Testing for the SARS coronavirus by using a patients tear drops

Jun 22 2004

Scientists have shown that they can test for the SARS coronavirus by using a patients tear drops.

A team of ophthalmologists, virologists and infectious disease specialists from the National University Hospital, Singapore, Tan Tock Seng Hospital and Singapore General Hospital made their discovery working with teardrops taken from 36 patients in April last year. All of the 36 were suspected of having SARS.

Eight patients were eventually confirmed as having contracted the SARS and the actual virus was found in the teardrops of three of them. The detection method was based upon similar technology used to detect the virus in blood and stool samples.

Scientists believe that the timing of the tear drop sampling is crucial in obtaining valid results. The samples from three patients who tested positive were taken within nine days after fever started, the teardrops of the other patients who tested negative were collected after 9 days.

The research leader, Loon Seng Chee said: 'We were surprised to find that tests on one patient's tears picked up the virus at an early stage, while tests of her blood and other fluids could not. So this could become important in diagnosing SARS in the future.'

Getting a suspected patient's tears would be more convenient than getting a blood or stool sample as it is painless, can be taken at any time and more tears can be collected easily, added the associate consultant ophthalmologist at The Eye Institute, which oversees the eye departments of TTSH and NUH.

He explained that in general, in the early stages of an infectious disease, a sufferer's tears, nasal discharge, blood and stool would be chock-full of the virus. But as the disease waned, the virus would not be present in as large quantities.

Another researcher who worked on the project, Dr Stephen Teoh, said the study also suggests the possibility of the virus being spread by tears, like the ones which cause conjunctivitis and flu.

Initial SARS symptoms are flu-like, in that there can be any or all of the following symptoms: fever, myalgia, lethargy, gastrointestinal symptoms, cough, sore throat and other non-specific symptoms. The only symptom that is common to all patients appears to be a fever above 38 degrees Celsius. Later in the disease, susceptible patients will develop shortness of breath.

Symptoms usually appear 2-10 days (up to 13 days have been reported) after infection - in most cases symptoms appear around 2-3 days after infection. In about 10-20% of the cases, symptoms are so severe that patients have to be put on a ventilator.