Prevalence of SARS-CoV-2 viral RNA in conjunctival swabs of symptomatic COVID-19 patients in the Netherlands

Purpose : The putative presence of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in ocular specimen put ophthalmologists and co-workers at risk. So far, few results are available from small sample size studies. The aim of our study is to evaluate the presence of viral RNA of SARS-CoV-2 in conjunctival swabs of a large cohort coronavirus disease 2019 (COVID-19) patients in the Netherlands. Methods : A total of 243 symptomatic laboratory-confirmed COVID-19 patients were included in this observational multicenter study. Sample collection took place during the 'second wave' of the pandemic (from August to November 2020) in two medical centers in the Netherlands. From a subset of subjects (healthcare workers), consecutive conjunctival samples were available from follow-up visits. Tear/conjunctival samples were obtained by gently sweeping the inferior conjunctival fornices of both eyes with a disposable swab. Samples were analyzed by reverse transcription (RT) PCR for detection of SARS-CoV-2 viral RNA. Results : Viral RNA was detectable in conjunctival swabs from 17 out of 243 (7.0%) COVID19 patients. The mean age of those 17 subjects was 46.7 ± 16.2 years (range 26-80 years) and the male-to-female ratio was 4/13. One subject reported increased tearing as ocular symptom. Conjunctival samples were positive for viral RNA as long as 12 days after disease onset. Cycle threshold (Ct) values for conjunctival swabs (mean 34.5 ± 5.1, range 22.6 42.0) were significantly higher than of nasopharyngeal swabs (mean 16.7 ± 3.6, range 12.1 - 24.3) (p < 0.0001). No correlation (r = -0.10, p = 0.70) between Ct values of conjunctival and nasopharyngeal swabs was observed. The majority of positive conjunctival samples were detected during the first visit, while three subjects became positive during the second visit and one subject during the fourth visit. None of the subjects tested positive in the conjunctival sample more than once. Conclusions : Ocular transmission of SARS-CoV-2 remains a crucial issue that requires vigilance of protecting the ocular surface by wearing protective equipment. Particularly for ophthalmologists, protective measures are warranted during the ophthalmic examination and ocular surgery.