Medical Information

TRANSMISSION ROUTES AND RISK FACTORS

Available evidence suggests that SARS emerged in Guangdong Province, southern China in November 2002. More than one third of early cases, with dates of onset before 1 February 2003, were in food handlers.

Throughout the outbreak, the primary mode of transmission appears to be direct mucous membrane (eye, nose, and mouth) contact with infectious respiratory droplets and/or through exposure to formites. Cases have occurred primarily in persons with close contact with those very ill with SARS in health care and household settings. Transmission to casual and social contacts has occasionally occurred when as a result of intense exposure to a case of SARS (in workplaces, airplanes or taxis) or in high risk transmission settings, such as health care settings and households.

Under certain circumstances, such as in health care settings or other closed environments, contamination of inanimate materials or objects by infectious respiratory secretions or other body fluids (saliva, tears, urine and faeces have been found to contain virus) seems to occasionally play a role in disease transmission.

There have been no reports of food or waterborne transmission.

FOR HOW LONG WILL THE SARS VIRUSE EXIST ON SURFACES?

Virus is stable in urine and faeces at room temperature for at least 1-2 days, in stool from patients with diarrhoea for up to 4 days.
It survives on paper, a plastered wall after 36 hours, on plastic surface and stainless steel after 72 hours, on a glass slide after 96 hours.
Hospital environmental samples from a number of sites, including walls and the ventilation system, tested positive for SARS virus.
Virus loses infectivity after exposure to different commonly used disinfectants and fixatives. Heat at 56 C rapidly kills the virus.
The results of environmental sampling on the carpet outside room 911 in Metropole Hotel (the room in which the index case resided) and elevator area show a hot zone (possibly vomitus or respiratory secretions) which is PCR positive 3 months after the index case stayed at the hotel. Although the signal only demonstrated non-viable virus, this finding may have implications for the persistence of the virus in the environment.

Risk Factors for Transmission:

Health care workers especially in procedures generating aerosols.
Other risk factors :

household contact with a probable case of SARS
increasing age
male sex
presence of co-morbidities

Special populations:

SARS in children: Epidemiological investigation of 8 of 10 children with SARS in Hong Kong SAR who had been attending school at the time of presentation found no evidence that they had spread the infection to their classmates.

SARS in pregnancy: There had been no reported cases of vertical transmission (from mother to the foetus).

Airline transmission: A total of 29 secondary cases have been linked to probable cases of SARS who traveled while symptomatic.
WHO issued the first emergency travel advisory on 15 March to airlines and travelers, advising airline crew to report suspect and probable cases to airport and health authorities. Additional guidance was issued on 27 March recommending measures to reduce the risk of the global spread of SARS, including the exit screening of air passengers departing from areas reporting local transmission.

Since the travel advisory on 27 March, no transmission has been confirmed on flights although there have been at least 21 flights with probable SARS cases on board since that date.

Asymptomatic 'carriers': There are currently no reports of the transmission of SARS from asymptomatic individuals.

DOES ANIMALS TRANSMIT SARS?
A. DOMESTIC ANIMALS:

A number of animals (cats and dogs) living in Amoy Gardens tested positive for SARS-CoV. These were all pets exposed to high level of contamination.
Rats, mice, poultry, pigs and rabbits are resistant to infection but antibody levels are yet to be determined.
Rodent droppings collected during the Amoy Gardens investigation have tested PCR positive. However, there is no laboratory evidence that rodents can be infected.
SARS-CoV was detected on the body surface and gut contents of cockroaches by PCR. Cockroaches may act as mechanical vectors of virus transmission.
Further study is required to understand the role of domestic pets in the transmission of SARS.

B. WILDLIFE:

There is evidence that natural infection with SARS-CoV may occur in a number of animal species indigenous to China and parts of southeast Asia. Animals namely the masked palm civet, raccoon dog and the Chinese ferret badger were either found to contain coronaviruses or elicit antibodies against the SARS-CoV.
These and other wild animals are traditionally considered delicacies and are sold for human consumption in markets throughout southern China.

Information on the potential role of animals in the transmission of SARS is important to the overall understanding of SARS. It cannot be ruled out that these animals might have been a source of human infection.

CAN SARS BE TRANSMITTED BY FOOD?

Food has not been shown to be infective for SARS-CoV. However, symptomatic patients with febrile illnesses of any sort should not handle or prepare food for others.

WHO has issued the following advice following the finding of coronavirus-infected animals in southern China; “As a precautionary measure, persons who might come into contact with these species or their products should be aware of the possible health risks, particularly during close contact such as handling and slaughtering and possibly food processing and consumption.