Low risk of COVID-19 spreading through tears
By Denise Baez
The risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission through tears is low, according to a study published in the journal Ophthalmology.
Ivan Seah, MD, National University Hospital, Singapore, and colleagues collected tear samples from 17 patients with laboratory-confirmed coronavirus disease 2019 (COVID-19) using Schirmer’s test strip at varying time-points between day 3 and day 20 after the initial development of symptoms. Samples from both eyes were taken and analysed separately.
Nasopharyngeal swabs were collected routinely for clinical monitoring of patient’s condition while tear samples were collected purely for research purposes. On some days, both tears and nasopharyngeal swabs were collected at the same time. These samples were delivered to different labs for processing.
Of the 17 patients, none presented with ocular symptoms. However, 1 patient developed conjunctival injection and chemosis during the stay in the hospital. Most (82.35%) patients presented with upper respiratory tract symptoms including cough, rhinorrhoea, and sore throat.
A total of 64 samples were taken over the study period, with 12, 28 and 24 samples taken from first, second and third week of initial symptoms respectively. All were tested negative for the SARS-CoV-2 on viral isolation and quantitative reverse transcription polymerase chain reaction (RT-PCR).
There was no evidence of SARS-CoV-2 shedding in tears through the course of the disease. All tear samples tested negative even when nasopharyngeal swabs continued to test positive. Patients who presented with upper respiratory symptoms did not demonstrate any viral shedding in tears.
Viral load detected in nasal and throat swabs were elevated for a period of approximately 2 weeks from the onset of COVID-19 symptoms.
Only 1 patient developed ocular symptoms during the disease course and no evidence of SARS-CoV-2 could be found in the tear samples.
“This suggests that transmission through tears regardless of the phase of infection is likely to be low,” the authors wrote. “However, further definitive mechanistic studies are required. Future studies involving more patients with ocular symptoms should also be considered. Future studies should also consider the association between serum viral load and viral shedding in tears.
The authors acknowledged several limitations to their study, the first being that nasopharyngeal swabs and tear samples were analysed in different laboratories utilising 2 different assays. Tear samples were incubated with Vero-E6 cells for 4 days prior to obtaining the RNA for RT-PCR. After 4 days, cells were observed for the presence of cytopathic effect (CPE). If SARS-CoV-2 existed in the samples, CPE would have been observed even in a false negative RT-PCR result. The researchers did not observe CPE or a positive RT-PCR result, confirming the low likelihood of SARS-CoV-2 being found in the tear samples. Other limitations included the sampling of tears rather than conjunctival tissue, which was avoided to reduce patient distress, and the small sample size of the study due to the logistical limitations of the outbreak response.