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Dispatch
Severe Acute Respiratory Syndrome–associated
Coronavirus Infection
Paul K.S. Chan,* Margaret Ip,* K.C. Ng,* Rickjason C. W. Chan,* Alan
Wu,* Nelson Lee,* Timothy H. Rainer,* Gavin M. Joynt,* Joseph J. Y. Sung,*
and John S. Tam*
*The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin,
Hong Kong
Suggested citation
for this article:
Chan PKS, Ip M, Ng KC, Chan RCW, Wu A, et al. Severe acute respiratory
syndrome-associated coronavirus infection. Emerg Infect Dis [serial
online] 2003 Nov [date cited]. Available from: URL: http://www.cdc.gov/ncidod/EID/vol9no11/03-0421.htm
Whether severe acute
respiratory syndrome–associated coronavirus (SARS-CoV) infection can
be asymptomatic is unclear. We examined the seroprevalence of SARS-CoV
among 674 healthcare workers from a hospital in which a SARS outbreak
had occurred. A total of 353 (52%) experienced mild self-limiting illnesses,
and 321 (48%) were asymptomatic throughout the course of these observations.
None of these healthcare workers had antibody to SARS CoV, indicating
that subclinical or mild infection attributable to SARS-CoV in adults
is rare.
The outbreak of severe acute respiratory syndrome (SARS) at the Prince
of Wales Hospital, Hong Kong, began on March 10, 2003 (1,2).
Within the next 10 weeks, the hospital admitted 331 patients with SARS;
160 (48.3%) were healthcare workers (HCWs). Prince of Wales is a 1,350-bed
teaching hospital with 3,711 employees, of whom 12% are physicians, 36%
nurses, 11% allied health workers, and the remainder, administrative and
ancillary staff. During the outbreak, many HCWs had been exposed directly
or indirectly to aerosols, body fluids, secretions, and excretions of
SARS patients. The clinical manifestations of SARS are well documented
(2–5). However, we do not yet know the spectrum of clinical
disease or whether mild or asymptomatic infections attributable to the
SARS-associated coronavirus (SARS-CoV) occur. Whether subclinical infections
occur and whether one may seroconvert to the SARS-CoV with minimal or
no symptoms are concerns for HCWs and others.
The Study
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![Figure.](images/03-0421_t.gif) |
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enlarged image
Figure. Number of patients with severe acute
respiratory syndrome (SARS) admitted to Prince of Wales Hospital
during the first 10 weeks of the SARS outbreak...
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We performed a prospective study to determine whether asymptomatic or
mild infection attributable to SARS-CoV was common in HCWs in this outbreak
at Prince of Wales Hospital. When it had been established that an outbreak
was occurring, a SARS screening clinic was instituted to care for hospital
staff with symptoms suggestive of or suspected to be SARS. Asymptomatic
staff or those without compatible symptoms were also invited to participate
in this study. In late March and early April 2003, a blood sample was
collected from each HCW who voluntarily participated and who wished to
be tested for antibody to SARS-CoV; a second blood sample was collected
4–6 weeks later. Most of the second blood samples were collected in early
May 2003, approximately 8 weeks from the first peak and 4 weeks from the
second peak of admission of HCWs with SARS (Figure).
Each HCW completed a questionnaire to document known direct contact with
SARS patients, their body fluids, secretions, or excretions; places of
duty within the hospital; and symptoms of any illness during the period
between first and second blood sample collection. Additional information
also included the department and the position of HCWs, so that the job
nature could be delineated.
Immunoglobulin (Ig) G antibody to SARS-CoV was detected by an immunofluorescence
assay on the basis of Vero cells infected with coronavirus isolated from
a patient with SARS. We isolated this SARS-CoV and determined the complete
genome sequence (GenBank accession no. AY278554). Serum samples were diluted
1:40 for antibody-screening assays. Each result was crosschecked by two
experienced technicians. This immunofluorescence assay had been successfully
used for serodiagnosis of SARS in patients in our hospital; titers of
>320 developed in acutely ill SARS patients 4 weeks after onset of
illness.
