SARS epidemic created a medical emergency and a healthcare crisis with the loss of hundreds of lives in a short span of time. The knowledge of the etiology of the disease and the genome sequence of the virus provided new impetus in treatment of the disease. The crisis was successfully managed through an international cooperative effort and today we are better prepared to handle possible future outbreaks of the epidemic.
SARS is an acute infectious respiratory disease with all the symptoms of atypical pneumonia like fever, breathlessness that caused severe casualties in a short period of time. The first instance of SARS infection was reported in November 2002 in the Guangdong province of china. The SARS epidemic created a panic worldover and the World Health Organization issued a global alert on March 12th 2003 about the rapid spread of symptoms of atypical pneumonia. Symptoms of atypical pneumonia were reported in China and Hong Kong in February and March of 2003 and SARS created panic at the global level with 774 deaths and more than 8000 infected people. China, Taipei, Canada and Hong Kong suffered the most from the epidemic while sporadic SARS infections were found in many European nations and North America. Hundreds of people exhibiting symptoms were quarantined and treated for the complications until the SARS outbreak was fully contained. In July 2003 China officially announced the successful treatment of the last 12 cases of SARS. The present problem however is the early detection of the virus as the currently available diagnostic tools are either time consuming (ELISA and Immunofluorescence) or highly sensitive without any conclusive detection. (PCR). A discussion of the epidemiology, transmission, and the latest research results and treatment methods would provide a better understanding of the disease.
The SARS Virus
Ever since the spread of the epidemic in February 2003 laboratories worldwide were involved in research to hasten the identification of the agent that was responsible for the symptoms of atypical pneumonia. The World health organization instituted a combined research by eleven laboratories on March 17th to speedup the research, as by then, the virus was starting to take its toll. By the end of March researchers in Hong Kong managed to find out traces of a novel coronavirus in the affected patients. By means of cell culture, electron microscopy and immuno-fluroscent antibody tests researchers in United States and Germany also confirmed the existence of a special type of coronavirus. Coronavirueses have the largest genome size ranging from 27 kb to 32 kb and have been well-known to cause respiratory disorders in animals. Coronoviruses are easily transmitted by way of droplets, touch and small particulates in the air. They also have very short incubation periods as is the case with the SARS virus which has an incubation period between 2 and 7 days. On April 12th 2003 scientists working at the Michael Smith Genome Sciences center sucesfully mapped out the genetic sequence of the SARS virus making way for improvements in early detection and finding effective pharmacological treatment methods.
Clinical Course of SARS
There are two distinct phases observed in an infected person. The initial phase is that's of acquisition of the virus and the rapid multiplication of the same inside the host. The next phase is charaterized by persistence of symptoms due to immunological damage. During this stage symtoms may worsen and as a study by peris etal showed around 20%-36% of the affected people may require intensive care while 13 to 26% may require ventilator support for breathing. It is estimated that the IGg seroconversion starts around the 10th day and this is followed by rapid fall in the viral load.. The worsening of the symptoms during this phase is mainly due to the adverse response of the overactive immune system. [D SC Hui]
Symptoms and diagnostics
Typical symptoms for the SARS disease include raise in temperature (above 38 degrees), sore throat, breathing difficulty which becomes progressively acute, myalgia or muscle pain, sputum formation etc. There is a considerable drop in blood platelets and lymphopenia is commonly observed. All symptoms are manifest within the first two weeks of the onset of the infection. In severe cases (10 to 20%) there may be a need for mechanical ventilation to facilitate breathing as the lung function is severely impaired. Diagnostic procedures include a chest X-ray which would clearly indicate patchy appearance in the lungs. However chest X-rays taken during the initial few days would not show much differentiation from that of a healthy person and hence identification of lung infection by means of chest X-rays would only be possible in the later stages. [after a week] Finally, diagnosis in co-morbid conditions is difficult as the presence of other infections, may suppress the manifestation of symptoms.
Diagnostic methods became much easier after the SARS genome was successfully sequenced. Today we have Elisa, PCR (polymerase chain reaction) and the immunofluorescence array tests to identify the presence of the SARS virus. However, unlike other common virus infections, in the case of the SARS, virus shedding in excretion is very little in the early stages of the infection and hence detection by these tests is difficult. Since the currently available testing methods are not able to detect these small traces of virus shedding in the early phase of the disease, infection management still presents a huge problem. Of the three available diagnostic procedures the ELISA test detects the SARS antibodies in the specimen but only after a minimum of 21 days after the symptom manifestation and hence it is not much helpful from disease control perspective. Immunofluorescence assay test is comparatively quicker and takes 10 days to detect the antibodies but requires an immunofluorescence microscope. The best diagnostic is the PCR which can detect the presence of the viral DNA from any specimen such as stools, sputum, blood and other tissue samples. At present, in the absence of standard reagents for viral and antibody detection, we are largely dependent on epidemiological and clinical findings for diagnosing SARS in the early stages of the infection. [Kamps]
Transmission of SARS
Predominantly the SARS virus is transmitted via the respiratory secretions of the affected patients. Although fecal and airborne infections are also possible they are not so common. The rapid outbreak of the disease in 2003 which primarily affected the relatives of the infected persons and health care providers indicates that SARS disease is primarily spread trough direct contact of the affected persons. The virus is also detected in the stools of the affected persons and hence transmission through the drainage system is also a good possibility. Typically the viral discharge in stools peaks two weeks after the infection. Airborne transmission is considered mild although it cannot be totally excluded. Though the virus may have been transmitted from one person to another the degree of effect that the pathogen has on the host is determined by other factors. The actual manifestation of the disease depends upon factors such as the viral load (number of infectious viruses) received from the respiratory secretions or other infection carrying agents. So far, results from the RT PCR (Polymerase chain reaction) of the nasopharyngeal aspirates indicate that the viral load in the secretions are minimal in the initial few days of the infection and becomes substantial after 10 days. Given these facts the transmission rate of the virus is different during different stages of the infections.
In general the SARS virus is considered to be moderately transmittable as a study by avedano et al. has shown. The study observed 14 patients, who were all working in a healthcare setting and attending to patients who later developed SARS. During the initial stages when the patients exhibited mild symptoms they were not suspected for SARS and were treated as outpatients. These 14 patients had unprotected physical contacts with 33 people in their household for 4 days before the worsening symptoms forced them to critical care unit of the hospital. Inspite of the unprotected contacts only two out of the 33 exposed people developed SARS disease indicating that the infectivity is different during the different stages of the disease. [Monica Avendano] The high infection rate among healthcare workers suggests that prolonged exposure and exposure during acute stages of the disease leads to a high rate of disease manifestation. So SARS is not dangerously infectious but at the same time the infection rate is greater when the patient is in acute stages of the disease.
Epidemiology of SARS
Though the first instance of SARS was supposed to have occurred in November 2002 in Guangdong province of China, the first reported case of SARS was in February 2003 in Hanoi and in a few weeks patients exhibiting similar symptoms of atypical pneumonia were reported in Toronto, Hong Kong and Singapore. Initially the infection spread quickly because of poor understanding of the symptoms and the delay in hospitalization. However the Chinese government swung into action and immediately stepped up the preventive measures. Once the contagious nature of the disease…