ARTICLESClinical progression and viral load in a community outbreak ofcoronavirus-associated SARS pneumonia: a prospective study
J S M Peiris, C M Chu, V C C Cheng, K S Chan, I F N Hung, L L M Poon, K I Law, B S F Tang, T Y W Hon, C S Chan, K H Chan,J S C Ng, B J Zheng, W L Ng, R W M Lai, Y Guan, K Y Yuen, and members of the HKU/UCH SARS Study Group*

Summary
Background We investigated the temporal progression of theclinical, radiological, and virological changes in a community
outbreak of severe acute respiratory syndrome (SARS).
Methods We followed up 75 patients for 3 weeks managedwith a standard treatment protocol of ribavirin andcorticosteroids, and assessed the pattern of clinical disease,viral load, risk factors for poor clinical outcome, and theusefulness of virological diagnostic methods.
Findings Fever and pneumonia initially improved but 64 (85%)
patients developed recurrent fever after a mean of 8·9 (SD 3·1)
days, 55 (73%) had watery diarrhoea after 7·5 (2·3) days, 60(80%) had radiological worsening after 7·4 (2·2) days, andrespiratory symptoms worsened in 34 (45%) after 8·6 (3·0)
days. In 34 (45%) patients, improvement of initial pulmonary
lesions was associated with appearance of new radiologicallesions at other sites. Nine (12%) patients developed
spontaneous pneumomediastinum and 15 (20%) developed
acute respiratory distress syndrome (ARDS) in week 3.
Quantitative reverse-transcriptase (RT) PCR of nasopharyngeal
aspirates in 14 patients (four with ARDS) showed peak viralload at day 10, and at day 15 a load lower than at admission.
Age and chronic hepatitis B virus infection treated withlamivudine were independent significant risk factors for
progression to ARDS (p=0·001). SARS-associated coronavirus
in faeces was seen on RT-PCR in 65 (97%) of 67 patients at
day 14. The mean time to seroconversion was 20 days.
Interpretation The consistent clinical progression, shifting
radiological infiltrates, and an inverted V viral-load profile
suggest that worsening in week 2 is unrelated to uncontrolled
viral replication but may be related to immunopathologicaldamage.
Published online May 9, 2003
http://image.thelancet.com/extras/03art4432web.pdf*Members listed at end of paper
Departments of Microbiology and Medicine, Queen Mary Hospital,
University of Hong Kong, Hong Kong, Special Administrative
Region, China (Prof J S M Peiris DPhil, V C C Cheng MRCP,I F N Hung MRCP, L L M Poon DPhil, B S F Tang MB, K H Chan PhD,Y Guan PhD, B J Zheng PhD, Prof K Y Yuen MD); Department ofMedicine, Intensive Care, Radiology, and Pathology, United
Christian Hospital, Hong Kong (C M Chu MRCP, K S Chan FRCP,K I Law MRCP, T Y W Hon FRCP, C S Chan FRCP, J S C Ng MB,
W L Ng MRCP, R W M Lai FRCPA)
Correspondence to: Prof K Y Yuen, Department of Microbiology,
University of Hong Kong, Queen Mary Hospital, Pokfulam Road,
Hong Kong, Special Administrative Region, China(e-mail: kyyuen@hkucc.hku.hk)

Introduction
Severe acute respiratory syndrome (SARS) is a new
emerging disease that has affected many countries, withmore than 3500 cases reported. A novel virus, the SARSassociated coronavirus, has been identified as the causal
agent.1–4 The clinical, radiological, and other investigative
findings at initial presentation have been previously
described,5–7 but the temporal progression is unclear. The
routes and duration of viral shedding and the best clinicalsamples for diagnosis at different stages of the illness arealso largely unknown. From March 24, 2003, a major
outbreak of SARS involving 321 patients occurred inAmoy Gardens, a high-rise housing estate in Hong Kong.
Epidemiological investigations suggested a point-source
outbreak, which was linked to a faulty sewage system,
initially contaminated by the excreta of the index case who
visited the housing block on March 14 and 19.8 The first
75 adult patients, belonging to 57 households, wereadmitted with a clinical diagnosis of SARS to one
hospital. We did a prospective study on the clinical,
haematological, radiological, and microbiological findingsof these 75 patients over a period of 24 days, andcorrelated these findings with treatment9,10 and with viralload in the nasopharyngeal aspirate to elucidate thepathogenesis and the impact of treatment. We report theusefulness of different clinical samples for virologicaldiagnosis and its importance in transmission.

