Research conducted by scientists at the University of São Paulo (USP) concluded that the Covid-19 virus can be detected in tears through swab tests, a flexible rod with cotton at the tip used to collect material for examinations.
Analyzing samples of patients hospitalized at the Hospital das Clínicas in Bauru (SP) with a diagnosis of the disease confirmed with conventional methods, the researchers detected SARS-CoV-2 on the ocular surface using this type of test in 18.2% of cases . The result indicates an alternative to the nasal and oral swab, which causes nose and throat discomfort, and signals the need for protective measures for healthcare workers as, although low, there is a risk of transmission of the virus through tears.
Furthermore, the combination of two factors — more comorbidities and higher mortality rate — among patients with a positive tear test suggests that viral detection may aid in disease prognosis.
The findings were published in an article in the Journal of Clinical Medicine.
“At the beginning of the research, we thought of looking for an easy diagnostic method, with the collection of material without much inconvenience for the patients. The nasal swab, in addition to causing discomfort, is not always used correctly. For people with a deviated septum, for example, it can be a problem. We thought the tear would be easier to do, more tolerable. We managed to demonstrate that it is a path. A limitation of this study is that we do not know whether the amount of tears collected affects positivity or not,” says the article’s corresponding author, Professor Luiz Fernando Manzoni Lourençone, of the Bauru Faculty of Dentistry and Rehabilitation Hospital of Craniofacial Anomalies, both from USP.
According to the researcher, it can be inferred that the probability of detecting the virus in tear samples is higher in patients with a high viral load, which can lead to disseminated viremia from various body fluids.
The work received the support of FAPESP through an initiation science grant awarded to Luís Expedito Sabage, an undergraduate student, under the supervision of Lourençone.
Of the 61 hospitalized patients, samples were analyzed of 33 of whom diagnosed with Covid-19 and another 14 without the virus, obtained during the first half of 2021, when the main variants circulating in the State of São Paulo were gamma and delta. .
Scientists used two ways to collect tears: the conjunctival swab and Schirmer strips (examination to assess whether the eye produces enough tears). The evaluations were carried out between July and November of the same year.
Of the total, SARS-CoV-2 was detected in 18.2% of swab samples and 12.1% of Schirmer strip samples. On the other hand, as expected, none of the patients negative for COVID-19 in nasopharyngeal swab tests had a positive tear sample.
To assess comorbidities, the group adopted the Charlson Comorbidity Index (CCI), composed of 20 factors and developed as a way to standardize and adjust risk indicators, discriminating a patient’s prognosis in terms of mortality over the period up to a year.
According to the research, people whose tears tested positive for SARS-CoV-2 had lower CHF than the rest (indicating a higher likelihood of dying in ten years) and higher mortality rates.
Regardless of the COVID-19 diagnosis, most people had low tear production and eye discomfort, indicating the need for artificial tears during their hospitalization.
In addition to data on demographic, clinical and ocular symptoms, the scientists worked with reverse transcription polymerase chain reaction (RT-qPCR) analyses. The method requires the extraction of genetic material; a process of transcription of RNA into DNA and, finally, the multiplication of DNA. Considered the gold standard for the diagnosis of Covid-19 and widely used in various laboratories around the world, the test is able to detect the presence of even a single copy of the genetic material of the virus in the sample.
Unlike previous studies, where viral genes (N and RdRp) were not considered in RT-qPCR analyses, in this case the research identified different parts of the virus, resulting in a better detection rate.
In July 2021, the result of the work of a team from the Faculty of Medical Sciences of the University of Campinas (FCM-Unicamp) who accompanied 83 patients admitted to the Hospital de Clínicas of the city, of which 8.43% had samples tears or the ocular surface positive for disease.
“When we started, in early 2021, we didn’t have the technology to cross-reference certain types of data, moving from basic science to clinical practice. Meanwhile, Sabage interned at the Byers Eye Institute, in the Stanford University Department of Ophthalmology. [Estados Unidos], a reference in studies of complex ocular fluids. With the available technology, it was possible to perform several matings and verify the presence of SARS-CoV-2 in the tears of our samples. Partnering with another team brought results to our campus and opened a new line of research,” adds Lourençone at Agência FAPESP.
The internship at Stanford was supported by FAPESP.
Now, the group of researchers has started a new line focused on detecting diseases through tests and examinations related to the eyes. The goal is to work with other types of viruses than SARS-CoV-2.
“There are other viruses that still need to be studied in Brazil. We intend to dedicate ourselves to finding solutions and improving the quality of life of patients. We will also analyze other viral conditions that become systemic,” says the professor.
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