Saliva specimen complements anal swab in assessing patients with COVID-19 for discharge from hospital

Figures & data

Figure 1. Sample profiles in each specimen type. Number of samples and viral RNA concentration are compared among the three specimen types. A. Total number of samples and proportion recorded in different periods after hospitalization. The percentage of samples collected during the first 7 days was higher in O/N swab than anal swab and saliva, while after the second 7 days the percentage was lower in O/N swab. B. Viral levels were compared among anal swab, O/N swab and saliva. Percentage of samples with higher viral level (Ct≤35), low viral level (35 < Ct≤40) and negative results (40 < Ct) are presented for the first 7 days, the second 7 days and the period after the second 7 days of hospitalization.

Table 1. Demographic characteristics of the patients.

Total	60
Gender – no. (%)
Male	41 (68)
Female	19 (32)
Age – no. (%)
10–19	4 (7)
20–29	12 (20)
30–39	24 (40)
40–49	14 (23)
50–59	5 (8)
60–69	1 (2)
Average	35.1 (range: 19–61)
Classification of clinical severity* – no.(%)
Mild	47 (78)
Moderate	13 (22)

*Clinical severity of the symptoms was classified according to the eighth edition of the guideline for diagnosis and treatment of SARS-CoV-2 issued by the National Health Commission of the People's Republic of China.

Figure 2. Detection profiles according to specimen type. Sensitivity and trend of viral RNA concentration are compared among anal swab, O/N swab and saliva. A. Number of patients detected (positive), undetected (negative) and with excluded results (X) in each specimen type. B. Number of patients with positive result in each specimen type each day after hospitalization. C. Viral RNA concentration in all detected patients by each specimen each day after the first positive result of each patient. D. The kinetics of anti-COVID-19 IgM and IgG in serum after onset of symptoms. RLU: the detected signals relative light units.

Table 2. Profiles of RT-PCR results using different specimens.

Profiles of results			Number of patients	Percentage in total (%)
Saliva	Oropharyngeal swab	Anal swab
+	+	+	37	71.15
+	–	–	1	1.92
+	+	–	0	0
+	–	+	1	1.92
–	+	+	4	7.69
–	+	–	2	3.85
–	–	+	2	3.85
–	–	–	5	9.62

Table 3. Difference and concordance of saliva and O/N swab with anal swab as reference.

		Anal swab		McNemar's test	Kappa test
		Positive	Negative
Saliva	Positive	38	1	P = 0.125	Kappa value = 0.588
	Negative	6	7		P < 0.001
O/N swab	Positive	41	2	P = 0.999	Kappa value = 0.649
	Negative	3	6		P < 0.001

Figure 3. Analyses of Conversion Days comparing pairs of specimens. Conversion Days was calculated as days from hospitalization to the last positive viral RNA result. The Pearson correlation coefficient was used to measure the strength of the correlation between conversion days of each two specimens. Correlation of Conversion Days between anal swab and saliva(A), O/N swab and saliva (B), and O/N swab and anal swab (C). D. Comparison of Conversion Days between each pair of saliva, O/N swab and anal swab (Paired t test).

Figure 4. Analyses of Conversion Days of CT scanning and hs-CRP. A. Correlation of Conversion Days between CT scanning and hs-CRP. B. Comparison of Conversion Days between CT scanning and hs-CRP (Paired t test). C. Correlation of Conversion Days between CT scanning and RT-PCR with each of the three specimen types. D. Correlation of Conversion Days between hs-CRP and RT-PCR with each of the three specimen types. The Pearson correlation coefficient was used to measure the strength of the correlation.

Figure 5. Impact of symptoms on conversion days of viral RNA and other clinical test. Patients were grouped according to their severity of symptoms (A), respiratory symptoms (B) and digestive symptoms (C) respectively. Conversion Days were compared. Difference between each two subgroup were determined by Student's t test.