Patients and methods
Patients
Between March 24 and 28, 2003, we included 75 patients
admitted to the United Christian Hospital from the Amoy
Gardens housing estate who fulfilled the modified WHO
definition of SARS.3 Briefly, the case definition is: fever
38ºC or higher, cough or shortness of breath, newpulmonary infiltrates on chest radiography or highresolution CT in the absence of an alternative diagnosis toexplain the clinical presentation. Patients were nursed in
an isolation ward with other SARS patients.
Methods
The study was approved by the ethics committee of theUnited Christian Hospital, Hong Kong. We entered on apredesigned database the daily clinical findings based on
history and physical examination, oximetric measurement, and haematological, biochemical, radiological,
and microbiological investigations. We collected
nasopharyngeal aspirates and clotted blood for virologicalstudies from all patients at presentation and on day 14
after the onset of illnesses. Anteroposterior chest
radiography was done daily for each patient. All chest
radiographs were jointly reported by specialist radiologists
and respiratory physicians. We did high-resolution CT ofthe thorax for patients who had apparently normal,
equivocal, or atypical chest radiographs. For patients whodeveloped acute respiratory distress syndrome (ARDS)
with partial arterial pressure of oxygen (PaO2) to fractionof inspired oxygen (FiO2) less than 26·6 kPa,11 andrecorded acute physiology and chronic health evaluation
II (APACHE II) scores.12

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Temperature (average over 3 days)
Onset of diarrhoea

ARDS requiring intubation

30
25
20
15
10
5

36·5
36·0

Number of new patients

Temperature (°C)

Onset of desaturation

40·0
39·5
39·0
38·5
38·0
37·5
37·0

0
3
1–

6
4–

9
12
15
18
21
24
7– 10– 13– 16– 19– 22–

Time after onset of symptoms (days)
Figure 1: Temporal clinical profiles in 75 patients with SARS
Mean (SD) are presented.

From 20 patients in whom SARS-associated coronavirus
RNA was detected by reverse-transcriptase (RT) PCR in
the initial nasopharyngeal aspirate samples, we collectedfurther nasopharyngeal aspirates, urine, and faecal samples
every 3 days. In 14 of these patients, quantitative PCR wasdone on the nasopharyngeal aspirates collected on days 5,
10, and 15 after onset of symptoms. The nasopharyngeal

aspirates on admission were assessed by rapid
immunofluorescent antigen detection for influenza A and B,
parainfluenza types 1, 2, and 3, respiratory syncytial virus,
and adenovirus, and were cultured for conventional
respiratory pathogens on Mardin Darby Canine Kidney,
LLC-Mk2, RDE, Hep-2, MRC-5, and fetal rhesus kidney(FRhK-4) cell lines. RT-PCR for SARS coronavirus wasdone directly on all clinical samples. Briefly, total RNA fromclinical samples was reverse transcribed with random
hexamers and cDNA was amplified with primers
5TACACACCTCAGCGTTG-3 and 5-CACGAACGTGACGAAT-3.3 For real-time quantitative PCR assays,
cDNA was amplified in an SYBR Green I fluorescence
reactions (Roche, Mannheim, Germany) as described.13
Briefly, 20 L reaction mixtures containing 2 L cDNA,
3·5 mmol/L magnesium chloride, and 0·25 mol/L of thesame forward and reversed primers as the reaction mixtures
were thermal-cycled by a Light cycler (Roche, Mannheim;
95ºC, 10 min followed by 50 cycles of 95ºC, 10 min; 57ºC,
5 s; 72ºC, 9 s). Plasmids with the target sequence were used
to generate the standard curve. At the end of the assay, PCR
products (182 bp) were subjected to a melting curve analysis(65–95ºC, 0·1ºC/s) to find out the specificity of the assay.
The acute and convalescent sera were tested in parallel for
SARS-associated coronavirus IgG, with SARS-associatedcoronavirus-infected Vero cells fixed in acetone in an
indirect immunofluorescent format.

