Detection of severe acute respiratory syndrome coronavirus RNA in plasma during the course of infection

We examined severe acute respiratory syndrome-associated coronavirus (SARS-CoV) RNA in plasma of 32 patients (probable SARS cases) by a quantitative real-time reverse transcription-PCR assay and reported that the highest detection rate, 75%, was found between day 5 and day 7 of illness, followed by rates of 64, 50, and 38% found between day 8 and day 11, day 2 and day 4, and day 12 and day 16, respectively. Analysis of sequential SARS-CoV load in plasma from six cases revealed different patterns of viremia, with the peak between day 4 and day 8. Our findings of the high detection rate of SARS-CoV RNA in plasma before day 11, together with the relative convenience of collecting and handling plasma, suggest that plasma can be used for early diagnosis of SARS.

Multiplexed detection of pathogen DNA with DNA-based fluorescence nanobarcodes

Rapid, multiplexed, sensitive and specific molecular detection is of great demand in gene profiling, drug screening, clinical diagnostics and environmental analysis^1,2,3. One of the major challenges in multiplexed analysis is to identify each specific reaction with a distinct label or 'code'⁴. Two encoding strategies are currently used: positional encoding, in which every potential reaction is preassigned a particular position on a solid-phase support such as a DNA microarray^5,6,7,8, and reaction encoding, where every possible reaction is uniquely tagged with a code that is most often optical or particle based^{4,9,10,11,12,13}. The micrometer size, polydispersity, complex fabrication process and nonbiocompatibility of current codes limit their usability^1,4,12. Here we demonstrate the synthesis of dendrimer-like DNA-based, fluorescence-intensity-coded nanobarcodes, which contain a built-in code and a probe for molecular recognition. Their application to multiplexed detection of the DNA of several pathogens is first shown using fluorescence microscopy and dot blotting, and further demonstrated using flow cytometry that resulted in detection that was sensitive (attomole) and rapid.

Study on the resistance of severe acute respiratory syndrome-associated coronavirus

In this study, the persistence of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) was observed in feces, urine and water. In addition, the inactivation of SARS-CoV in wastewater with sodium hypochlorite and chlorine dioxide was also studied. In vitro experiments demonstrated that the virus could only persist for 2 days in hospital wastewater, domestic sewage and dechlorinated tap water, while 3 days in feces, 14 days in PBS and 17 days in urine at 20 degrees C. However, at 4 degrees C, the SARS-CoV could persist for 14 days in wastewater and at least 17 days in feces or urine. SARS-CoV is more susceptible to disinfectants than Escherichia coli and f2 phage. Free chlorine was found to inactivate SARS-CoV better than chlorine dioxide. Free residue chlorine over 0.5 mg/L for chlorine or 2.19 mg/L for chlorine dioxide in wastewater ensures complete inactivation of SARS-CoV while it does not inactivate completely E. coli and f2 phage.

Clinical, virologic and immunologic profiles of a young infant with severe acute respiratory syndrome

The clinical findings, plasma viral load, cytokines and chemokines of a 4-month-old infant with severe acute respiratory syndrome (SARS) were assessed at different phases of the disease. Ribavirin failed to inhibit SARS coronavirus (SARS-CoV) replication. One-step real time reverse transcription-polymerase chain reaction for plasma SARS-CoV RNA quantification was useful for early diagnosis and monitoring viremia.

Persistent shedding of viable SARS-CoV in urine and stool of SARS patients during the convalescent phase

In order to further the present knowledge of the emerging severe acute respiratory syndrome-associated coronavirus (SARS-CoV), 486 different specimens from 54 patients with a clinical diagnosis of SARS were investigated for the presence of viral RNA, and 314 plasma specimens of 73 patients were examined for IgM and IgG antibodies specific against SARS-CoV using an indirect ELISA. Viral RNA was detectable in 28 of the 54 patients tested. Cumulative data showed that 67 of the 73 SARS patients demonstrated seroconversion by week 5 of illness. In contrast, only 1 of 278 healthy subjects enrolled in the study was found to be positive for the IgG antibody. Coexistence of viral RNA in plasma and specific antibodies was simultaneously observed over three consecutive weeks in two critical cases. In three convalescent patients in particular, cultivable SARS-CoV was detected in stool or urine specimens for longer than 4 weeks (29-36 days). These findings suggest that SARS-CoV may remain viable in the excretions of convalescent patients.

