SARS-CoV: Epidemiology |
|
| Epidemiology Symptoms Transmission Incubation Period Infectious Period Risk Factors Case-Fatality Ratios Reservoirs Affected Regions Prevention Timeline Home Epidemiology Disease Pathology Diagnosis & Treatment The Pathogen Immune Response Vaccine Development Global Health Response References Disclaimer |
In November 2002, the emergence of a previously unidentified coronavirus challenged the global health community. First identified in Guangdong Province in Southern China, Severe Acute Respiratory Syndrome (SARS) quickly garnered international attention because of its severity and seeming ease of transmission. Yet, despite widespread fear about a SARS epidemic, it soon came to light that SARS is a disease that can be brought under control using simple, well known health measures. Coronaviruses (CoV), so named for their crown-like shape, have a long history of causing infection in humans and animals. In humans, coronaviruses are responsible for causing many respiratory tract infections and have been linked to gastroenteritis. While most coronaviruses are specific to only one species, it is possible that SARS-associated CoV is a mutated form of a coronavirus found in an animal that has contact with humans. (113) The most prominent symptoms of SARS are high fever and coughing or shortness of breath. Suspect and probable cases are identified as people who have had close contact with an infected person, or have had recent air travel or who have experienced other symptoms such as muscle soreness, headache, loss of appetite, diarrhea, or rashes. By August 2003, there were 8422 probable SARS cases, with 916 deaths in 32 countries. The first identified cases of SARS were in food handlers in Southern China. Many of the first patients had regular frequent contact with wildlife and domestic animals, a fact which has led many to believe that the SARS CoV is a modified version of an animal coronavirus. (46) Transmission occurs through mucous membrane contact with infectious droplets or fomites. In order to become infected, a person usually must have either close contact with an infected person (such as in a household), intense exposure (such as in a small area like an airplane or taxi) or have been in a high risk area (such as a health care setting). After studying the virus, SARS was given a basic reproduction number (R o ) of three, a relatively low number. This value is a measure of the potential of a disease to spread to susceptible populations when under no control measures; SARS can only travel a few meters, which limits its transmissibility. (113) The mean incubation period for SARS is four to five days. Although the World Health Organization (WHO) has guessed that the vast majority of those infected have an incubation period less than ten days, this information is questioned due to the nature of other known coronaviruses. (11) Other known human coronaviruses have been determined to have the ability to remain in incubation for much longer, which suggests that some of those infected carry the disease for longer than the WHO's current projections. (38)
SARS is most efficiently transmitted by a severely symptomatic patient. This happens on average within ten days. Maximal virus excretion occurs at about ten days in the respiratory tract and at about thirteen days in stool. SARS CoV can survive up to two days at room temperature and up to four days in stool. It can be fairly easily killed with heat or many common disinfectants. (11)21% of the cases globally were found to be in health care workers. Other possible risk factors include household contact with an infected person, old age, being male, nutritional deficiencies, and co-morbidity with other diseases, namely diabetes. Although highly publicized due to several cases of transmission, air travel is only associated with slightly increased risk. (113) Overall, infection with SARS-CoV has an eleven percent fatality rate, although these rates range from zero to fifty percent depending on the age group and co-factors measured. Infected people who are elderly face a greatly heightened risk of mortality once infected.
It is most likely that the SARS CoV crosses over to humans from a different species. When humans are in close contact with animals, coronaviruses have been known to recombine to become pathogenic to people. SARS CoV is genetically similar to coronaviruses found both in populations of palm civets and raccoon dogs. The main difference between the animal and human viruses is a 29 base pair sequence not found in the human strain. Although there is no conclusive evidence on where the SARS CoV originated, determining potential animal hosts is imperative to disease control. If the virus that causes human infection can be harbored in an animal host, complete eradication of SARS is much more difficult to achieve. Countries with the greatest number of cases are China, Hong King, Taiwan, Canada, Singapore, and Vietnam. (71)
The rapid identification and subsequent control of SARS would have been impossible if not for global collaboration and information exchange between governments and health care organizations worldwide. Quick access to the most updated information and shared scientific research led to more efficient and effective policies to halt the spread of SARS. Rapid reporting of cases to the WHO, continued collaboration, development of and adherence to internationally developed guidelines, use of quarantine, contact tracing and efforts to decrease the time between the advent of symptoms and hospital admission are a few key areas that are integral to preventing the spread of SARS. For individuals and health care workers in particular, personal protective equipment (PPE) such as gloves and respirators and basic hygiene habits (hand washing, etc.) are the most important step in preventing the transmission of SARS. (20) Future work in prevention must focus on finding a vaccine to combat SARS, developing tests for early detection, and understanding the nature of any potential animal reservoirs. February 10, 2003 Chinese officials publicly admit that a disease resembling pneumonia has killed five people and affected 305 others since November 2003 March 12 WHO declares a global health alert after cases resembling Chinese infection are reported among health workers in Vietnam and Hong Kong March 15 Center for Disease Control (CDC) advises Americans to avoid all non-essential travel to avoid spread of the new pneumonia, which touched off a massive cutback in traveling to endemic regions, WHO declares SARS a worldwide health threat March 24 CDC first declares that SARS is likely caused by a novel coronavirus March 27 WHO recommends rigorous screening of all air travelers April 5 China apologizes to the global community about their evasiveness and slow initial reporting of SARS April 14 Canadian researches first report sequencing the SARS genome April 16 WHO confirms that SARS is caused by a coronavirus, which they name the "SARS virus" June 5 WHO declares that the outbreak has peaked globally July 5 Taiwan is the last country to be removed from WHO list of infected areas and WHO declares that the outbreak has been contained, although not eliminated. January 16 Evidence found by the WHO that civets carry a similar strain of SARS as humans |