Figure 2: Chest radiographs and high-resolution CT scans from two SARS patients
A Man aged 34 years admitted for high fever and cough. A: Consolidation seen in left upper and middle zones, which progressed maximally at day 7. B: At
day 20, resolution of consolidation in the left upper and middle zones but new widespread air-space opacities noted; those in left lung base wereconfluent. Man aged 32 years, presented with fever, chills, rigors and myalgia, with clear chest radiograph at admission. C: High-resolution CT of thorax
shows peripheral subpleural consolidation in medial basal segment of left lower lobe. D: Resolution of original left lower-lobe consolidation at day 18. E:
Disease complicated by spontaneous pneumomediastinum.

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We investigated blood, sputum or endotracheal aspirates,
and urine bacteriologically, as clinically indicated. All
patients had sepsis work up on admission and if feverrecurred. Stools were sent for routine bacteriologicalculture, Clostridium difficile cytotoxin assay, and examinedfor parasites in selected patients.
All patients were treated with 1·2 g intravenous
amoxicillin-clavulanate every 8 h, and 500 mg oralazithromycin daily. In patients with a known penicillin
allergy, we administered 500 mg oral levofloxacin every
24 h. As soon as the diagnosis of SARS was established,
8 mg/kg intravenous ribavirin every 8 h for 14 days, and atailing regimen of hydrocortisone (starting dose 200 mg
intravenously every 8 h) over 10 days, followed by oral
prednisolone for 11 days (1 mg/kg for 5 days, 0·5 mg/kg for
3 days, and 0·25 mg/kg for 3 days) were given. We usedpulses of methylprednisolone 500 mg intravenously daily for
two or three doses if patients worsened, with increasing
shortness of breath, oxygen desaturation, and radiologicalworsening. All HBsAg-positive patients were given 100 mg
oral lamivudine daily while taking corticosteroids.
Statistical analysis
We compared risk factors associated with the developmentof ARDS by Fisher’s exact test for categorical variables andStudent’s t test for continuous variables. Significant risk
factors identified on univariate analyses were further
analysed by multiple logistic regressions to identify
independent risk factors associated with the development of
ARDS. We took p<0·05 to be significant. We used SPSS(version 11.0) for all analyses.
Role of the funding source
The sponsors of the study had no role in the study design,
data collection, data analysis, data interpretation, or in thewriting of the report.

patients, respectively. The median lymphocyte counts
decreased from 0·8109/L (IQR 0·6–1·1) on admission to
0·6109/L (0·5–0·9), 0·4109/L (0·3–0·5), and 0·4109/L(0·3–0·6) at days 7, 14, and 21, respectively.
In terms of disease progression, all except one patient
became afebrile within 48 h with the standard treatment
protocol, but the fever recurred in 64 (85%) patients at amean of 8·9 days (SD 3·1). Only ten of these patients had
positive findings on sepsis work up: three had
Stenotrophomonas maltophilia bacteraemia, four had clinicalevidence of catheter-related sepsis, and three had
nosocomial pneumonia due to Klebsiella pneumoniae (in two)and Escherichia coli (one). All these septic episodes
responded to the appropriate antimicrobial treatment andremoval of infected catheters. In the remaining 54 patients,
fever recurred after a mean of 8·0 (2·1) days, which was
unlikely to be caused by hospital-acquired infection.
Between days 13 and 15, 17 (23%) patients developed
another episode of fever (figure 1).
Watery diarrhoea developed in 55 (73%) patients, withonset at a mean of 7·5 (2·3) days. The rate of diarrhoea
peaked at a mean of 8·7 (2·3) days, with a maximum
frequency of 6·3 (3·5) times daily (figure 1). Work up for
diarrhoeal pathogens, including C difficile cytotoxin, wasnegative in all these patients. The mean duration ofdiarrhoea was 3·9 (2·3) days. Simultaneous occurrence offever and diarrhoea occurred in 24 (32%) patients.
Concomitant fever, diarrhoea, and radiological worsening
occurred in 16 (21%) patients. Improvement of diarrhoea
occurred in all patients by day 13.
Radiological worsening was noted in 60 (80%) patientsat a mean of 7·4 (2·2) days: 34 (45%) developed shifting ofradiological lesions, evidenced by improvement of original
lesions followed by the appearance of new lesions(figure 2); worsening of original lesions with or without
ARDS(n=15)

