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Severe acute respiratory syndrome (SARS) was first recognised in Guangdong Province in China and later in Hong Kong in March 2003.1 Within a matter of weeks, the outbreak has evolved to become a global health threat and almost 30 countries have been afflicted with the novel coronavirus strain (SARS-CoV).2 SARS is a highly contagious potentially lethal disease. The main route of transmission is by respiratory droplets, though the virus has also been isolated in stool and in urine. Tears, being one of the body fluids, may potentially harbour the coronavirus. The presence of viruses in these body fluids may affect our precaution practices and sites of sampling for diagnostic tests.
A prospective interventional case series study was conducted on the identification of the SARS-CoV virus in tear secretions and conjunctival cells of patients with confirmed SARS. Approval was obtained from the ethics committee of the Chinese University of Hong Kong. Consecutive patients with probable SARS in the Prince of Wales Hospital, Hong Kong, during the epidemic period from April to May 2003 were recruited. Other than the routine samples of nasopharyngeal, mouthwash and stool, tear swab and conjunctival scraping were taken randomly from one eye of all recruited patients.
The tear swab was taken by putting a sterile cottonwool stick into the deep lower fornix of each patient’s eye after a single drop of topical anaesthetic agent (1% amethocaine eye drops) was applied. Conjunctival scraping was performed at the lower palpebral conjunctiva with a bent tip of a sterile 23 gauge needle. All ocular samples were collected by a single ophthalmologist with personal protective equipment recommended by the infection control unit of the hospital. Particular care was taken not to contaminate the samples.
The samples were analysed by virus culture and RT-PCR. The SARS-CoV specific primers COR-1 (sense) 5′ CAC CGT TTC TAC AGG TTA GCT AAC GA 3′ and COR-2 (antisense) 5′ AAA TGT TTA CGC AGG TAA GCG TAA AA 3′ were used to detect the presence of SARS-CoV RNA.3 All the patients were further categorised as confirmed SARS with a seroconversion or fourfold increase in antibody titre. The antibody against coronavirus was detected by indirect immunofluorescent technique based on Vero cells infected with SARS-CoV isolated from a patient with SARS.3
A total of 20 probable SARS patients were recruited and 17 were later confirmed with paired convalescent sera. Among the confirmed cases, the mean age was 40.5 (SD 8.8) years and 12 (70.6%) were female. They were recruited during the first (n = 6, 35.3%), second (n = 8, 47.1%), and third (n = 3, 17.6%) weeks of their diseases. Five (29.4%) of the 17 patients were positive for SARS-CoV by PCR with the samples from nasopharynx or stool (table 1). In all tear and conjunctival scraping samples, no SARS-CoV virus could be detected by RT-PCR or isolated by viral culture. Apart from two patients having mild and self limiting conjunctival bleeding after scrapings, no other ophthalmic complication was reported.
The routes of transmission of SARS other than respiratory droplets and stool are still enigmatic. In fact, tears have been reported by the World Health Organization to be one of the body fluids that might convey the novel SARS coronavirus, though the infectivity or clinical significance is not known.4
The negative findings of SARS-CoV viral genetic material or viable virus in the tear secretion or conjunctival cells of patients with serologically confirmed SARS may have several interpretations. Firstly, RT-PCR testing or viral culture is known to be very specific but lacks sensitivity. Peiris and colleagues reported that only 22 of 44 (50.0%) nasopharyngeal aspirate samples and 10 of 18 (55.6%) faecal samples from patients confirmed with SARS had coronavirus genetic material detected by RT-PCR.5 So negative test results can be false negative and do not exclude the presence of the virus. Sensitivity can be increased if multiple specimens are tested. Secondly, it is possible that the virus and its genetic material were only present for a brief period of the disease, and the samples were not collected at the right time. Thirdly, the virus might not be present in tears at all.
The limitations of this study are the relatively small sample size and only the fact that one sample of tear swab and conjunctival scraping were taken from each patient. We cannot totally exclude the presence of virus in the tear secretion, but it is clear that conjunctival swabs and conjunctival scrapings are not useful samples for confirming or excluding the diagnosis.
Financial and proprietary interest: Nil.
Financial support: Supported by the Action for Vision Eye Foundation, Hong Kong.
Conflict of interest: Nil.