Conclusions
Six hundred and seventy-four HCWs completed the questionnaire and had
a second serum sample obtained. The mean age of these HCWs was 40 years
(range 20–60), and 75% were female. HCW jobs were categorized into five
groups according to those with direct patient care, namely: doctors and
nurses, 28% (188); healthcare and general service assistants, 15% (104);
and allied health workers, including physiotherapists, occupational therapists,
and x-ray technicians, 6% (43). The remainder of staff, who did not have
direct patient care, included the ancillary staff, 35% (235); pathology
laboratory staff, 14% (95); and others, 1% (9 HCWs). Altogether, 43% of
the HCWs reported having known direct contact with patients with SARS
or their body fluids, secretions, or excretions. An additional proportion
of HCWs might have had contact with patients who subsequently were confirmed
to have had SARS, unknown to the HCWs. A total of 36% of the staff worked
in or visited adult medical or pediatric wards with SARS patients—30%
in the accident and emergency unit and 9% in the intensive-care unit—all
areas at high risk for SARS within the hospital during the outbreak. Of
the 674 HCWs, 353 (52%) reported mild, self-limiting illnesses during
the period between the times when the first and second blood samples were
collected (Table). None of the 674 HCWs was shown
to have IgG antibody to SARS CoV.
The current global outbreak of SARS is associated with a novel coronavirus,
SARS-CoV, which is phylogenetically distinct from other known members
of the virus family (Coronaviridae) and genus (Coronavirus)
(6–8). The full clinical spectrum of this novel infection
in humans has not yet been defined. Among the 674 HCWs that we examined,
none showed evidence of seroconversion to SARS-CoV.
It is possible that a proportion of our study participants might not
have actually been exposed to SARS-CoV. Although these participants were
working in our hospital when a large number of patients with SARS were
staying there, vigilant infection-control measures had been in place since
the outbreak was recognized (9). All staff working in
high-risk areas were required to wear a mask, gloves, eye goggles, and
protective clothing. These measures have been shown to reduce the risk
for infection (10).
The results of this study show that our SARS clinic successfully identified
all staff with SARS-CoV infections. Alternatively, our data suggest that
asymptomatic or mild forms of SARS-CoV are rare at the current point to
which the virus has evolved. From the virologic viewpoint, this finding
indicates that the novel coronavirus has not yet adapted to transmit among
humans through asymptomatically infected hosts. This finding has important
public health implications, as the level of immunity towards SARS-CoV
could be very low even in members of communities that had had a large
outbreak of SARS. If this is the case, a large proportion of the population
remains susceptible, and another major outbreak may occur when the virus
is introduced by highly infectious sources.
Acknowledgments
We express our appreciation
to all healthcare workers in Hong Kong Special Administrative Region
who have cared for patients with severe acute respiratory syndrome.
Dr. Paul Chan is
a clinical virologist and associate professor at the Department of Microbiology,
Faculty of Medicine, the Chinese University of Hong Kong. His research
interests include emerging viral infections, viral epidemiology, diagnostic
virology, and viral oncology.
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Table.
Symptoms reported by healthcare workers without SARS-CoV infectiona |
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Symptomb
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No. (%) of healthcare workers
N = 353
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Headache
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194 (55.0)
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Sore throat
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174 (49.3)
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Cough
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140 (39.7)
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Coryza
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139 (39.4)
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Sputum
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87 (24.6)
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Myalgia
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83 (23.5)
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Diarrhea
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80 (22.7)
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Dizziness
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75 (21.2)
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Chills/rigors
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69 (19.5)
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Fever
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68 (19.3)
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aSARS-CoV, severe
acute respiratory syndrome–associated coronavirus. |
bAll symptoms reported
were mild, self-limiting, and lasted for 1 to 2 days. |
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