Ocular surface manifestations and SARS-CoV-2 RNA detection in conjunctival swabs of patients hospitalized for COVID-19 pneumonia

Dear Editor

Coronavirus disease 2019 (COVID-19) can appear with a wide range of clinical manifestations including respiratory, cardiovascular, gastrointestinal, neurological, dermatological, and ocular involvement.

The SARS-CoV-2 virus can affect all segments of the eye: conjunctivitis, uveitis, retinitis, and optic nerve damage have all been described [1]. The most frequent ocular symptom is conjunctivitis [2] and it has been suggested that disease transmission can occur via this route.

Evidence has been established that SARS-CoV-2 may infect human ocular surfaces including the epithelium of the cornea, limbus, and conjunctiva as they contain angiotensin-converting enzyme 2 and transmembrane protease serine 2 receptors on their surfaces [3]. Previous studies have reported a wide variability in SARS-CoV-2 RNA detection rates in tear fluids.

We describe the results of a a study whose aims were to investigate the presence of SARS-CoV-2 in the tear fluid of hospitalized COVID-19 patients, to assess the relationships between ocular symptoms and the presence of SARS-CoV-2 in the tear fluid, and the association of systemic and ophthalmic clinical features.

Fifty-eight COVID-19 hospitalized patients (74% male, median age of 56 years) were included in this prospective study in the first 10 days after admission, between September 2020 and May 2021. All patients had a pathognomonic chest CT scan. All included individuals provided written informed consent to participate in the study. The study protocol was approved by the Saint-Pierre University Hospital ethics committee (CE/20-06-05).

Twenty-eight percent of the patients had neurological symptoms, including headaches (19%), asthenia, confusion, and dizziness, while 28% had digestive symptoms such as vomiting and diarrhoea. Nineteen percent of the patients experienced anosmia or ageusia. On ocular surface symptom questionnaire, 13 patients (22%) presented with tearing (69.23%), redness (53.85%), burning (38%), or itching (15.38%). All but one reported that the symptoms started at the beginning of SARS-CoV-2 infection (92.31%). Results of the ocular examinations are reported in Table 1 .

Table 1.

Frequency of ocular abnormalities at examination.

Conjunctival hyperaemia	Chemosis	Discharge	Tearing	Eyelid oedema
grade 1: 5% grade 2: 2%	0%	0%	5%	0%

A conjunctival swab was then performed. Tears and cellular debris were collected from one randomly chosen eye with a sterile synthetic fibre swab into the lower fornix without topical anaesthesia. For the last five patients, both eyes were tested with two separate swabs. The swab was immersed in a viral transport medium and stored at −80 °C before being tested by reverse transcriptase and polymerase chain reaction (RT-PCR) assays, processed with either the AltoStar® SARS-CoV-2 RT-PCR Ki, or the Alinity m SARS-CoV-2 assay. The cycle thresholds (Ct) were evaluated, and the result was considered as negative if Ct ≥ 40. Only 2 (3.5%) of the conjunctival swabs RT-PCR were positive, while 54 (93.1%) of the nasopharyngeal swabs were positive.

Logistic regression highlighted a significant correlation between the presence of ocular symptoms and neurological symptoms (p= 0.021). No significant statistical difference was found between ocular symptomatic and asymptomatic patients, and between patients with positive and negative conjunctival swabs.

This study has shown that, despite severe COVID-19 infection, usually associated with high viral load, the rate of positive RT-PCR for SARS-CoV-2 in tears was very low. However, a significant proportion of patients suffered from ocular symptoms that seem unrelated to the presence of the virus in tears.

The respiratory tract is probably not the only route of transmission for COVID-19. Faecal-oral transmission has also been described, with positive RT-PCR obtained from the stool of hospitalized patients. Viral transmission through the ocular surface has been also described, from direct inoculation, or migration of the virus from the upper respiratory tract [4]. The presence of the virus in tears does not necessarily mean that the ocular surface is the site of transmission [5]. Gijs et al. [6] performed conjunctival swabs in both eyes in 243 symptomatic COVID-19 patients. Of the whole population, 7% were positive, but there was a difference in terms of positivity between patients (2.75%) and healthcare workers (10.4%). Viral load, measured by Ct, was also lower in tears than in nasopharyngeal swabs. A 13% positivity rate for SARS-CoV-2 RNA on the ocular surface was described in 487 asymptomatic/non-severe SARS-CoV-2 infections [7], but Rokhol et al. [8] did not report any positive conjunctival swabs in a series of 1145 asymptomatic patients.

The variability of these prevalence rates may be related to variations in the timing of conjunctival swab collection relative to the onset of symptoms. Gijs et al. [6] effectively highlighted that, when performing consecutive swabs in positive patients, only the swab performed during the first week of infection was positive. In the present study, both positive cases were newly admitted and had a shorter time interval from onset to sampling.

Cycle threshold (Ct) values also varied from one study to another. This may explain a higher rate of positive swabs. In our study, Ct >40 was considered negative, which is above the threshold applied in some other studies. Of note, different methods can have different Ct values for the same sample [9].

The collection, transport, and storage of the samples could also affect virus stability, and, thus, the results. Most of the swabs in this study had been frozen for a long time before analysis because laboratories were overwhelmed with ongoing acute cases during that period. The two positive conjunctival swabs were stored for 8 months before analysis. The fact that the virus was collected and stored at −80 °C probably did not affect the positivity of the swabs in our study as the cold chain was maintained.

Regarding ocular symptoms, the prevalence in COVID-19 patients is highly variable from one series to another. A systematic review of 38 studies (8219 patients) reported an overall prevalence of 7.6% [10]. We observed a somewhat higher prevalence (22%), maybe explained by a systemic inflammatory state caused by the virus.

An association between ocular symptoms and the presence of neurological symptoms was also observed, as in the series from Rousseau et al. [7], where headache tended to be more frequent in patients with ocular symptoms (83% vs 54%, P=0.06). Once again, these non-specific symptoms might be related to systemic inflammation and release of pro-inflammatory substances such as cytokines. Another possibility could be the activation of the trigeminovascular system through local or systemic dysregulated inflammatory mediators.

In this study, ocular symptoms were not related to a positive conjunctival swab nor to disease severity. This suggests that tears can be infected without any ocular symptoms.

We can conclude that a small proportion of patients hospitalized for COVID pneumonia had high SARS-CoV-2 viral loads in their tear fluid. The eyes of COVID-19 patients should be manipulated with caution, independently of the presence or lack of ocular symptoms. Ocular symptoms are frequent in hospitalized COVID-19 patients and are not associated with the presence of SARS-CoV-2 in tears.

The authors would like to acknowledge the contribution of a medical writer, Sandy Field, PhD, for English language editing and formatting of this manuscript.