Evaluation of modified vaccinia virus Ankara based recombinant SARS vaccine in ferrets

Severe acute respiratory syndrome (SARS) caused by a newly identified coronavirus (SARS-CoV) remains a threat to cause epidemics as evidenced by recent sporadic cases in China. In this communication, we evaluated the efficacy and safety of two SARS vaccine candidates based on the recombinant modified vaccinia Ankara (MVA) expressing SARS-CoV spike or nucleocapsid proteins in ferrets. No clinical signs were observed in all the ferrets challenged with SARS-CoV. On the other hand, vaccination did not prevent SARS-CoV infection in ferrets. In contrast, immunized ferrets (particularly those immunized with rMVA-spike) exhibited significantly stronger inflammatory responses and focal necrosis in liver tissue after SARS-CoV challenge than control animals. Thus, our data suggest that enhanced hepatitis is linked to vaccination with rMVA expressing SARS-CoV antigens.

Genosensor on gold films with enzymatic electrochemical detection of a SARS virus sequence

A hybridisation-based genosensor was designed on a 100 nm sputtered gold film. This material worked as an immobilisation and transduction surface. A 30-mer sequence that encodes a short lysine-rich region, unique to SARS (severe acute respiratory syndrome) virus, was chosen as target. A complementary strand (probe), labelled with a thiol group at the 3'-end, was immobilised on the film. After blocking the surface, hybridisation with the biotin-conjugated SARS strand (at the 3'-end) took place. Interaction with alkaline phosphatase-labelled streptavidin permits amplified indirect electrochemical detection. The analytical signal is constituted by an electrochemical process of indigo carmine, the soluble product of the enzymatic hydrolysis of 3-indoxyl phosphate. The use of a sensitive electrochemical technique such as square wave voltammetry allowed a detection limit of 6 pM to be obtained for this DNA sequence, lower than any other found in the bibliography. The parameters affecting the methodology were studied, with special attention being placed on selectivity. Specificity was clearly enhanced when interaction time and stringency (in the form of formamide percentage) were increased. With 1h of strand interaction and employing 50% of formamide in the hybridisation buffer, a 3-base mismatch strand was perfectly distinguished from the complementary.

Persistence of lung inflammation and lung cytokines with high-resolution CT abnormalities during recovery from SARS

Background

During the acute phase of severe acute respiratory syndrome (SARS), mononuclear cells infiltration, alveolar cell desquamation and hyaline membrane formation have been described, together with dysregulation of plasma cytokine levels. Persistent high-resolution computed tomography (HRCT) abnormalities occur in SARS patients up to 40 days after recovery.

Methods

To determine further the time course of recovery of lung inflammation, we investigated the HRCT and inflammatory profiles, and coronavirus persistence in bronchoalveolar lavage fluid (BALF) of 12 patients at recovery at 60 and 90 days.

Results

At 60 days, compared to normal controls, SARS patients had increased cellularity of BALF with increased alveolar macrophages (AM) and CD8 cells. HRCT scores were increased and correlated with T-cell numbers and their subpopulations, and inversely with CD4/CD8 ratio. TNF-α, IL-6, IL-8, RANTES and MCP-1 levels were increased. Viral particles in AM were detected by electron microscopy in 7 of 12 SARS patients with high HRCT score. On day 90, HRCT scores improved significantly in 10 of 12 patients, with normalization of BALF cell counts in 6 of 12 patients with repeat bronchoscopy. Pulse steroid therapy and prolonged fever were two independent factors associated with delayed resolution of pneumonitis, in this non-randomized, retrospective analysis.

Conclusion

Resolution of pneumonitis is delayed in some patients during SARS recovery and may be associated with delayed clearance of coronavirus, Complete resolution may occur by 90 days or later.

Clinical evaluation of real-time PCR assays for rapid diagnosis of SARS coronavirus during outbreak and post-epidemic periods

BACKGROUND

The protocols of WHO network laboratories facilitated development of rapid diagnosis for SARS coronavirus (CoV) using reverse transcription (RT)-PCR assays. However, several reports have shown that conventional and real-time PCR assays were very specific for SARS CoV but lack sensitivity depending on the assay, specimen, and time course of disease.

