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)