Role of China in the quest to define and control severe acute respiratory syndrome - Perspectives

Emerging Infectious Diseases, Sept, 2003 by Robert F. Breiman, Meirion R. Evans, Wolfgang Preiser, James Maguire, Alan Schnur, Ailan Li, Henk Bekedam, John S. MacKenzie

Extensive seroprevalence studies will be helpful for sorting through these possibilities. Analyzing stored serum samples, collected before the onset of this outbreak, could be of immense value in evaluating the possibility of pre-existing immunity. Some researchers have found human metapneumoviruses (7) and species of Chlamydia in patients with SARS, but the importance of these findings is unclear. Systematic evaluation of specimens available from all cases, severe cases, and healthy controls in China regarding the presence of antibodies to coronavirus, as well as hypothesized co-infecting agents, should be done.

Important clues may come from seroprevalence and other epidemiologic studies in children. As in other affected countries, children were disproportionately less affected by SARS than adults. Carefully working through the bases for reduced incidence and severity may uncover cross-protecting infectious or immunizing agents or crucial host factors for protection.

Super-Spreading Events

When documenting the source of person-to-person transmission of SARS has been possible, a substantial proportion of cases have emanated from single persons, so-called super-spreaders (1). While contact tracing is undoubtedly incomplete, most infected patients have transmitted illness to few other people. Understanding the differentiating characteristics of persons who transmit, especially patients who are able to transmit to several other people, often after minimal contact, may provide important clues for public health strategies focused on preventing transmission. In addition, better defining environmental settings or circumstances that facilitate high transmission rates would be helpful. China is not unique in documenting super-spreaders. The country could participate in multinational studies to define the characteristics of super-spreaders and their role in the epidemiology of SARS. Of particular interest is the virus load of super-spreaders, compared with those of other infected persons.

Little is known about the importance of fecal-oral transmission or about the length of time that infectious virus shedding occurs in the gastrointestinal tract. Virus shedding in feces has major implications for control strategies and for the possibility of continued carriage and shedding by clinically recovered patients. China has the opportunity to explore the role of fecal spread in the transmission of SARS.

Evolution of the Virus

The causative agent is a coronavirus (8-10), and the entire genome of several strains has been fully sequenced by many laboratories globally (2,3,11). Tests have been developed to detect coronavirus genetic sequences by PCR. In addition, tests to detect SARS-associated coronavirus antibodies have been developed, but the sensitivity and specificity of these tests are low, especially early in the illness when public health and clinical needs are greatest. A good test for SARS would be important not only for diagnosis and management but also for investigating the origin of the disease and for defining its epidemiology.