OBJECTIVE

To evaluate an automatic nucleic acid extraction system and two standardized real-time PCR assays for rapid diagnosis of SARS CoV during outbreak and post-epidemic periods in Hong Kong.

STUDY DESIGN

Specimens from clinically suspected SARS patients collected during outbreak and post-epidemic periods were tested by an automatic nucleic acid extraction system followed by our first generation conventional RT-PCR and two standardized real-time PCR assays (Artus GmbH, Germany and Roche Diagnostics, Germany). Paired serum samples were assayed for increasing titer against SARS CoV.

RESULTS

In the SARS epidemic, Artus and Roche PCR assays exhibited sensitivities of 87% and 85% for respiratory specimens (n = 64), 91% and 88% for stool (n = 44), and 82% for urine (n = 29). A specificity of 100% was exhibited by both PCR assays except Artus attained only a 92% specificity for stool. For post-epidemic period, no SARS CoV was identified among 56 respiratory specimens by all PCR assays. Inhibitors to PCR assays were detected at an average rate of 7-8% among 202 clinical specimens.

CONCLUSION

This study highlights the high throughput and performance of automatic RNA extraction in coordination with standardized real-time PCR assays suitable for large-scale routine diagnosis in case of future SARS epidemic. As no SARS CoV was detected among specimens collected during post-epidemic period, the positive predictive value of real-time PCR assays for detection of SARS CoV during low epidemic requires further evaluation.

SARS-associated coronavirus transmitted from human to pig

coronavirus (SARS-CoV) was isolated from a pig during a survey for possible routes of viral transmission after a SARS epidemic. Sequence and epidemiology analyses suggested that the pig was infected by a SARS-CoV of human origin.

Epitope mapping and biological function analysis of antibodies produced by immunization of mice with an inactivated Chinese isolate of severe acute respiratory syndrome-associated coronavirus (SARS-CoV)

Inactivated severe acute respiratory syndrome-associated coronavirus (SARS-CoV) has been tested as a candidate vaccine against the re-emergence of SARS. In order to understand the efficacy and safety of this approach, it is important to know the antibody specificities generated with inactivated SARS-CoV. In the current study, a panel of twelve monoclonal antibodies (mAbs) was established by immunizing Balb/c mice with the inactivated BJ01 strain of SARS-CoV isolated from the lung tissue of a SARS-infected Chinese patient. These mAbs could recognize SARS-CoV-infected cells by immunofluorescence analysis (IFA). Seven of them were mapped to the specific segments of recombinant spike (S) protein: six on S1 subunit (aa 12-798) and one on S2 subunit (aa 797-1192). High neutralizing titers against SARS-CoV were detected with two mAbs (1A5 and 2C5) targeting at a subdomain of S protein (aa 310-535), consistent with the previous report that this segment of S protein contains the major neutralizing domain. Some of these S-specific mAbs were able to recognize cleaved products of S protein in SARS-CoV-infected Vero E6 cells. None of the remaining five mAbs could recognize either of the recombinant S, N, M, or E antigens by ELISA. This study demonstrated that the inactivated SARS-CoV was able to preserve the immunogenicity of S protein including its major neutralizing domain. The relative ease with which these mAbs were generated against SARS-CoV virions further supports that subunit vaccination with S constructs may also be able to protect animals and perhaps humans. It is somewhat unexpected that no N-specific mAbs were identified albeit anti-N IgG was easily identified in SARS-CoV-infected patients. The availability of this panel of mAbs also provided potentially useful agents with applications in therapy, diagnosis, and basic research of SARS-CoV.

