In the three months since 12 March, 2003, when the World Health Organization (WHO) issued a global alert on severe acute respiratory syndrome (SARS), the Health Protection Agency (HPA) has reported on eight individuals who fitted the case definition for probable SARS to the WHO. Four of these have subsequently been found to be due to other causes, leaving four probable cases, one of which has been confirmed on the basis of the detection of antibodies to the SARS corona virus (SARS CoV).
The probable cases represent only a small proportion of the cases considered by the HPA. Over 400 cases of illness in United Kingdom (UK) residents have been reported to the HPA’s Communicable Disease Surveillance Centre (CDSC) for consideration as potential SARS cases. CDSC has been collating information on these referrals and the WHO SARS collaborating laboratory in the Enteric, Respiratory, and Neurological Viruses Laboratory, in, Colindale, London, and has been testing a large number of clinical specimens.
In Scotland, SCIEH reported 17 cases to the UK SARS Team of whom 13 were registered as suspect cases. Two of these were subsequently de-registered owing to the detection of other causes.
As a result of this work, two UK residents who were unwell with a respiratory illness while abroad have been found to have antibodies to the SARS CoV. Both are now fully recovered and the authorities in the country where they were ill have been informed and have followed up their close contacts. On the basis of their illness, their travel history and the laboratory results, these two people have now been retrospectively classified as probable SARS cases. The cases have been reported to the WHO, but they will not be counted as UK SARS cases as they acquired their infection and were ill overseas.
A further three UK residents have been found to have antibodies to the SARS CoV. Two of the three cases had signs and symptoms that are less than are required to meet the suspect or probable case definition, and all three had only limited potential for exposure to SARS. All three have recovered from their illness and investigations by local health care workers have found no evidence of clinical illness in their close contacts in the UK. These cases probably represent mild illness as a result of SARS CoV infection and indeed such cases have been reported elsewhere1. It is, however, difficult to be certain of the implications of these findings until more information accumulates on the clinical spectrum of illness caused by SARS CoV and the characteristics of the antibody test in populations with a low prevalence of infection. Further laboratory testing is being carried out on these cases.
Data from the global epidemic shows that nearly all cases of SARS can be attributed to close contact with other people who have SARS. The extent to which people with a mild illness caused by the SARS CoV can transmit infection remains undetermined, although this is currently considered to be much less important than transmission from cases that are severely unwell. Transmission has not been reported from people without symptoms2. Data presented by virologists and epidemiologists from Hong Kong and Singapore on viral genome detection and infectiousness at a recent global SARS epidemiology conference in Geneva was consistent with patients being considerably more infectious in the second week of their illness and when they had more severe disease. The current WHO case definition, which focuses on more severe disease, is proving to be an effective tool in controlling SARS and will not be altered for the time being. Nevertheless, there is a need to develop definitions that accommodate people for whom SARS CoV causes only a mild illness.
It is probable that further cases will be identified of mild illness in people whose opportunity for exposure to SARS has been very limited, but in whom there is laboratory evidence of exposure to the SARS CoV. Dialogue will continue with WHO about the appropriate classification of such cases.
- Booth CM, Matukas LM, Tomlinson GA, Rachlis AR, Rose DB, Dwosh HA, et al. Clinical features and short-term outcomes of 144 patients with SARS in the Greater Toronto Area. JAMA 2003; 289 (21). Available at: http://jama.ama-assn.org/cgi/content/full/289/21/2801
- NIAID. SARS: developing a research response. Presentation to national institute of health: National Instittute of Alergy and Infectious Diseases, 30 May 2003. [online] [cited 12 June 2003]. Available at: http://www.niaid.nih.gov/SARS/meetings/05_30_03/PDF/stohr.pdf
[Article first appeared in: CDR Weekly, 12 June 2003. http://www.phls.org.uk/publications/cdr/PDFfiles/2003/cdr2403.pdf]