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Letter
Transmission of Severe Acute
Respiratory Syndrome
Isao Arita,* Kazunobu Kojima,† and Miyuki Nakane*
*Agency for Cooperation in International Health, Kumamoto, Japan; and
†Sapporo Medical University School of Medicine, Sapporo, Japan
To the Editor: The worldwide pattern of severe acute respiratory
syndrome (SARS) transmission in 2003 suggests that transmission has occurred
more frequently in communities that share certain social and cultural
characteristics. Of 8,500 probable cases since March, >90% were reported
from China (including mainland, Hong Kong, and Macau) and Taiwan. Of the
other 27 countries reporting SARS occurrences, 23 reported <10 cases
and the others 1–3 cases. The small number of transmissions in these other
countries suggests that the close contact required for transmission did
not occur, whereas in China, community-based transmission has continued.
In contrast, the relatively large number of cases in Canada, the United
States, Singapore, and Vietnam (which comprise 7% to 10% of the total
SARS cases worldwide) is related to the fact that relatively prolonged
contact occurred because of the patients’ close cultural ties with China.
Why does Japan still have no cases of SARS, despite its geographic proximity
to the most affected areas? We suggest that transmission has not occurred
because Japan remains a society mostly closed to non-Japanese persons
and has a history of casual contact between its citizens and the travelers
and noncitizens who reside there.
Hospitals have functioned as junctions for varied communities in spreading
the SARS virus further. Because of SARS’ likely place of origin, the initial
“community” included Chinese persons who then kindled the chain of transmission
to other communities throughout the world. Daily, close contact between
SARS patients and hospital personnel led to an unusually large number
of infections among medical staff members. Effective prevention measures
such as vaccines are not available and may be a factor in the spread of
the infection.
Even in the era of globalization and mass air transit, most persons live
inside a relatively small circle of community, made up of others of similar
ethnicity, religious beliefs, educational level, and social class who
live in the same vicinity; this sort of small circle has been described
as “mutual coexistence” by anthropologist Kinji Imanishi (1).
Basically, the SARS-associated coronavirus began circulating among members
of such a community. This theory does not suggest that certain ethnic
groups are predisposed to be susceptible to SARS.
Why have few cases of SARS occurred in children? All age groups are susceptible
to the SARS virus, which is new to humans. However, adults have more chance
to become infected through contacts in their daily lives, whereas children
do not. Rapid isolation of the adult patients contributed to reduced frequency
of exposure for children in that household, which is in contrast to the
usual infectious diseases of childhood (since children do not have immunity
against many age-old microbes).
Some contradictions exist for our interpretation of the SARS transmission
pattern. Investigations have shown that in Canada, Hong Kong and elsewhere,
some casual brief contact caused the infection or that the link between
the source and the case was not at all clear. We may have missed other
important routes of transmission, or a totally unknown element may be
involved. Without an answer for this discrepancy, we note that the clinical
virology for SARS, such as pattern of virus shedding and host immune response,
is still developing (2). For example, a total of 19 cases
in China were identified as SARS by coronavirus isolation, polymerase
chain reaction, or serologic tests. For two case-patients, the results
of three tests were positive; 10 case-patients had negative test results;
and in 14 case-patients, the virus was not isolated. Interpreting these
results is difficult. In the United States, 97% of the probable cases
were attributed to a recent history of international travel to SARS-affected
areas. Antibodies to SARS-associated coronavirus were demonstrated for
8 of 41 probable case-patients in convalescent-phase serum, bringing the
proportion of laboratory-confirmed cases to 20%, even in the probable
cases, and 0% among the suspected cases in the United States so far (3).
These results are the best available by laboratories with the current
limited technical knowledge. We are not persuaded that casual contact
with SARS patients in unfamiliar settings results in contracting the disease.
The winter of 2003 will be critical for observing how the virus behaves,
whether the winter climate accelerates the transmission, and how we handle
that acceleration. Despite current global efforts, thin lines of transmissions
may remain in China; the virus may flare up again. Officials in China
and sites of the outbreak must interrupt as many chains of transmission
as possible before October. Surveillance should also be intensified. Ongoing
study to improve laboratory diagnosis and clinical virology is key, so
that effective isolation can be practiced; at present, these measures
are the only ones known to interrupt the transmission of SARS. The group
on which to focus should be the community in close contact with previous
outbreak areas.
References
- Imanishi K. A Japanese view of nature: the world of
living things. New York: Routledge Curzon; 2002.
- Ksiazek TG, Erdman D, Goldsmith CS, Zaki SR, Peret T, Emery S,
et al. A
novel coronavirus associated with severe acute respiratory syndrome.
N Engl J Med 2003;348:1953–66.
- Update:
Severe acute respiratory syndrome—United States, June 11, 2003.
MMWR Morb Mortal Wkly Rep 2003;52:550.
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