A new study has found that nasopharyngeal swabs, taken from inside the nostril, were more effective at detecting COVID-19 than saliva tests or swabs from just inside the nostril or under the tongue.The study also found that detection rates were lower in asymptomatic patients, confirming the rationale for shorter isolation regimens.For the study, researchers at Cornell University (Ithaca, NY, USA), used different patient samples: nasopharyngeal swabs, anterior nasal swabs (in front of the nostril), saliva, and sublingual swabs (under the tongue).The researchers also collected samples from symptomatic, asymptomatic, and post-symptomatic individuals (those who had recovered from the disease) to better understand the efficiency of testing in these populations.When they compared the different types of samples, the researchers found that nasopharyngeal samples provided the best detection rate, from 92% to 100%.This is probably because the virus replicates in the nasal concha, the tissue structures at the top of the nose.Detection rates for anterior nostrils and saliva samples were slightly lower, 92% to 96% for symptomatic patients.This detection rate was lower when the samples came from asymptomatic patients (75% to 92%).Detection of SARS-CoV-2 from sublingual samples was much worse, with detection rates of only 40% to 60% in samples from symptomatic patients and 25% to 42% in samples from asymptomatic patients.Detection rates in symptomatic, asymptomatic, and post-symptomatic patients were fairly intuitive, with detection being strongest in symptomatic patients, ranging from 92% to 100%, depending on the test used.In all tests, the virus was slightly more difficult to detect in asymptomatic patients, with a rate of 75 to 96%.Once symptoms resolved in post-symptomatic patients, detection became much more difficult.The team also investigated infectivity – the level of infectious viral particles excreted in each of the sample types and from different categories of patients.As predicted, most of the infectious samples came from symptomatic patients, while less than a third of the samples collected from asymptomatic patients were infectious.The researchers were unable to isolate any infectious virus from samples from post-symptomatic patients.These new data provide healthcare professionals with practical guidance."The study addressed the very important issue of identifying a sample type that would allow reliable detection of the virus, without significantly compromising detection sensitivity," said Dr. Diego Diel, associate professor in the Department of Population Medicine and Diagnostic Sciences and director of the virology laboratory at the Animal Health Diagnostic Center, who was the lead author of the study."We were surprised by the relatively short period in which infectious virus could be detected."Related Links: Cornell University