Results
Of the 75 patients, 71 (95%) were ethnic Chinese, and theremainder were Filipino. The male-to-female ratio was one
to 0·92, and mean age was 39·8 (SD 12·2) years. Five
patients were smokers. Underlying diseases were identified
in 13 patients, including nine patients positive for HBsAg
with no stigmata of chronic liver disease and normal liverfunction tests. The clinical symptoms on admission
included fever in 75 (100%) patients, chills in 49 (65%),
rigors in 42 (56%), myalgia in 51 (68%), cough in 22(29%), sore throat in eight (11%), shortness of breath in
three (4%), headache in 11 (15%), dizziness in three (4%),
and diarrhoea in one (1%).
Initial chest radiograph was abnormal in 53 (71%)
patients; involvement was confined to one lung zone in 37(49%) and was multizonal in 16 (21%). Lower-zone
infiltrates or consolidation occurred in 45 (60%) patients.
Initial high-resolution CT was done in 33 (44%) patients inwhom the initial chest radiographs were normal, equivocal,
or atypical. Of these 33 patients, 18 (55%) had
abnormalities confined to one lobe. Multilobar involvement
was seen in 15 (46%) patients. Focal ground-glass
opacification was the only type of abnormality in eight(24%) patients. 12 (36%) patients had consolidation only,
and 13 (39%) had both types of infiltrates.
On haematological and biochemical investigation,
anaemia was detected in six (8%), leucopenia in five (7%),
severe lymphopenia of less than 1109/L in 56 (75%), andthrombocytopenia in 28 (37%). Raised values were seen foralanine aminotransferase (42–343 U/L), aspartate
aminotransferase (39–302 U/L), and creatinine kinase(176–1466 U/L) in 22 (29%), 24 (32%), and 27 (36%)

Mean (SD) age (years)
Male/female ratio
Underlying illnesses
Chronic hepatitis B virus infection
Mean (SD) duration of symptoms
to admission (days)
Mean (SD) initial haemoglobin
concentration (g/L)
Mean (SD) initial total peripheral
white blood cell count (109/L)
Mean (SD) initial lymphocyte
count (109/L)
Mean (SD) initial platelet
count (109/L)
Mean (SD) initial creatinine(mol/L)
Mean (SD) initial ALT (U/L)
Mean (SD) initial CPK
Mean (SD) initial LDH
NPA RT-PCR positive at diagnosis
Mean (SD) day of antibody
seroconversion after onsetof symptoms
Apparently normal chest
radiograph on admission‡Multilobar involvement on chest
radiograph on admission
Diarrhoea
Recurrent fever

No ARDS(n=60)

p

48·5 (12·6)
11/4
9 (60%)*
6 (40%)
2·6 (1·1)

37·3 (11·3) 0·002
25/35
0·042
4 (7%)<0·001†
3 (5%)
0·001
2·38 (1·2) 0·51

135 (21)134 (12)0·79

7·1 (2·1)

6·1 (2·1)

0·09

1·1 (0·9)

0·9 (0·4)

0·19

163 (56)

167 (41)0·77

94·5 (11·1)

