Do you discern any relationship between city location and spread of the disease?

The scientists also studied 55 patients admitted to a hospital in Guangzhou, Guangdong Province, in early 2003 with atypical pneumonia. These patients ran fevers for an average of 11.4 days (+ 6.8 days, standard deviation) and developed pneumonia within 4 days of being admitted. Forty-one of 55 were known to have had definitive contact with another SARS patient, and 27 were healthcare workers. Guan and his colleagues examined mucus and blood serum samples for the SARS coronavirus antibodies. For 22 of the patients, the scientists tested paired samples, the first either 3 to 5 or 7 to 10 days after disease onset, and the second 15 days after onset. The researchers also tested 60 healthy adults (Table 22.9). Four of the pneumonia patients who did not test positive for the SARS coronavirus antibodies were discovered to have influenza.

Table 22.9 Antibodies against coronavirus in SARS and control patients. Table 2 from Zhong et al., 2003, reprinted with permission from Elsevier.

Integrating Questions Do you discern any relationship between city location and spread of the disease? What do the observations that many healthcare workers and family groups became infected suggest? What might be the mode of transmission of the coronavirus, or the way that SARS spreads? What do you think is the significance, if any, to the observation that the second known case of SARS was a chef who handled live animals from open air markets? Do the antibody results support the conclusion that the outbreaks were caused by the SARS coronavirus?

 
The study of the initial outbreak is an important part of epidemiology and can pinpoint the origin of an epidemic, identify modes of transmission, and identify possible origins of the pathogen. In the southern China SARS outbreak of 2002, several observations were made by epidemiologists that were clues to origins and modes of transmission. One observation was that the second known SARS patient was a chef who came into regular contact with live caged animals. The epidemiological investigation discovered that his wife, two sisters, and seven healthcare workers all became infected from him.
In fact, 34% of all patients in the outbreaks in the initial six cities were healthcare workers. A patient in Guangzhou who spent only 18 hours in a hospital in Zhongshan infected 30 healthcare workers in Zhongshan and Guangzhou. This patient also infected 19 family members or relatives in Guangzhou. This large number of infections in relatives and healthcare workers gave rise to the Guangzhou outbreak. One physician infected during this time traveled to Hong Kong and became the source of the SARS outbreak that occurred later in Hong Kong. Because the outbreaks were characterized by infections in hospitals and family units, Guan and his colleagues concluded that transmission occurs through close contact with infected patients. The spread from city-to-city occurred because of transport of patients to better hospital facilities and movement of workers from city-to-city. This is comparable to a parasite like Giardia, which you discovered is transmitted through fecal-oral contact or contaminated water.
If you concluded that close person-to-person contact was the mode of transmission, you might have also concluded that coughing or sneezing, which spreads small droplets up to about a meter from infected persons, disperses the virus. The virus only needs to land on the mouth, nose, or eyes of a nearby person for them to become infected. If droplets land on another person’s hands, or if an uninfected person touches a surface contaminated with droplets and then touches their mouth, nose, or eyes, they can become infected. Close contact may also mean kissing or hugging between an infected and uninfected person. These are thought to be the most likely routes of transmission.
Most patients with atypical pneumonia that were tested for the SARS coronavirus had it. Several were infected with a strain of the influenza virus. Given the large percentage of patients in this study with the SARS coronavirus, Guan and his colleagues concluded that the outbreaks were caused by this newly emerging viral pathogen. The scientists were able to conclude that the pathogen was emerging because none of the healthy patients had antibodies to the SARS coronavirus, which suggests that the virus was not previously present in this human population. The researchers, in attempting to track down the origin of the SARS coronavirus, focused on the second known SARS patient, the chef, and the observation that he came into contact with exotic game animals. In China and many other countries, wild animals are caught or raised in captivity to be sold live at markets for human consumption. Some wild game animals are considered a delicacy in southern China and are bought by chefs for preparation at their restaurants. Other diseases are also known to spread from animals to humans.