Changing Virulence of the SARS Virus: The Epidemiological Evidence

Article excerpt

Severe acute respiratory syndrome (SARS) is a newly described, deadly, communicable disease, first manifested in an epidemic that started in November 2002 in Guangdong Province, China (l). A medical professional who had worked with SARS patients in Guangdong visited Hong Kong on 21 February 2003. The disease quickly spread to 26 countries with local transmission in Singapore, Hanoi, Hong Kong and Toronto. The agent of SARS is an RNA coronavirus, not seen before in humans, known as SARS-CoV (1). The virus has been isolated from specimens (2); the genome has been sequenced (3); and infectivity in monkeys has bean demonstrated. At the end of the 2003 epidemic, 8098 possible cases and 744 deaths were reported to WHO (4).

Although SARS has been controlled, the potential evolution of this virus is not weft understood. This paper reviews the epidemiological characteristics of the epidemic; inconsistencies in transmissibility and mortality, the molecular epidemiology of SARS-CoV (4), the results of mathematical modelling, and evidence of evolution towards virulence in pathogens in similar settings.

Transmission

The epidemic probably started in mid-November 2002 in Fushan City in southern Chinas Guangdong Province (4, 5) where at least two patients had atypical pneumonia of unknown cause. Immediately, similar cases were reported in five cities in Guangdong. A 35-year-old male patient who worked in Shenzhen as a chef was transferred to Heyuan People's Hospital in Heyuan City where he infected at least 11 people. In Guangdong, there was no official recognition of a possible public health problem, and limited containment measures were implemented. On 11 February 2003 the provincial health department held a news briefing and stated that 305 cases had been reported and five people had died; these statistics were later revised to 792 cases and 31 deaths.

A 64-year-old male physician who had been treating SARS patients in hospital in Guangdong travelled to Hong Kong on 21 February 2003, having experienced symptoms five days earlier (6). He checked into the Metropole Hotel, and the following day he was admitted to an intensive care unit. He died on 4 March (7). Before being admitted to hospital, he infected his brother-in-law and 10 people in the hotel (6) including three women from Singapore, a 78-year-old woman from Toronto, a man from Vancouver, a Chinese-American man (who was the sole index patient for the SARS outbreak in Viet Nam), a 26-year-old man from Hong Kong (who was admitted to the Prince of Wales Hospital and infected the index patient from the Amoy Garden Apartments) (8); two Hong Kong residents, and a man who transmitted the infection to his wife.

From these early cases the epidemic spread globally. A 27-year-old Shanxi businesswoman travelled to Guangzhou on 18 February; she became ill on 22 February and was admitted to hospital in Beijing, infecting many heath-care workers. A doctor at this hospital wrote to Time magazine in early April to alert the public to the fact that Beijing had many unreported cases of SARS, prompting the government to implement control measures in Beijing (9). A 72-year-old Beijing man became ill in Hong Kong, and on 15 March he took a flight back to Beijing, spreading the virus into Inner Mongolia, Hebei and Tianjun (9). A person infected at the Amoy Garden Apartments later spread the virus to the Taiwan Peace Hospital in early April.

Several themes have become apparent in tracing the spread of this disease:

* health workers comprised the majority of cases (10), the remainder were members of the same household as an infected person;

* close and/or repeated contact was required for the disease to be transmitted from person to person;

people who infected more than 10 people spread the disease into new geographical areas;

* the number of people who became ill after exposure varied greatly, from 0 to >30;

* the transmission of the virus from Beijing to Shanghai and between Guangdong and Hong Kong was unexpectedly limited (occurring three months after the first cases), despite the large amount of travel that occurs between these areas (11). …