Severe acute respiratory syndrome: An update

Abstract

The medical community will long remember the winter of 2002. An outbreak of an unusual form of respiratory illness started in the Southern Chinese province of Guangdong. It was characterised by a severe form of pneumonia caused by typical or atypical organisms. It also had a propensity to spread among household contacts and healthcare providers [1]. It spread quickly from mainland China, to Hong Kong, Taiwan, Singapore, Vietnam, Canada, USA and UK. The Public Health Specialist's nightmare of a rapidly spreading infection carried on the wings of modern jet airliner was a reality. A total of 8098 cases were reported, from 01 November 2002 to 31 July 2003 [2, 3]. India was also affected with three probable cases and 10 suspect cases reported. Statistics from the most affected regions are listed in Table 1. Table 1 SARS statistics (01November 2002 to 31 July 2003) The overall mortality rate was 11% and the attack rate was 53%. The disease mainly spreads by droplets or close person to person contact. Contact with contaminated skin, secretions and excreta of patients are also postulated to be the modes of spread. The rapid spread of cases in the Amoy Gardens Apartment complex in Hong Kong and Metropole Hotel in Singapore have raised questions about airborne and vector borne (rats) transmission [3, 4]. Majority of patients may not effectively transmit the virus, but some are “super-spreaders” and they transmit the virus to a large number of individuals [4]. These super-spreaders and nosocomial amplifications were responsible for the early 2003 outbreaks. Initially, the disease was thought to be a type of ‘bird flu', after all, an avian flu epidemic had occurred in Hong Kong in 1997. On 26 February 2003, a Chinese-American businessman was admitted to a French Hospital in Hanoi with fever, dry cough and difficulty in breathing. Dr Carlo Urbani (the World Health Organisation (WHO) public health specialist in Vietnam, who later succumbed to severe acute respiratory syndrome), attended him. The rapid deterioration in the patient's condition and occurrence of similar symptoms in ten other persons working in the hospital made him suspect that this was not a simple epidemic of avian flu. He notified the WHO and a team of experts was rushed to investigate the outbreak [5]. WHO also formed a Severe Acute Respiratory Syndrome (SARS) working group comprising of 11 research laboratories all over the world to try and identify the causative agent and develop diagnostic tests [6]. The initial suspects were a paramyxovirus and human metapneumovirus. These organisms were however found in only a few clusters of cases. The turning point was the detection of an agent that produced a distinct cytopathic effect on Rhesus monkey kidney cells [7]. Electron microscopy further revealed virus-like particles. The very next day, a laboratory in United States identified these to be corona virus particles. Primers against corona virus were used to test samples all over the world and a high positivity was reported. Three pathogenic families of corona viruses are known. They cause a number of veterinary diseases like porcine gastroenteritis, avian infectious bronchitis and feline infectious peritonitis. The human pathogenic forms usually cause a mild upper respiratory tract infection (human corona virus – hCoV 229E). The culture requirements and cytopathic effect of the viral particles isolated from patients with SARS were distinct from the known pathogenic strains. Hence the infection was thought to be due to a novel corona virus. Since then, the viral genome has been sequenced and many rapid diagnostic kits are available [8]. Koch's postulates have also been proven by growth and isolation of the virus in cynomolgus macaques[9]. Preliminary research suggests that the SARS – associated coronavirus (SARSCoV) may have originated in small mammals like the Himalayan palm civet or in livestock (chicken or duck). Mutation may have then allowed its transmission to humans. The proximity in which humans and livestock exist in rural China could have aided this process.