Conjunctival Swabs Not Sensitive Enough to Detect COVID-19

Doctor Testing Biological Specimen
The presence of coronavirus RNA in conjunctiva does highlight tears as a possible mode of disease transmission, the report suggests.

Conjunctival swabs should not be used for the detection of COVID-19, as they have especially low sensitivity; however, a small percentage of patients may test positive for COVID-19 with conjunctival swabs, highlighting tears as a possibility mode of disease transmission, according to study results published in Clinical Ophthalmology. 

Previous studies have found that SARS-CoV-2 can be transferred via mucous membranes, including the conjunctiva, which reflects in reported cases of ophthalmologists contracting the virus during normal diagnosis and treatment; however, the detection of the virus within tears is still often debated. 

A team of investigators from Saudi Arabia conducted a cross-sectional study to the presence of viral ribonucleic acid (RNA) within the ocular surface in patients who tested positive for COVID-19 via nasopharyngeal swabs to determine whether the conjunctival swabs were effective and sensitive in detecting COVID-19

Of the 164 patients (164 eyes) included in the analysis, only 4.9% tested positive for COVID-19 via conjunctival swab. Of the cohort, 29.9% had fever, 28.7% had shortness of breath, 20.1% had a cough, and 12.2% had red eye. 

A total of 18.9% of patients reported a history of traveling and 73.2% of patients reporting having contact with someone who tested positive for COVID-19, and traveling was found to be a risk factor for a positive conjunctival swab test (P =.016). 

Compared with patients who did not have diabetes mellitus or hypertension, there was a significant association between a positive conjunctival swab test and diabetes (P =.049) or hypertension (P =.002). 

The researchers found the sensitivity of conjunctival swab to be 4.8%. “It is possible the viruses appear for short period in the eye, which may need specific and precise collection time,” according to the report. 

“The high correlation between [diabetes mellitus] and the positive presence of the virus in conjunctival swabs suggested that patients with [diabetes mellitus] are at risk of contracting COVID-19 infections in comparison with other diseases,” the research says. 


Hadrawi M, Malak M, Almahmoudi F, et al. Testing the sensitivity of conjunctival swabs from confirmed COVID-19 patients. Clin Ophthalmol. 2021;15:2489-2496. doi:10.2147/OPTH.S313721