Results
The median age of the 10 patients (6 men and 4 women) with COVID-19 was
44.95 years (range, 29–79 years). Of the 10 patients, 4 had
hypertension, 2 were taking antihypertensive medications, 1 was
receiving an angiotensin-converting enzyme inhibitor, and 1 was
receiving an angiotensin II receptor blocker. On the basis of their
supplemental oxygen use, the patients were divided into the mild and
severe groups. Of the 4 patients in the severe group, 2 were intubated
and were on mechanical ventilators, including 1 patient supported with a
high-flow nasal cannula via nasal prongs and 1 with nasal
prongs only. Four patients in the severe group received
lopinavir/ritonavir. In the mild group, 1 elderly patient with pneumonia
received lopinavir/ritonavir and 1 with consistently low Ct values
received hydroxychloroquine. The remaining patients in the mild group
did not receive antiviral medications (Table 1).
Among the patients with COVID-19 observed in this study, the Ct values
of the upper respiratory tract specimens were low during the early
stages after symptom onset but gradually increased over time in both the
severe and mild groups. Moreover, patients in the severe group had lower
Ct values than those in the mild group did. The Ct values of theRdRP and E genes on day 6 after symptom onset were
significantly lower in the severe group than in the mild group (p
< 0.05). The values increased at a slower rate in the severe
group than those in the mild group did during the first 3–6 days after
symptom onset. Moreover, virus shedding lasted longer in the severe
group (Figure 1).
The viral load in the lower respiratory tract specimens remained
undetectable in the mild group 7 days after symptom onset. However,
virus shedding persisted for more than 3 weeks in the severe group
(Figure 2; see Appendix Figure 1 and Appendix Figure 2).
The positive rate of the SARS-CoV-2
on the PCR test—performed with a nasopharyngeal swab targeting theRdRP gene during the admission period—was 48.3% when the
cut-off value was 35 and 74.1% when the cut-off value was 38. When theE gene was targeted, the positive rate of the SARS-CoV-2 on the
PCR test performed with the nasopharyngeal swab was confirmed to be
55.2% when the cut-off value was 35 and 74.1% when the cut-off value
was 38. The positive rate of the SARS-CoV-2 on the PCR test—performed
with a sputum specimen targeting the RdRP gene—was 43.2% when
the cut-off value was 35 and 50.0% when the cut-off value was 38. When
the E gene was targeted, the positive rate of the SARS-CoV-2 on
the PCR test performed with the sputum specimen was confirmed to be
46.3% when the cut-off value was 35 and 50.0% when the cut-off value
was 38.
During hospitalization, Ct values for both the mild and severe group
tended to be lower at symptom onset and tended to increase with time. In
particular, 3 of 6 patients showed positive results on PCR even before
symptom onset, and 2 of them had the lowest Ct values.
Of the 3 patients, one had a Ct value of 16.19 (nasopharyngeal swab,E gene) 2 days before symptom onset and the other had a Ct value
of 13.75 (sputum specimen, E gene) 1 day before symptom onset.
The Ct value of the test results during the asymptomatic phase of these
3 patients (patient E, patient G, and patient J) was included in the
result of day 0 after symptom onset, as shown in Figure 3.
The mean ± standard error of the mean (SEM) Ct value obtained using the
nasopharyngeal swab during the incubation period was 22.20 ± 4.0 when
the RdRP gene was targeted and 21.28 ± 3.88 when the Egene was targeted. The mean Ct value obtained using the sputum specimen
was 22.46 ± 6.02 when the RdRP gene was targeted and 23.33 ± 7.18
when the E gene was targeted during the incubation period. The
lowest Ct value was observed on day 3 after symptom onset, and the mean
Ct value obtained using the nasopharyngeal swab was 21.49 ± 1.91 when
the RdRP gene was targeted and 21.19 ± 1.94 when the Egene was targeted. The mean Ct value obtained using the sputum specimen
was 19.76 ± 1.61 when the RdRP gene was targeted and 18.88 ± 1.01
when the E gene was targeted (Figure 3; Table 2).
The chest radiograph scores were higher in the severe group than in the
mild group and were significantly different on days 9, 12, and 15 after
the onset of symptoms. Moreover, the chest radiograph scores in the
severe group were the highest at approximately 3 weeks after symptom
onset (Figure 4; see Appendix Figure 3).