86·1 (14·6)

0·004

47·8 (27·5)
35·9 (45·2)
327·1 (367·7) 161·5 (125·9)
482·6 (242·9) 384·8 (119·8)
5 (33%)
19 (31·7%)
20·0 (5·5)
19·9 (4·9)

0·33
0·11
0·25
0·77
0·94

4 (27%)

18 (30%)1·05 (33%)

11 (18%)0·29

12 (80%)13 (87%)43 (72%)41 (68%)

0·75
0·21

ALT=alanine aminotransferase. CPK=creatinine phosphokinase. LDH=lactic
dehydrogenase. NPA=nasopharyngeal aspirate. *Three patients had chronic active
hepatitis B, one had uterine fibroid. †SARS established by clinical features plus
high-resolution CT findings. ‡Six patients had chronic active hepatitis B infection,
one had carcinoma of ovary, one had diabetes mellitus, and one had asthma.

Table 1: Risk factors associated with development of ARDS
requiring ventilatory support and intensive care

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Adjusted odds ratio (95% CI) p
Independent predictive factors
Age-groups (years)
21–40
41–60
61–80
HBsAg-positive patients

1·0
4·3 (0·9–20·0)
28·0 (3·1–253·3)
18·0 (3·2–101·3)

··
0·06
0·003
0·001

Table 2: Independent risk factors predicting development of
ARDS by multivariate analysis

n=75
OutcomeDeath*
Convalescence at home or at rehabilitation facility
Transfer to special obstetric unit
Hospital admission
In general ward
In intensive-care unit for ARDS

5 (7%)
27 (36%)
1 (1%)
29 (39%)13 (17%)*Two patients died of acute myocardial infarction, one of clinical sepsis, and twoof clinical sepsis and ARDS

Table 3: Outcomes in SARS patients at the time of writing

Cumulative proportion of patients with seroconversion (%)

