Disease diagnosis and application analysis of molecularly imprinted polymers (MIPs) in saliva detection

Abstract Background The initial cases of novel coronavirus (2019-nCoV)–infected pneumonia (NCIP) occurred in Wuhan, Hubei Province, China, in December 2019 and January 2020. We analyzed data on the first 425 confirmed cases in Wuhan to determine the epidemiologic characteristics of NCIP. Methods We collected information on demographic characteristics, exposure history, and illness timelines of laboratory-confirmed cases of NCIP that had been reported by January 22, 2020. We described characteristics of the cases and estimated the key epidemiologic time-delay distributions. In the early period of exponential growth, we estimated the epidemic doubling time and the basic reproductive number. Results Among the first 425 patients with confirmed NCIP, the median age was 59 years and 56% were male. The majority of cases (55%) with onset before January 1, 2020, were linked to the Huanan Seafood Wholesale Market, as compared with 8.6% of the subsequent cases. The mean incubation period was 5.2 days (95% confidence interval [CI], 4.1 to 7.0), with the 95th percentile of the distribution at 12.5 days. In its early stages, the epidemic doubled in size every 7.4 days. With a mean serial interval of 7.5 days (95% CI, 5.3 to 19), the basic reproductive number was estimated to be 2.2 (95% CI, 1.4 to 3.9). Conclusions On the basis of this information, there is evidence that human-to-human transmission has occurred among close contacts since the middle of December 2019. Considerable efforts to reduce transmission will be required to control outbreaks if similar dynamics apply elsewhere. Measures to prevent or reduce transmission should be implemented in populations at risk. (Funded by the Ministry of Science and Technology of China and others.)

Summary Background Coronavirus disease 2019 (COVID-19) causes severe community and nosocomial outbreaks. Comprehensive data for serial respiratory viral load and serum antibody responses from patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are not yet available. Nasopharyngeal and throat swabs are usually obtained for serial viral load monitoring of respiratory infections but gathering these specimens can cause discomfort for patients and put health-care workers at risk. We aimed to ascertain the serial respiratory viral load of SARS-CoV-2 in posterior oropharyngeal (deep throat) saliva samples from patients with COVID-19, and serum antibody responses. Methods We did a cohort study at two hospitals in Hong Kong. We included patients with laboratory-confirmed COVID-19. We obtained samples of blood, urine, posterior oropharyngeal saliva, and rectal swabs. Serial viral load was ascertained by reverse transcriptase quantitative PCR (RT-qPCR). Antibody levels against the SARS-CoV-2 internal nucleoprotein (NP) and surface spike protein receptor binding domain (RBD) were measured using EIA. Whole-genome sequencing was done to identify possible mutations arising during infection. Findings Between Jan 22, 2020, and Feb 12, 2020, 30 patients were screened for inclusion, of whom 23 were included (median age 62 years [range 37–75]). The median viral load in posterior oropharyngeal saliva or other respiratory specimens at presentation was 5·2 log10 copies per mL (IQR 4·1–7·0). Salivary viral load was highest during the first week after symptom onset and subsequently declined with time (slope −0·15, 95% CI −0·19 to −0·11; R 2=0·71). In one patient, viral RNA was detected 25 days after symptom onset. Older age was correlated with higher viral load (Spearman's ρ=0·48, 95% CI 0·074–0·75; p=0·020). For 16 patients with serum samples available 14 days or longer after symptom onset, rates of seropositivity were 94% for anti-NP IgG (n=15), 88% for anti-NP IgM (n=14), 100% for anti-RBD IgG (n=16), and 94% for anti-RBD IgM (n=15). Anti-SARS-CoV-2-NP or anti-SARS-CoV-2-RBD IgG levels correlated with virus neutralisation titre (R 2>0·9). No genome mutations were detected on serial samples. Interpretation Posterior oropharyngeal saliva samples are a non-invasive specimen more acceptable to patients and health-care workers. Unlike severe acute respiratory syndrome, patients with COVID-19 had the highest viral load near presentation, which could account for the fast-spreading nature of this epidemic. This finding emphasises the importance of stringent infection control and early use of potent antiviral agents, alone or in combination, for high-risk individuals. Serological assay can complement RT-qPCR for diagnosis. Funding Richard and Carol Yu, May Tam Mak Mei Yin, The Shaw Foundation Hong Kong, Michael Tong, Marina Lee, Government Consultancy Service, and Sanming Project of Medicine.

