Clinical characteristics and viral load dynamics of COVID-19 in a mildly or moderately symptomatic outpatient sample

Abstract

Background: Studies of outpatients with mild or moderate COVID-19 are uncommon. We studied: 1) association of symptoms with reverse transcriptase polymerase chain reaction (RT-PCR) test results; and 2) association of initial RT-PCR cycle threshold (Ct) in relation to duration of RT-PCR positivity in outpatients with mild or moderate COVID-19.

Methods: This was a cohort study of outpatients with confirmed COVID-19 and at least one symptom. Participants had repeat nasopharyngeal swabs and symptom checklists every 3-5 days until two consecutive RT-PCR tests were negative. RT-PCR tests were used to assess viral load. Antibody tests for COVID-19 were performed at 2 weeks, 4 weeks, and 8 weeks after symptom onset.

Results: Twenty-five patients (nine females) were enrolled, ranging in age from 19-58 (median age 28 years). All patients reported at least one symptom, with a median of six symptoms per patient. Symptoms persisted for 6-67 days (median duration 18 days). In all 25 patients, blood samples collected a median of 13 days after symptom onset were positive for SARS-CoV-2 antibodies in 15 (60%). After a median of 28 days following symptom onset, 23/23 patients with available samples tested positive for antibodies. The longest duration of positive RT-PCR test was 49 days from first positive PCR test (Mean = 27.4, SD = 12.5, Median = 24). Initial Ct was significantly associated with longer duration (β = -1.3, SE = 0.3, p<0.01 per 1 cycle higher) of RT-PCR positivity.

Conclusions: In mildly or moderately ill COVID-19 outpatients, RT-PCT tests remained positive for as long as 49 days and test positivity and symptom duration correlated with initial viral load.

Fig 1. Viral load evolution for each patient.

Cycle count, measured in samples collected every 3–5 days from first positive RT-PCR test to first of two negative RT-PCR tests, in patients with complete data.

Fig 2. Duration of positive RT-PCR test for SARS-CoV-2 according to initial cycle threshold (Ct).

Duration of positive RT-PCR test was negatively correlated with initial cycle threshold (Ct). Longest duration of positive test in this study was 49 days from symptom onset.

Fig 3. Duration of positive RT-PCR test for SARS-CoV-2 according to number of symptoms.

Duration of positive RT-PCR test was positively associated with number of symptoms. Patients with more symptoms had a positive RT-PCR test significantly longer than patients with fewer symptoms.