Discussion
In this study, we found a low prevalence of SARS-CoV-2 among patients presenting at the emergency outpatient ophthalmological healthcare facility at the county hospital, indicating low exposure of SARS-CoV-2. Additionally, we demonstrated low seroprevalence of SARS-CoV-2 IgG-antibodies among hospital staff at the ophthalmological ward.
The county of Västmanland is situated in the greater Stockholm area and has been hit hard by SARS-CoV-2. The incidence of COVID-19 as per 6 July 2020 was 873 per 100 000 inhabitants in Västmanland and 902 per 100 000 inhabitants in Stockholm, respectively.18 Nevertheless, few patients in need for emergency ophthalmological healthcare were infected with SARS-CoV-2, suggesting good adherence to the recommendations by the healthcare authorities of social distancing in all situations and avoidance of any contacts in case of fever or respiratory tract symptoms.18
In case patients attending the clinic presented at the reception desk with symptoms suggestive of COVID-19, they were immediately asked to return home and the appointment at the eye clinic was postponed. At the time of the study, precautionary measures included physical distancing during all aspects of the appointment at the clinic, also in the waiting areas. All slit lamps had been supplied with protective plastic shields. Frequent use of alcohol disinfectants on all equipment, with which the patients had been in contact during the appointment, was applied. Facial masks or visors were not in use at this time neither by healthcare professionals nor by patients as according to recommendations by the healthcare authorities.
Conjunctivitis was diagnosed in 7% of patients in our study. None of these patients were positive for SARS-CoV-2 in either the conjunctival or throat swab, suggesting that the cause of conjunctivitis was other than infection with SARS-CoV-2 in our patients although this cannot be completely ruled out. In five Italian patients with lengthy conjunctivitis without improvement for several days, PCR on nasopharyngeal swabs was positive for SARS-CoV-2.7 Conjunctivitis remained the only symptom of COVID-19 in these patients and no patient developed fever or respiratory symptoms.7 Additionally, in a retrospective review of patients, who had previously been hospitalised with COVID-19, 6 out of 56 individuals (11%) reported ocular symptoms such as sore eyes, itching, foreign body sensation, tearing, redness, dry eyes, eye secretions and floaters up to 7 days before the onset of fever or respiratory symptoms.6 Further, in the study from the Hubei province in China in hospitalised patients with at least moderately severe COVID-19, conjunctivitis was reported in almost a third of the patients.2 SARS-CoV-2 was detected on RT-PCR in both conjunctival and nasopharyngeal swabs in two out of 12 patients with ocular symptoms, indicating that virus can be discharged in conjunctiva and tears in critically ill patients.2 Taken together, the findings suggest that high-level attention should be applied when meeting patients with symptoms of conjunctivitis in the times of the pandemic.
One patient was found to be positive for SARS-CoV-2 in the throat swab. This patient presented with a sudden reduction in visual acuity, which turned out to be caused by a preretinal haemorrhage in the macular area. No risk factors for preretinal haemorrhage were identified in this patient. Retinal vascular events have been reported in conjunction with other systemic viral infections.19 Further, in a case series of patients with severe COVID-19, 10 out of 18 patients had retinal abnormalities such as flame-shaped haemorrhages or cotton-wool spots, suggesting involvement of retinal vasculature.20 Although our patient was not critically ill, it cannot be ruled out that the haemorrhage was related to the SARS-CoV-2 infection. Contact tracing after the positive PCR-test was obtained did not reveal any transmission to hospital staff.
The seroprevalence of SARS-CoV-2 IgG-antibodies was low, 4%, among hospital staff at the department of ophthalmology. A much higher seroprevalence of 19% among healthcare staff was reported from a hospital in Stockholm11 whereas prevalence of SARS-CoV-2 IgG antibodies in hospital staff at a tertiary centre in Belgium was 6.4%.12 The findings indicate large variations in exposure and seroconversion among hospital staff also between relatively closely situated hospitals. The low seroprevalence at our department likely mirrors the low prevalence of SARS-CoV-2 infection in our patients and is in line with good adherence to recommendations by the healthcare authorities also by the hospital staff. It is also important to bear in mind the possibility of ‘seroreversion’. Such loss of seropositivity over time was found in 12.2% of initially seropositive participants in a study from Tokyo, Japan, by means of repeated testing over 3–5 weeks.21 Our questionnaire showed that a majority of the staff reported symptoms which could be associated with COVID-19 and had subsequently stayed home from work.
The findings indicate that the general precautions taken at the ophthalmological ward including social distancing, plastic shields on the slit lamps, hand disinfection and careful use of alcohol disinfectant on all contact surfaces were sufficient to prevent transmission.
One strength of our study is the cross-sectional design with simultaneous PCR testing of patients and serological testing of the staff at the department. Another strength is a high willingness to participate in the study, and only very few patients and none of the staff declined to participate.
Even though almost all consecutive patients were included during the study period, one weakness was the small sample size, which has to be taken into account when interpreting the results. The absence of a positive RT-PCR test from the conjunctiva and throat in our study participants may be attributed to chance and not represent the true prevalence. A larger sample of patients would have yielded a more accurate estimate of the true prevalence. On the other hand, the patients demonstrated variability of diagnoses and were considered a representative selection of patients at the department. It should also be emphasised that the study population consisted of individuals at the outpatient facility; the patients were allowed to attend the clinic only after screening questions suggestive of COVID-19 were negative, reducing the risk of COVID-19 among participants.
The serological tests used in the study were able to correctly recognise the two individuals from the staff that were previously known to have been COVID-19 PCR positive. The combined use of two different and highly specific serological tests provides a high positive predictive value, even in a low prevalence population such as ours.
No previous asymptomatic COVID-19 infections were identified but cannot be entirely ruled out, as a recent study suggests a rapid loss of antibodies among patients with asymptomatic COVID-19.22 Also, the potential role of a T-cell mediated immunologic response to COVID-19 may lead to an underestimation of prior exposure to the virus. However, the vast majority of COVID-19 symptomatic patients develop antibodies23 and a potential T-cell response is unlikely to significantly alter the findings of this study.
In conclusion, a low prevalence of SARS-CoV-2 among patients and low prevalence of seropositivity for SARS-CoV-2 among ophthalmological staff were demonstrated, indicating low exposure and low risk for contracting SARS-CoV-2 at the department of ophthalmology at present. Protection against airborne spreading and close contact with infected persons, the main transmission routes, continues to be highly relevant.24 Since the situation is rapidly evolving, a repeated measurement in patients and staff is planned to closely follow the development.