development of new lesions was noted in the remaining
26 (35%) patients. Overall, 46 (61%) patients subsequently
in 70 (93%) patients at mean of 20 (5·1) days (figure 3).
improved, 11 (15%) had remained static at the time of
SARS-associated coronavirus RNA was detected inwriting, and 18 (24%) further progressed into a diffuse
nasopharyngeal aspirates by RT-PCR in 24 (32%) ofground-glass appearance at a mean of 12·0 (4·4) days. Of
75 patients at initial presentation (mean 3·2 [1·3] days after
the 18 patients with diffuse ground-glass changes, 15
onset) and in 51 (68%) at day 14. In stool samples collecteddeveloped ARDS. Among all 75 patients, nine (12%)
later in the illness (a mean of 14·2 [2·2] days after onset),developed spontaneous pneumomediastinum during
viral RNA was detected in 65 (97%) of 67. Similarly, viralfollow-up. The characteristic shifting of radiological
RNA was detected in 31 (42%) of 74 urine samples
changes is illustrated in figure 2.
collected at a mean of 15·2 (1·7) days after onset of
33 (44%) patients developed arterial oxygen desaturation
symptoms.
of less than 90% at room air, at a mean of 9·1 (4·2) days
The 20 patients initially documented to have SARSafter onset of symptoms (figure 1). 24 (32%) patientsassociated coronavirus RNA in the nasopharyngeal aspirates
required intensive care at a mean of 11·0 (6·4) days, amongon RT-PCR were serially followed up with sequential
whom 19 had to be intubated at a mean of 12·9 (6·4) days.
samples; the virological profile is shown in table 4.
15 (20%) patients progressed to ARDS and required
Quantitative RT-PCR of the nasopharyngeal aspirates
mechanical ventilation. On day 1 of mechanical ventilation
showed an inverted V pattern, with mean geometric viralfor ARDS, the mean PaO2-to-FiO2 ratio was 14·7 kPa
loads of 2·3105 copies per mL, and 1·9107 copies per(10·8) and the mean APACHE II score was 22·3 (5·8).
mL, and 9·8104 copies per mL on days 5, 10, and 15,
Time to occurrence of ARDS showed a bimodal pattern,
respectively, after onset of symptoms (figure 4).
with one peak at 11·0 days and another peak at 20·0 days
(figure 1). Seven patients developed hospital-acquired
Discussion
infection during their stay in the intensive-care unit,
Studies on SARS have generally been retrospective or
including hospital-acquired pneumonia in three, meticillinlimited to the description of the initial clinical,
resistant Staphylococcus epidermidis bacteraemia in one, andhaematological, radiological and microbiological findings.
clinical sepsis in three, without positive cultures.
The patients we studied, however, were residents of a
On univariate analysis, the risk factors associated withhousing estate placed under closed surveillance by the
ARDS requiring ventilatory support and intensive care were
Department of Health soon after identification of theage, male sex, chronic hepatitis B virus carriage, raised
outbreak. All residents underwent frequent health checks,
creatinine, and recurrence of fever (table 1). Lymphocyte
and symptomatic patients were admitted to hospital soon
counts of ARDS patients on days 7, 14,
and 21 did not differ significantly from100
those in non-ARDS patients. On
multivariate analysis, only age and90
chronic hepatitis B virus infection weresignificant risk factors (table 2).
80
The mean length of stay for
75 patients was 22·1 (3·1) days, whereas
70
for the 15 patients who developed
ARDS, the mean length of stay was
26·8 days at the time of writing. Five60
patients died during the study period, ofwhom two, aged 79 and 64 years, had
50
succumbed to acute myocardial
infarction on days 13 and 17,
40
respectively. One patient died of clinicalsepsis on day 23. Another two patients
30
died of clinical sepsis and ARDS on
days 24 and 25, respectively. 27 (36%)
20
of patients were discharged home ortransferred to a rehabilitation facility.
One patient was transferred to a
10
specialised obstetric unit for urgent
delivery of a baby at 32 weeks’0gestation. For the 42 patients who
10 12 14
16 18 20
22 24 26 28 30
0
2
4
6
8
remained in the hospital, 13 wereTime after onset of symptoms (days)
treated in intensive care for ARDS
(table 3).
Figure 3: Kinetics of IgG seroconversion to SARS-associated coronavirus
IgG seroconversion was documented Cumulative data on earliest time to seroconversion is presented.

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Time after onset of symptoms (days; n=20)

Sample (positivity rate)
Nasopharyngeal aspirate
Stool
Urine

10

13

16

19

21

19 (95%)20 (100%)
10 (50%)18 (90%)20 (100%)
9 (45%)

18 (90%)19 (95%)7 (35%)

15 (75%)12 (80%)†6 (30%)

9 (47%)*
10 (67%)†4 (21%)**In 19 patients. †In 15 patients

Table 4: Subsequent analysis of clinical samples of 20 patients with initial RT-PCR-positive nasopharyngeal aspirates and antibody
seroconversion to SARS-associated coronavirus

