Severe Acute Respiratory Syndrome (SARS): Is the threat really over?

On 15th of March, 2003, the World Health Organization (WHO) issued a rare travel advisory on a new disease named as "Severe Acute Respiratory Syndrome (SARS)", declaring it "a worldwide health threat", advising airlines that if a passenger or crew member met the SARS criteria, the aircraft should alert the destination airport, and on arrival the sick passenger should be referred to airport health authorities for assessment and management.[1] Although the main focus of illness was China and other Far-Eastern countries, however, cases were reported from all over the world, legitimizing such a global warning. After the recommendations, all countries with local transmission or imported cases were able to either prevent further transmission or keep the number of additional cases low through immediate isolation, strict infection control, and vigorous contact tracing. On the 5th of July 2003, WHO announced that all known chains of person-to-person transmission of the SARS virus had been broken and the world could have a sigh of relief, at least for the timebeing.[2] However, the question remains whether this is really the end of SARS? Or is there a possibility for the disease to resurface?

SARS is caused by a new coronavims, SARS-CoV, of the Coronaviridae family, an enveloped positive stranded RNA virus, with a high rate of genetic mutation.[3] In the absence of any specific evidence for the existence of animal or other environmental reservoir, the sole transmission of SARS is attributed to human to human.[4] The primary mode of transmission appears to be droplet infection through close person-to-person contact or direct contact with infectious material of a SARS patient. Its incubation period ranges between 2 to 10 days (average 2-7 days).[4]

Keeping in view the seriousness of illness, a highly sensitive case definition was adopted for surveillance. A suspect case was defined as a person presenting after 1 November 2002, with history of high fever (>38°C) and cough or breathing difficulty and one or more of the following exposures during the 10 days prior to onset of symptoms (a) close contact with a person who is a suspect or probable case; (b) history of travel to an area with recent local transmission; (c) residing in an area with recent local transmission. A probable case was defined as a suspect case with one or more of following (a) radiographic evidence of infiltrates consistent with pneumonia or respiratory distress syndrome on chest X-ray; (b) positive for SARS coronavirus by one or more assays; (c) have autopsy findings consistent with the pathology of RD S without an identifiable cause.[5] In May 2003, WHO declared an overall estimate of case fatality of 14-15%. The case fatality ratio was estimated to be under 1% in persons aged 24 years or younger, 6% in persons aged 25-44 years, 15% in persons aged 45-64 years, and over 50% in persons aged 65 years and older. However, on the basis of all the cases reported by the end of June 2003, an overall case fatality ratio of 9.6% was calculated.[6]

Even though high cure rates have been demonstrated with a treatment regimen including antibacterials (levofloxacin/clarithromycin), antivirals (ribavarin) and methylprednisolone in a small group of patients, the mainstay of treatment is non-specific supportive management as a case of atypical pneumonia.[7]

It is now known that the first cases of SARS appeared in Guangdong province of China in mid-November 2002. However, the first report by the Government of China to WHO was on 11-2-2003, with 305 cases of atypical pneumonia, negative for Influenza virus, and 5 deaths. Around 30% of cases had occurred in health care workers.[8] Initially, the outbreak was confused with Influenza A (H5N1). By the time disease was recognized as SARS, it had already spread from Guangdong to Hong Kong and from there to Canada, Vietnam, Singapore and Germany. The main international transmission was along air travel routes, which instigated the WHO to issue the global travel advisory. On the 2nd of April 2003, the WHO recommended that persons traveling to Hong Kong and Guangdong province consider postponing all but essential travel until further notice, the most stringent travel advisory by WHO in its 55-year history. Later it was expanded to other countries, depending on the evidence of local transmission.[8] Initially, China was slow to report cases, but later on developed an efficient system of reporting and response, with high political commitment and community involvement.

After the global alert, only 1 major outbreak occurred despite initial exported cases to a total of 32 countries.[8] The outbreak which started in Mid November, 2002, has apparently terminated with the last case occurring on 12th June, 2003 (Fig. 1). As of the 4th of July, a total of 8439 cases of SARS had been reported from these 32 countries. The highest numbers were reported from China Mainland (5327), Hong Kong special administrative area (1755), Taiwan (674), Canada (251), Singapore (206), USA (73) and Vietnam (63). Outside China and the Far East, Canada was the only country with local transmission of the disease. The last probable case was reported from Canada on 27th of June, which had a date of onset of 12th June.[7] In the GCC countries only one probable case was reported from Kuwait on 9th of April, while no probable case was reported in the Kingdom of Saudi Arabia despite active surveillance in all its airports.[7]

SARS has adversely affected the economies of East Asian countries and Canada through effects on tourism, travel, health and trade. Despite certain uncertainties, the World Bank has estimated a direct impact effect of 0.4-0.5% of GDP, with multiplier effects on employment and consumer and investment confidence bringing the estimated cost of SARS in the range of $20-25 billion in East Asian countries, with the maximum cost for China and Hong Kong.[8]

Regarding disease etiology and transmission, a lot of epidemiological work needs to be done. However, we should learn a few lessons from the SARS epidemic ;[4,8]

Today we cannot be sure whether SARS will reemerge, but we can be confident that if it does we will be better prepared to handle it more efficiently with minimal damage, provided we do not lower our guards.