Poor oral hygiene could affect accuracy of SARS-CoV-2 tests
TOKYO, Japan: A study conducted at a hospital in Tokyo has found that poor oral hygiene could lead to prolonged viral shedding in patients with COVID-19. In the study, it was observed that patients with inadequate oral health regimes returned positive results in polymerase chain reaction (PCR) tests for the virus long after their clinical recovery, leading the researchers to believe that oral hygiene could affect the accuracy of testing for the virus.
The researchers evaluated the course of treatment of eight COVID-19 patients who were admitted to the Department of Neurology at Tokyo Metropolitan Neurological Hospital between 30 April and 14 May. The patients had passed the acute phase of the disease, but were admitted to the dedicated medical facility for infectious diseases owing to persistent positive PCR test results for SARS-CoV-2.
The study found that, among the patients, the viral shedding period—the period during which the virus was still detectable after clinical recovery—ranged from one to 40 days. The average viral shedding period was found to be 15.1 days, but for two patients, Patient 1 and Patient 2, it continued for 53.0 days and 44.0 days, respectively. For Patients 3–8, two consecutive negative PCR test results were confirmed within 18 days of clinical recovery.
The researchers sought to establish why Patients 1 and 2 continued to test positive for the extended period. They noted that Patients 3–8 had kept up their personal hygiene routines, which included regular toothbrushing, while hospitalised in isolation in private rooms in the hospital. Patients 1 and 2, however, who had mental and/or psychiatric disorders, had not voluntarily brushed their teeth while hospitalised. After being instructed by the researchers to practise regular toothbrushing and gargling, the PCR tests of Patients 1 and 2 returned a negative result within four to nine days.
“Patient 1 had schizophrenia and was unable to voluntarily keep herself clean during isolated hospitalised life,” the study reads. “She brushed her teeth for the first time on the 18th day of hospitalisation, but after that, she did not brush her teeth at all. Her virus shedding period reached 46 days, with consistently positive PCR test results. We speculated that her inappropriate oral care might have caused the persistence of PCR test positivity. In collaboration with the nurse, we repeatedly encouraged Patient 1 to brush her teeth and gargle. Two days after the start of this instruction, on the 49th day after the patient’s onset of symptoms, the patient’s PCR test result was negative for the first time.”
Patient 2, who had the underlying diseases of dissociative disorder and mild mental retardation, returned a negative PCR test result 26 days after being admitted to the medical facility; however, the viral shedding period reached 43 days before two consecutive negative PCR test results could be obtained. “At that time, we found that Patient 2 rarely brushed her teeth. Since then, we repeatedly instructed her to brush her teeth. With four days of intensive toothbrushing with only water, Patient 2 had two consecutive negative PCR test results on Days 44 and 47, so she was discharged,” the researchers wrote.
They acknowledged that the low number of patients who were followed in the study made it difficult to draw statistical conclusions from the research, but noted that it was significant that the two patients with poor oral health regimes had displayed significantly longer than average viral shedding periods. “In such prolonged viral shedding cases, non-infectious viral nucleic acid may accumulate in an uncleaned oral cavity and may continue to be detected by PCR. We propose toothbrushing and gargling to remove accumulated non-infectious viral nucleic acid, leading to consistently negative PCR test results and thus avoiding unnecessarily long hospital stays,” the researchers concluded.
The study, titled “Effects of oral care on prolonged viral shedding in coronavirus disease 2019 (COVID-19)”, was published online on 24 July 2020 in Special Care in Dentistry, ahead of inclusion in an issue.