20 patients who underwent prospective follow-up with RTPCR. Taken together, these findings suggest that the lungdamage at this phase is related to immunopathologicaldamage as a result of an overexuberant host response, rather
than uncontrolled viral replication. 20% of patients in thiscohort progressed to the third phase, characterised by
ARDS necessitating ventilatory support. Inevitably, several
patients developed nosocomial sepsis during this phase of
end-organ damage and severe lymphopenia.
In terms of pathogenesis, in pulmonary reovirus infection
in athymic mice, a lower plaque-forming value of 106 is
associated with pathological changes of bronchiolitis
obliterans organising pneumonia, whereas a higher
inoculum of 107 is associated with ARDS.14 To lessen therisk of progression to the chronic phase of ARDS, aneffective antiviral to reduce the viral load may be important.
At the time of writing, no antiviral is reported to be clinicallyeffective for the treatment of this novel coronavirus.
Ribavirin has broad-spectrum antiviral activities and iseffective for the treatment of fulminant hepatitis in micecaused by the mouse hepatitis coronavirus.15 Although the
inhibitory activity of ribavirin against mouse hepatitis
coronavirus is weak, ribavirin can decrease the release ofproinflammatory cytokines from the macrophages of mice.
It also switched the immune response of the mice from a Thelper-2 to a T-helper-1 response. Thus, irrespective of its
antiviral role, ribavirin may act as an
Patient A
Patient H
immunomodulator.
Aneffective
Patient B
Patient I
antiviral agent is needed because
Patient C
Patient J
decreasing the initial cytolytic damage
Patient D
Patient K
and viral load in the first phase may inPatient E
Patient L
turn result in decreased immuno9
Patient F
Patient M
pathological damage during thePatient G
Patient N
second phase. Since a notableproportion of our patients developed
8
ARDS, the role of immunologicallydirectedstrategies,
suchas
corticosteroids,
intravenous
immuno7
globulin, IgM-enriched immunoglobulin, convalescent plasma, andthe antitumour necrosis factor thy6
mosin, deserve further investigation.
Unexpectedly, chronic hepatitis B
infectionwasanimportant5
independentrisk
factorfor
progression to ARDS. This finding
may also explain a higher rate of death4
among young Chinese patients
because of the high rate of chronic
hepatitis B infection in Southern
3
China. The finding is importantbecause in all our patients, lamivudine
was given as prophylaxis while the2patients were taking corticosteroids.
0
5
10
15
20
We did not assess the viral load forTime after onset of symptoms (days)
hepatitis B virus DNA since the liverfunction tests were normal with no
Figure 4: Sequential quantitative RT-PCR for SARS-associated coronavirus inclinical stigmata of chronic liver
nasopharyngeal aspirates of 14 SARS patients
diseases. Thus these patients’ poor
Log10 copies/mL nasopharyngeal aspirate

after the onset of symptoms and, thus, were admitted earlyin the course of the illness. Therefore, we were able to do aprospective study in a large cohort of patients infected in
one community outbreak of SARS who were
epidemiologically linked, and of whom most had
virologically confirmed SARS-associated coronavirus.
The clinical progression of SARS was mostly uniform inour cohort, with a tri-phasic pattern. Week 1 wascharacterised by fever, myalgia, and other systemic
symptoms that generally improve after a few days. The
increasing viral load during this phase suggests that thesymptoms are largely related to the effect of viral replicationand cytolysis. As the disease progressed into week 2, thepatients frequently had recurrence of fever, onset of
diarrhoea, and oxygen desaturation. Strikingly, nearly half
the patients had shifting radiographic shadows. If viralinduced damage was the primary pathological mechanism,
such a flitting pattern of radiological change is difficult to
explain. The timing of the IgG seroconversion, which starts
on day 10, seems to correlate with falls in viral load, which
occurs from between day 10 and 15, despite the use of pulse
methylprednisolone. Severe clinical worsening also occurs at
this time, which cannot be explained by uncontrolled viral
replication. This finding is supported by the progressive
decrease in rates of viral shedding from nasopharynx, stool,and urine from day 10 to 21 after onset of symptoms in the

