The 2003 SARS outbreak: epidemiology, etiology, and global spread

Communicable Disease/Community Nursing

2003 SARS Outbreak

In November 2002, the first case of severe acute respiratory syndrome (SARS) was reported in the Guangdong Province in China (Lau and Peiris, 2005). Over the next few months, SARS cases were reported in over two dozen countries in Asia, South America, Europe, and North America (CDC, 2004a). The biggest concentration of SARS cases appeared in Singapore, Hong Kong, Taiwan, and Canada (Totura and Baric, 2012). By July of 2003 the epidemic had been controlled through health measures. Overall, there were 8,096 confirmed SARS cases with a mortality rate of 9.6%.

SARS Etiology and Clinical Presentation

SARS is a respiratory disease caused by a coronavirus infection, a virus consisting of a protein capsule containing an RNA viral genome (Totura and Baric, 2012). Believed to transmissible between humans through respiratory aerosols and physical contact, the febrile disease initially presents with a cough and sore throat. These symptoms are consistent with the virus entry point being respiratory ciliated epithelial cells.

What distinguished SARS from seasonal influenza is that most patients developed pneumonia (CDC, 2004a) and approximately 25% progressed to acute respiratory distress syndrome (ARDS) (Totura and Baric, 2012). The elderly were most susceptible to developing ARDS (50%) and ARDS patients had a mortality rate over 50%. ARDS in SARS patients was characterized by pulmonary edema, severe hypoxia, an immune infiltrates in the lungs. Further worsening of the disease led to multiple organ failure and then death.

SARS Epidemiology

Using retrospective serological analysis, the first index SARS case was traced to an adult male in Foshan, just west of Guangzhou (Zhao, 2007). He was hospitalized on November 12, 2002 and had infected his wife and three other relatives. The first confirmed case of SARS was a chef working in Shenzhen and he was hospitalized on 15 December, 2002. As a result, seven hospital staff and one patient were infected. During the end of December and the beginning of January, atypical pneumonia cases sprang up throughout the Pearl River Delta surrounding the main city of Guangzhou. The SARS case map in the Pearl River Delta region between mid-November 2002 and mid-January 2003 does not indicate a clear spread pattern, but only isolated cases. However, it was clear that all cases were west of the capital city, Guangzhou, an area undergoing rapid economic development, including a blossoming trade in exotic animals.

Beginning about mid-January, the number of SARS cases increased 5-fold (Zhao, 2007). The relatives of infected individuals and hospital staff began to be infected at an alarming rate in China. A patient traveled to Hong Kong and stayed in a hotel, where it is believed he infected hotel guests and staff (Figure 1). This event is believed to be the primary one leading to the global spread of SARS to Singapore, Taiwan, Canada, and Europe.

COMMUNICABLE DISEASE/COMMUNITY NURSING

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Figure 1: Spread of SARS during 2003 Global Outbreak. Left Panel: the initial spread through the Pearl River Delta region to Hong Kong. Right Panel: Once SARS had arrived in Hong Kong, it then spread to Taiwan, Canada, Europe, and the rest of China.

Researchers retrospectively identified the likely zoonotic reservoirs of the disease by examining the epidemiological data of the infected individuals in the Guangzhou region (Zhao, 2007). The increasing affluence of the western Pearl River Delta region had fostered an increased in trade in exotic animals for pets and restaurant fare. Of the 10 independent index cases occurring in this region, at least six had handled animals. Serological tests of a number of animal species, including chickens, pigs, snakes, bats, monkey, ferret, rabbit, cats, and rats revealed no virus or were inconclusive; however, experiments with palm civets and raccoon dogs revealed that these species were very efficient in transmitting the disease through saliva. Retrospective testing of civet farm workers in the region revealed that 40-78% were seropositive for SARS. The implications of this result are that most individuals infected with SARS from wild animals remained asymptomatic.

The SARS genomic sequencing studies also revealed that the civet-derived virus was not very pathogenic, but once the virus has begun to replicate in human hosts, it quickly became virulent (Zhao, 2007). Once this pattern was revealed, the Chinese government instituted a permanent ban on wild animal markets in the Pearl River Region. This resulted in a dramatic decline in SARS seropositivity in animal and restaurant workers, from 25% in 2003 to 5% by mid-2004.

Based on the above epidemiological analysis, my community would not be the source of a future SARS outbreak because a wild animal market does not exist. However, given the global nature of travel in the modern world the threat of SARS in my community is not zero. SARS could emerge again in Asia or anywhere wild animals are handled. There are a number of zoos and wild animal parks across the United States that could be a source of SARS. While quarantine procedures and serological testing will probably prevent such an event from occurring, the smuggling of exotic animals in the United States does occur. Luckily, the virus needs time to adapt to a human host before it becomes virulent enough to cause severe disease and spread rapidly through human hosts. With the world now on guard against another SARS outbreak, the chances are increased that infected individuals will be tested and quarantined before the disease can spread.

Management of Respiratory Patients during Poor Air Quality Events

Outdoor air pollution represents a significant risk for premature death for all people, but during short-term increases in air pollution patients suffering from respiratory and cardiovascular disease will disproportionately visit emergency rooms and be admitted to hospitals due to respiratory and cardiovascular distress (reviewed by Abelsohn and Stieb, 2011). The primary outcome of increased air pollution levels for patients with asthma, chronic obstructive pulmonary disease, and heart disease, is an exacerbation of symptoms and increased mortality. The symptoms that can develop can include pulmonary inflammation, obstruction, infections, and allergic symptoms. For cardiovascular patients, heart rhythms, blood pressure, vascular tone, and clotting activity can be altered. Overall, these symptoms are consistent with an air pollution-induced increase in systemic inflammation.

The main pollutants of concern are ozone, particulate matter (< 2.5 ?m in diameter), and nitrogen oxides (reviewed by Abelsohn and Stieb, 2011). The main source of these pollutants is roadways, but the concentration of these pollutants drop off considerably after about 150 meters distance. Persons with respiratory and cardiovascular disease should therefore avoid spending time near roadways, especially during periods of elevated pollution levels.

Other significant sources of air pollution include power and industrial plants burning fossil fuels, forest fires, and wood burning stoves and fireplaces (reviewed by Abelsohn and Stieb, 2011). Individuals suffering from respiratory and cardiovascular disease should avoid spending time outdoors on days when pollutant concentrations reach levels that have caused health problems in the past.

Urban pollution levels in the United States and Canada can be monitored using the Air Quality Health Index (AQHI), which can be accessed through the appropriate government agency, online, and through news channels (reviewed by Abelsohn and Stieb, 2011). Patients with respiratory and cardiovascular disease should monitor the severity of their symptoms in relation to the AQHI, thereby allowing them to use the AQHI to predict periods when spending time outdoors or certain activities would exacerbate their symptoms. Monitoring the AQHI will reveal that some patients react adversely to even low levels of air pollution, depending on what activities they engage in and how much time is spent outdoors.

Once a patient learns how their symptoms react to air pollution levels, as determined by the AQHI, they can adjust their outdoor activities accordingly (reviewed by Abelsohn and Stieb, 2011). For example, patients who are still physically active may want to reschedule a strenuous outdoor activity to periods when pollution levels have returned to a lower level or move the activity indoors. Patients with more severe disease may benefit from avoiding outdoor activity altogether, closing the windows, and utilizing a filtration system capable of removing many of the pollutants discussed above.