Where are we with SARS?
Health
with Dr Walter Chin
Stabroek News
May 11, 2003
Up to the present, at least 29 countries have reported cases of severe acute respiratory syndrome (SARS). Globally, over 7,000 people have been infected, and at least 506 people have died. The outbreak seems to have peaked in Canada, Hong Kong, Singapore and Vietnam. The World Health Organization has warned that the SARS outbreak may still not have reached its peak. While the disease has been eliminated in Vietnam and was on its way down in Canada, in other countries it still appears to be on the rise.
Because there is no diagnostic test available for SARS, health professionals refer to 'suspect' or 'probable' cases of SARS.
A suspect case is a person who develops fever, cough, shortness of breath or difficulty breathing within 10 days of returning from travel to areas in Asia where SARS cases are being reported, or within 10 days of having had close contact with a 'probable' case of SARS. A 'probable' case of SARS is similar to a 'suspect' case, but the illness is more severe, with progressive shortness of breath and difficulty breathing and, in some cases, chest x-rays showing signs of atypical pneumonia.
We are beginning to learn more about the characteristics of the virus that presumably causes SARS. It is now clear that the virus can survive longer in the environment than was first thought. One study has shown that the virus can survive for at least 24 hours on a plastic surface at room temperature. This suggests that the virus can be transmitted through touching a contaminated tabletop, doorknob, lift button or other objects. But it is unclear whether the amount of virus which remains after 24 hours will be enough to infect someone.
Another study found that the virus could live for two days in human waste and urine at room temperature. This finding could probably explain why there was an outbreak in a Hong Kong apartment block where more than 320 people became infected, as there was a broken sewer line in that block. This is the only known case of environmental transmission, as all the other cases appear to have resulted from the transmission of the virus from one person to another.
Other tests show that the virus could survive for as long as four days in the faeces of infected people with diarrhoea, possibly because the faeces is less acidic.
At present, however, the primary mode of transmission of the virus still remains the droplet route, when an infected person sneezes or coughs, releasing virus particles into the air. In other studies, it was concluded that the virus could live for long periods in the cold when temperatures dropped to 0 degrees Centigrade, suggesting it could survive through a winter.
The complete DNA of the coronavirus (the molecular make-up of the virus that is believed to cause SARS) has recently been decoded and mapped by scientists at a Canadian research centre, a process completed with unprecedented speed. This could speed up efforts to diagnose, treat, and prevent the spread of the epidemic. It also increases the possibility of developing a vaccine for the disease.
A study by a team in Singapore has just shown that the virus has not mutated significantly in its spread to different countries.
Several laboratory tests, including serological testing, are used to detect the SARS-associated coronavirus, while viral culture and isolation have been employed to detect the virus. Interestingly, the virus is found in only about 40 per cent of SARS patients. Conversely, other people who are ill, but do not have SARS, have tested positive for the virus. As a consequence, scientists regard the performance of the diagnostic tests so far as poor.
An in-depth study of data from the outbreak in Hong Kong published in the Lancet medical journal indicates that SARS is probably more deadly than was originally thought. The new findings are based on a statistical analysis of 1,425 patients suspected of having SARS who were admitted to Hong Kong hospitals from February 20 to April 15.
The study confirmed that the elderly are particularly vulnerable, as the death rate was 43.3 per cent in those over the age of 60. In those under 60, the death rate was 13.2 per cent
WHO using data obtained from Canada, China, Hong Kong, Singapore, and Vietnam has now put the death rate at 14-15 per cent; the rate had previously been 6-10 per cent. The death rate seems to vary in countries with SARS. In Vietnam, where the outbreak is at an end, the death rate was 8 per cent.
And in Canada, where patients have been older, the death rate is 15 per cent. In general, the death rate is higher in people over 60 years of age, and lower in those under 40 years of age. And in Hong Kong, SARS seems to have a less aggressive course in younger children.
The Hong Kong study found that the incubation period - the time from infection to the time symptoms appear - averaged six days. Other statistical calculations had shown that the incubation period could be as long as 14 days.
Health officials had previously used 10 days as the longest incubation period. The incubation period is important, as health officials use it to determine how long people exposed to the virus need to be isolated. As a rule of thumb, health officials double the estimated incubation period to determine how long the period of quarantine should be, and when an outbreak can be declared over. An incubation period of 14 days would mean lengthening the quarantine period, and for declaring an outbreak over, from 20 days to 28 days. WHO has, however, decided for the present to use 10 days as the incubation period.
There is still some mystery as to the origins of the virus. Medical scientists have speculated that it was likely to have resulted from a 'species jump' from domestic livestock to humans. The UN Food and Agriculture Organisation in Rome has stated that there is currently no evidence to suggest that the virus originated in farm animals.
At present there is no cure or specific treatment for SARS. Hence, there is an urgent hunt on to find a drug that can stop the virus. The drug ribavirin, which is licensed for the treatment of other viral infections, is used by doctors in Hong Kong and Toronto who feel that it helps many SARS patients.
Tests in the United States, however, have found no evidence that the drug has any effect against the SARS virus. And it should be noted that this drug has significant toxic effects, and that it may do more harm than good.
There are only three dozen antiviral medicines on the market, but none is aimed specifically at the coronaviruses, the family that includes the SARS virus, as well as some that cause common colds.
Some of these drugs are likely to be tested for the treatment of SARS, but if none shows promise, one may have to be developed from scratch, a process that could take years.
Scientists say that the best long-term hope against the disease is the development of a vaccine. Even though the virus has been sequenced, it will take years to produce a safe and effective product.
In the absence of specific SARS treatment, the management of SARS patients at present entails keeping patients isolated and dealing with their symptoms while the infection runs its course.
Treatments have been empirical and patients have been given antibiotics, ribavirin, and corticosteroids. Those with severe breathing problems will need to be put on a ventilator.
