suspected symptomatic patients and confirmed close contacts (asymptomatic)