Buccal swabs underpowered to detect COVID-19 in kids

While detection of SARS-CoV-2 is possible, buccal swabs appear to show substantially lower viral loads than nasopharyngeal samples, according to a new Singapore study.

“[W]e confirm the detection of SARS-CoV-2 from buccal specimens of children with coronavirus disease 2019 (COVID-19),” researchers said. The lower viral loads, however, make buccal swabs inferior to nasopharyngeal testing.

Eleven children with laboratory-confirmed COVID-19 were enrolled. Six (54.5 percent) were asymptomatic while the remaining five showed symptoms, though disease course remained mild throughout. Asymptomatic patients were older, but not significantly so. [J Pediatric Infect Dis Soc 2020;doi:10.1093/jpids/piaa068.]

In majority (81.8 percent; n=9) of the participants, at least one buccal sample tested positive for SARS-CoV-2.

One patient whose buccal specimen came back negative was asymptomatic and had nasopharyngeal cycle threshold (Ct) values of 33.0 and 30.0 on day 1 and 2, respectively, of diagnosis. The other was a symptomatic participant with Ct values of 26.9 and 36.2 on days 2 and 3 of illness, respectively.

In those with positive buccal samples, Ct values showed an average difference of 10.7 relative to nasopharyngeal swabs. This difference was statistically significant (p<0.001), indicating much lower viral loads detected in buccal specimens.

Buccal swab sensitivity relative to nasopharyngeal samples ranged from 25 percent to 71.4 percent on different days during the first week of illness.

Moreover, by day 8 of diagnosis, SARS-CoV-2 was undetectable in buccal swabs even if nasopharyngeal testing returned positive results. No significant correlation between buccal and nasopharyngeal Ct values was reported.

“[I]f the virus could be detected in saliva, this suggests a potential route of viral transmission in children, especially in infants who tend to drool and place objects in their mouths,” the researchers said. “It is important to understand the viral shedding pattern in buccal specimens of children in order to predict the routes of viral transmission.”

“The detection of virus in buccal specimens from children suggests a high possibility that similar to adults, SARS-CoV-2 is present and potentially transmissible via the saliva of children,” they added. The low viral load, on the other hand, suggests that this is not a major route of transmission.

In the present study, participants were enrolled through the KK Women’s and Children’s Hospital in Singapore. SARS-CoV-2 diagnoses were confirmed through the real-time reverse transcription polymerase chain reaction assays performed on nasopharyngeal swabs. Buccal swabs were collected data from the bilateral mucosa.

“Our study is limited by a small sample size of 11 children with COVID-19. No further buccal specimens were collected after 3 April 2020, and hence, we could not extend our observations beyond that time,” the researchers said. “Buccal swabs for SARS-CoV-2 are not good as screening specimens for COVID-19 in children.”