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outcome cannot be explained by uncontrolled hepatitis
activity. An unknown immune defect in chronic hepatitis B
carriers may account for their poor ability to control thecoronavirus infection or the associated immunopathologicaldamage. Co-infection with SARS coronavirus in hepatitis B
carriers may predict a worse prognosis. The option ofprophylaxis with intranasal interferon alfa could be
investigated in household contacts and health-care workers,
especially in those with chronic hepatitis B virus carriage,
because this approach is effective in other humancoronavirus infections.16
The case definition of SARS is clinical and rather nonspecific in the absence of epidemiological history of contact.
We showed that IgG seroconversion has 93% sensitivity at
day 28, even despite corticosteroid treatment. In this case,
IgG isotype-specific antibody to the SARS coronavirus wastested for. If antibody to all immunoglobulin classes is
assayed for, seroconversion will probably be detected earlier.
Although viral RNA detection in the nasopharyngeal
aspirate has a sensitivity of only 32% at presentation, testingof multiple nasopharyngeal and faecal samples increased thesensitivity of the RT-PCR assay.
The presence of virus in the stool is an important finding
because it suggests the possibility of oral-faecal
transmission. The epidemiological investigation of theAmoy Gardens SARS outbreak suggested that the outbreak
was caused by a faulty sewage system.8 Diarrhoea seemed
more prominent in our cohort of patients than previously
reported,3,7 and the severe watery diarrhoea in these patients
presented a challenge to health-care workers for infection
control. Whether this apparent change in the clinicalpresentation is related to the difference in the route of
infection or a mutation in the virus is still conjectural.
Importantly, the mortality rate of 6·7% we reported ishigher than the previously reported figure of 3·5% at
day 21.6
We noted the absence of a relation between the high rateof spontaneous pneumomediastinum unrelated to
intubation and positive-pressure ventilation. This phenomenon is rarely reported in advanced cytomegalovirus
pneumonia,17 and influenza bronchiolitis,18 whereas
spontaneous pneumothorax is commonly reported inPneumocystis carinii, and Staphylococcus aureus pneumonia.
The initial radiographic lesions in SARS were pleural
based.6 In patients in whom the initial consolidation isabutting on to the mediastinum, adhesions and cyst
formation might occur at the interface between the
mediastinal pleura and the pulmonary pleura. Any ruptureof these cysts will result in spontaneous pneumomediastinum. Alternatively, a diffuse peripheral pneumonicchanges followed by pleural adhesion may occur over theparietal pleura of the chest walls, which leaves themediastinal sites as the area in which rupture of cyst canoccur. This will also create the necessary setting for
spontaneous pneumomediastinum to occur without
spontaneous pneumothorax.
RT-PCR on respiratory and faecal samples, together withserology, can confirm the diagnosis of SARS-associatedcoronavirus infection in most SARS patients. The
progression of the disease to respiratory failure might not be
associated with uncontrolled viral replication, but may, infact, be immunopathological in nature.
Contributors
J S M Peiris and K Y Yuen are co-principal investigators, jointly wrote thereport, and supervised the virological and clinical component of the study.
C M Chu, V C C Cheng, K S Chan, I F N Hung, K I Law, B Y F Tang,J S C Ng, and W L Ng were involved in collection and analysis of the clinicaldata. C S Chan and T Y W Hon were involved in radiological analysis.
L L M Poon, K H Chan, and Y Guan did the quantitative PCR and other6

virology assays. R W M Lai coordinated the microbiological investigations in
United Christian Hospital.

Members of the HKU/UCH SARS Study GroupS W Kwan, K F Lo, A M Y Fung, I M T Chu, W T Hui, H K Leung,W H Seto, Department of Microbiology, Queen Mary Hospital; S Y Lam,P C Y Woo, S K P Lau, W Luk, H Y Ng, L J Zhang, C Y Cheung,
O K Wong, W Cheung, G Tse, Department of Microbiology, University ofHong Kong; P W Ng, T C Sim, L S Lau, V Chan, W S Leung,
J T M Chan, K L Lee, Y S Poon, E Chow, C Y Leung, F L Lau, W L Tsoi,A C H Choi, C N C Chan, M F Leung, C Y Tse, United Christian
Hospital.

Conflict of Interest statement
None declared.

Acknowledgments
We thank E K Yeoh of the Hong Kong Government for facilitating thisstudy; Klaus Stöhr and WHO for initiating and coordinating the informationexchange between members of the WHO SARS Laboratories network; andthe staff of the Department of Microbiology, Queen Mary Hospital, and of
the Department of Medicine and Intensive Care Unit, United Christian
Hospital, for technical assistance and management of patients. Researchfunding was received from from the National Institute of Allergy and
Infectious Diseases, USA (public health research grant A195357), theWellcome Trust (grant GR067072/D/02/Z), University of Hong Kong andthe Hospital Authority of Hong Kong.

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