To the Editor: Rapid and accurate diagnostic tests are essential for controlling the ongoing Covid-19 pandemic. Although the current standard involves testing of nasopharyngeal swab specimens by quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) to detect SARS-CoV-2, saliva specimens may be an alternative diagnostic sample. 1-4 Rigorous evaluation is needed to determine how saliva specimens compare with nasopharyngeal swab specimens with respect to sensitivity in detection of SARS-CoV-2 during the course of infection. A total of 70 inpatients with Covid-19 provided written informed consent to participate in our study (see the Methods section in Supplementary Appendix 1, available with the full text of this letter at NEJM.org). After Covid-19 was confirmed with a positive nasopharyngeal swab specimen at hospital admission, we obtained additional samples from the patients during hospitalization. We tested saliva specimens collected by the patients themselves and nasopharyngeal swabs collected from the patients at the same time point by health care workers. Using primer sequences from the Centers for Disease Control and Prevention, we detected more SARS-CoV-2 RNA copies in the saliva specimens (mean log copies per milliliter, 5.58; 95% confidence interval [CI], 5.09 to 6.07) than in the nasopharyngeal swab specimens (mean log copies per milliliter, 4.93; 95% CI, 4.53 to 5.33) (Figure 1A, and Fig. S1 in Supplementary Appendix 1). In addition, a higher percentage of saliva samples than nasopharyngeal swab samples were positive up to 10 days after the Covid-19 diagnosis (Figure 1B). At 1 to 5 days after diagnosis, 81% (95% CI, 71 to 96) of the saliva samples were positive, as compared with 71% (95% CI, 67 to 94) of the nasopharyngeal swab specimens. These findings suggest that saliva specimens and nasopharyngeal swab specimens have at least similar sensitivity in the detection of SARS-CoV-2 during the course of hospitalization. Because the results of testing of nasopharyngeal swab specimens to detect SARS-CoV-2 may vary with repeated sampling in individual patients, 5 we evaluated viral detection in matched samples over time. The level of SARS-CoV-2 RNA decreased after symptom onset in both saliva specimens (estimated slope, −0.11; 95% credible interval, −0.15 to −0.06) (Figure 1C) and nasopharyngeal swab specimens (estimated slope, −0.09; 95% credible interval, −0.13 to −0.05) (Figure 1D). In three instances, a negative nasopharyngeal swab specimen was followed by a positive swab at the next collection of a specimen (Figure 1D); this phenomenon occurred only once with the saliva specimens (Figure 1C). During the clinical course, we observed less variation in levels of SARS-CoV-2 RNA in the saliva specimens (standard deviation, 0.98 virus RNA copies per milliliter; 95% credible interval, 0.08 to 1.98) than in the nasopharyngeal swab specimens (standard deviation, 2.01 virus RNA copies per milliliter; 95% credible interval, 1.29 to 2.70) (see Supplementary Appendix 1). Recent studies have shown that SARS-CoV-2 can be detected in the saliva of asymptomatic persons and outpatients. 1-3 We therefore screened 495 asymptomatic health care workers who provided written informed consent to participate in our prospective study, and we used RT-qPCR to test both saliva and nasopharyngeal samples obtained from these persons. We detected SARS-CoV-2 RNA in saliva specimens obtained from 13 persons who did not report any symptoms at or before the time of sample collection. Of these 13 health care workers, 9 had collected matched nasopharyngeal swab specimens by themselves on the same day, and 7 of these specimens tested negative (Fig. S2). The diagnosis in the 13 health care workers with positive saliva specimens was later confirmed in diagnostic testing of additional nasopharyngeal samples by a CLIA (Clinical Laboratory Improvement Amendments of 1988)–certified laboratory. Variation in nasopharyngeal sampling may be an explanation for false negative results, so monitoring an internal control for proper sample collection may provide an alternative evaluation technique. In specimens collected from inpatients by health care workers, we found greater variation in human RNase P cycle threshold (Ct) values in nasopharyngeal swab specimens (standard deviation, 2.89 Ct; 95% CI, 26.53 to 27.69) than in saliva specimens (standard deviation, 2.49 Ct; 95% CI, 23.35 to 24.35). When health care workers collected their own specimens, we also found greater variation in RNase P Ct values in nasopharyngeal swab specimens (standard deviation, 2.26 Ct; 95% CI, 28.39 to 28.56) than in saliva specimens (standard deviation , 1.65 Ct; 95% CI, 24.14 to 24.26) (Fig. S3). Collection of saliva samples by patients themselves negates the need for direct interaction between health care workers and patients. This interaction is a source of major testing bottlenecks and presents a risk of nosocomial infection. Collection of saliva samples by patients themselves also alleviates demands for supplies of swabs and personal protective equipment. Given the growing need for testing, our findings provide support for the potential of saliva specimens in the diagnosis of SARS-CoV-2 infection.