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Monday, June 02, 2003

Health

A New Epidemic


In November 2002, a businessman from the city of Foshan in the southern Chinese province of Guangdong might have been the first victim of a mysterious illness called severe acute respiratory syndrome (SARS). Guangdong has a population of 75 million and thousands of farms with large and small animals in a subtropical climate. The first patient and many others received no attention until February 2003. A doctor from the province became ill while staying in a hotel in Hong Kong. Twelve other hotel guests became infected, many of them after staying on the same hotel floor as the doctor. These individuals transported the disease to Vietnam, Singapore, Canada, Ireland, and the United States. On February 28, the Vietnam French Hospital in Hanoi contacted the World Health Organization to report a patient who had become ill with flu-like symptoms. In a matter of weeks, this patient and six other healthcare professionals would be dead. With similar reports coming out of the other countries at the same time, an epidemic was born.

“Epidemic” comes from the Greek epidemios, which means prevalent, and it is defined as occurring suddenly, in numbers clearly exceeding normal expectation. The word is used especially in the context of infectious diseases but can also be applied to other diseases or events. SARS is a classic epidemic: as of April 17, 2003, there were 3,389 cases and 165 deaths (a death rate of 4.9 percent) recorded in 27 countries.

In general, SARS begins with a fever greater than 100.4 degrees Fahrenheit (or 38 degrees Celsius). Other symptoms might include headache, an overall feeling of discomfort, and body aches. Some people also experience mild respiratory symptoms. After two to seven days, SARS patients can develop a dry cough and have trouble breathing. Clearly, this symptomatology is very broad. Many colds and “grippe” illnesses that are common in winter have the same symptoms as SARS, making it difficult to identify cases as definitely belonging to the syndrome.

The primary way that SARS appears to spread is by close person-to-person contact. Most cases have involved people who cared for, lived with, or had direct contact with infectious material (respiratory secretions, for example) from someone who has SARS. Potential ways in which SARS can spread include touching the skin of other people or objects that are contaminated with infectious droplets and then touching your eye(s), nose, or mouth. This can occur when someone who has SARS coughs or sneezes droplets onto themselves, other people, or nearby surfaces. It is also possible that SARS can spread broadly through the air or in other ways that are currently not known.

Most cases of SARS in the US have occurred among travelers returning to the country from other parts of the world. There have been very few cases resulting from close contacts with family members or healthcare workers. Currently, there is no evidence that SARS is spreading more widely in the United States.

Scientists at the Centers for Disease Control and Prevention and other facilities believe that a leading hypothesis for the cause of the disease is a previously unrecognized coronavirus that they’ve detected in SARS patients. Coronaviruses are a group of very common viruses responsible for up to 30 percent of colds in humans, but they rarely cause pneumonia or diseases like SARS. Coronaviruses are found in nature and cause illness in many animals, including pigs, cattle, dogs, cats, and chickens. Laboratories have identified a new coronavirus in SARS patients from seven different countries. This virus is unique: through genetic technology, it has been found to be only distantly related to previously known coronaviruses. Additional evidence is now being collected using studies on blood from patients and non-patients.

Briefly, the antibodies created by our immunological system to respond to bacteria and viruses persist for a long time, often for life, after we’ve been exposed to infection. Antibodies to the SARS virus, however, have not been found in human samples collected prior to the SARS epidemic. Additionally, SARS patients have not had antibodies to this virus early in the infection but have developed them later, supporting the assumption that they are fighting a new coronavirus. It appears that this virus has not previously circulated in humans. It is possible that it comes from an animal that has somehow acquired the ability to infect humans. (This theory undoubtedly sounds familiar, given the other epidemic of the last 25 years, HIV). Theories abound, including that the proximity of humans to animals in southern China might have caused a mutant animal virus to cross species, resulting in the epidemic.

A combination of factors has likely contributed to the epidemic: a previously unknown virus, a highly mobile and global population, and the Chinese government’s acknowledged failure to respond to the crisis in a timely fashion. Once the news of a possible epidemic became known, however, the speed of scientific discovery and the global dissemination of information were impressive. Within only one month of the initial reports from Guangdong, the new virus was identified. The Internet and the international media’s role in continually disseminating information likely aided the efforts to prevent further spread of the disease.

To contain a contagious illness, public-health authorities rely on many strategies, including isolation and quarantine. Both are common practice in public health and both aim to control exposure to infected or potentially infected individuals. Both might be undertaken voluntarily or compelled by public-health authorities. The two strategies differ in that isolation applies to people who are known to have an illness, while quarantine applies to those who have been exposed to an illness but might not yet be infected.

Isolating people with a specific illness separates them from healthy people and restricts their movement to stop the spread of the disease. Isolation also allows for the focused delivery of specialized healthcare to people who are ill, while protecting the healthy. People in isolation may be cared for at home, in hospitals, or at designated healthcare facilities. Isolation is a standard procedure today and, in most cases, is voluntary; however, many governments have the basic authority to compel isolation of the sick in order to protect the public.

Quarantine, in contrast, applies to people who have been exposed but might not yet be infected. Separating exposed people and restricting their movements is intended to stop the spread of illness, and is medically very effective in protecting the public from disease.

SARS patients are being isolated until they are no longer infectious. This practice allows patients to receive appropriate care and contains the spread of illness: those who are severely ill are cared for in hospitals, while those whose illness is mild are cared for at home. Individuals being cared for at home have been asked to avoid contact with other people and to remain at home until 10 days after the resolution of fever, provided respiratory symptoms are absent or improving.

There are no current therapies that are effective against SARS. In contrast to infections caused by bacteria for which there are numerous antibiotics available, viral infections are more difficult to treat with medication. Nevertheless, vaccination strategies have been effective for viral diseases (including polio, smallpox, and measles) and there is reason to be optimistic about future vaccines for SARS. In the event, as the SARS epidemic is young, it is difficult to predict how extensive or serious it will be. It might prove to be controllable and cause disease like other respiratory viruses (for example, influenza) on a yearly, seasonal basis — or it might exhaust our scientific and technological capacities.

Theoklis Zaoutis is attending physician in special immunology (pediatric HIV) at the Children’s Hospital of Philadelphia and an investigator for the Pediatric AIDS Clinical Trials Group (PACTG). He is also a fellow in pediatric infectious diseases at the Children’s Hospital of Philadelphia and an instructor in the department of pediatrics at the University of Pennsylvania School of Medicine.
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