Published Date: 2003-03-25 23:50:00
Subject: PRO/EDR> SARS - worldwide (04): etiology
Archive Number: 20030325.0737
SARS - WORLDWIDE (04): ETIOLOGY
A ProMED-mail post
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International Society for Infectious Diseases
Date: 25 Mar 2003
From: ProMED-mail <email@example.com>
Source: CDC Press Release
CDC Lab Analysis Suggests New Coronavirus May Cause SARS
The Centers for Disease Control and Prevention (CDC) announced today that a
previously unrecognized virus from the coronavirus family is the leading
hypothesis for the cause of severe acute respiratory syndrome (SARS). Two
coronaviruses that are known to infect humans cause one third of common
colds and are also a common cause of health care-associated upper
respiratory infections in premature infants.
"This is encouraging news from our laboratories at CDC," said Tommy G.
Thompson, Secretary of Health and Humans Services. "These and other
excellent scientists all over the world have been working around the clock
for days and their hard work is paying off. They continue to look at other
possible causes of SARS, but this is a key finding in our efforts to
identify the cause of this global outbreak."
Additional steps needed to confirm this hypothesis include further
culturing of the virus from appropriate specimens, sequencing the viral
genome, and examining specimens from patients at different stages of their
"This collaboration among scientists led by the World Health Organization
(WHO) is unprecedented," said CDC Director Dr. Julie Gerberding. "We
certainly have more work to do, but we think we are on the right track. And
our systems to identify cases and investigate them are working too, thanks
to all the frontline clinicians and state and local health departments
around the country."
As of Mon, 24 Mar 2003, CDC is reporting 39 suspected SARS cases in 18
states. WHO is reporting 456 cases and 17 deaths.
Since the outbreak of SARS was first reported two weeks ago, CDC has
responded in these ways:
Activated the agency's Emergency Operations Center.
Alerted public health partners in cities and states by issuing electronic
Prepared and distributed more than 60,000 health alert cards to travelers
returning from Southeast Asia.
Provided guidance to public health departments, health care facilities, and
clinicians in monitoring and identifying potential cases.
Provided safe specimen-handling guidelines to laboratories.
Deployed more than a dozen CDC staff members, including medical officers,
epidemiologists, infection control specialists, and pathologists to support
the World Health Organization in the global investigation.
Provided regular media briefings to report on progress of the investigation.
[This report does not provide much clarity but rather adds to the confusion
regarding the nature of the infectious agent responsible for SARS. The
candidates so far include, an unspecified paramyxovirus, the recently
discovered human metapneumovirus (representing the two subfamilies of the
family _Paramyxoviridae_, and now an unspecified coronavirus (representing
the family _Coronaviridae_). A common feature of the families
_Paramyxoviridae_ and Coronaviridae_ is that they contain viruses that are
ubiquitous respiratory tract pathogens. Consequently it would not be
unexpected to detect such viruses in clinical samples entirely
fortuitously, particularly where a diagnostic technique of limited
discriminatory potential such as electron microscopy is employed. The
paramyxoviruses and coronaviruses are quite distinct viruses with different
biological potential. The paramyxoviruses are negative-sense RNA viruses,
which do not recombine, whereas the coronaviruses are positive-sense RNA
viruses, which undergo recombination at high frequency.
In the UK at least coronaviruses are second only to rhinoviruses as causes
of the common cold. In the case of the four types of human parainfluenza
viruses (sub-family _Paramyxovirinae_), human respiratory syncytial virus
and human metapneumovirus (sub-family _Pneumovirinae_) infection occurs in
infancy and early childhood, but does not confer prolonged immunity. In the
case of human respiratory syncytial virus it has been estimated that
reinfection occurs on average every 36 months. The outcome of infection can
be serious in infancy (bronchiolitis) and in the elderly (pneumonia), At
other ages infection is usually asymptomatic or mild URTI. The recently
discovered human metapneumovirus appears to behave similarly, but is less
prevalent than respiratory syncytial virus (see: Human metapneumovirus
infections in young and elderly adults by Falsey et al., in Journal of
Infectious Diseases, 187, (5), 785-790, 2003). These authors conclude that:
"Human metapneumovirus infection occurs in adults of all ages and may
account for a significant portion of persons hospitalized with respiratory
infections during some years."
Continued caution is required in evaluation of the competing claims of
identification of the etiologic agent of SARS. - Mod.CP]