Characterization of monoclonal antibody against SARS coronavirus nucleocapsid antigen and development of an antigen capture ELISA

This report describes the production of several MAbs against N195 protein, a major immunodomain of SARS CoV nucleocapsid protein [He, Q., Chong, K.H., Chang, H.H., Leung, B., Ling, A.E., Wei, T., Chan, S.W., Ooi, E.E., Kwang, J., 2004. Development of a Western blot assay for detection of antibodies against coronavirus causing severe acute respiratory syndrome. Clin. Diagn. Lab. Immunol. 11 (2) 417–422.]. One representative IgG1 monoclonal antibody (MAb), S-A5D5, was selected and characterized. S-A5D5 reacted specifically react with both recombinant and native nucleocapsid protein of SARS CoV. The reactivity of S-A5D5 with purified N195 protein and utilization of the MAb as a detector antibody to develop an antigen capture ELISA was assessed. As little as 37.5 pg of purified N protein and 50 TCID₅₀ of SARS CoV could be detected by the antigen capture ELISA. Specific binding of the MAb S-A5D5 to both purified N195 and SARS CoV nucleocapsid antigen was effectively inhibited by human SARS positive serum and guinea pig anti-N195 serum. The N protein in N195-spike recombinant baculovirus-infected Sf-9 cells could also be identified. N protein was detected in 18 IFA IgM-positive serum samples collected from SARS confirmed patients, but not in nine samples collected from SARS recovery patient. No false positive results were given when 60 samples from healthy individuals were tested, and no cross-reaction occurred when infectious bronchitis virus (IBV), chicken coronavirus, was tested. This monoclonal antibody-based antigen capture ELISA is thus a powerful tool for early diagnosis of SARS CoV infection.

Duration of RT-PCR positivity in severe acute respiratory syndrome

Severe acute respiratory syndrome (SARS) is a highly infectious respiratory infection with a high mortality. The duration of infectivity is unknown. The RT-PCR positivity for SARS-associated coronavirus (SARS-CoV) was followed in 45 virologically confirmed SARS patients. Serial RT-PCRs for SARS-CoV were performed in the nasopharyngeal aspirate, stool and urine of 45 SARS patients who survived until discharge. All patients had at least one site that was positive for SARS-CoV on presentation. Time to RT-PCR conversion was studied in all patients. There were 15 males (33.3%) and 30 females (66.7%), with a mean+/- SD age of 40.7+/-14.7 yrs. The median (range) time of RT-PCR conversion was 30 days (2-81). On discharge from the hospital, 18 (40%) remained RT-PCR positive in at least one site. For patients with positive RT-PCR on discharge, the median (range) time to RT-PCR conversion after discharge was 13 days (2-60). A significant proportion of severe acute respiratory syndrome patients remained RT-PCR positive for severe acute respiratory syndrome-associated coronavirus for a substantial duration after discharge. The clinical significance is unknown and this finding merits further study. It is prudent to advise patients to adhere to strict personal hygiene on discharge until RT-PCR becomes negative.

Species-independent detection of RNA virus by representational difference analysis using non-ribosomal hexanucleotides for reverse transcription

A method for the isolation of genomic fragments of RNA virus based on cDNA representational difference analysis (cDNA RDA) was developed. cDNA RDA has been applied for the subtraction of poly(A)⁺ RNAs but not for poly(A)⁻ RNAs, such as RNA virus genomes, owing to the vast quantity of ribosomal RNAs. We constructed primers for inefficient reverse transcription of ribosomal sequences based on the distribution analysis of hexanucleotide patterns in ribosomal RNA. The analysis revealed that distributions of hexanucleotide patterns in ribosomal RNA and virus genome were different. We constructed 96 hexanucleotides (non-ribosomal hexanucleotides) and used them as mixed primers for reverse transcription of cDNA RDA. A synchronous analysis of hexanucleotide patterns in known viral sequences showed that all the known genomic-size viral sequences include non-ribosomal hexanucleotides. In a model experiment, when non-ribosomal hexanucleotides were used as primers, in vitro transcribed plasmid RNA was efficiently reverse transcribed when compared with ribosomal RNA of rat cells. Using non-ribosomal primers, the cDNA fragments of severe acute respiratory syndrome coronavirus and bovine parainfluenza virus 3 were efficiently amplified by subtracting the cDNA amplicons derived from uninfected cells from those that were derived from virus-infected cells. The results suggest that cDNA RDA with non-ribosomal primers can be used for species-independent detection of viruses, including new viruses.

Antiviral activity of glycyrrhizic acid derivatives against SARS-coronavirus

Glycyrrhizin (GL) was shown to inhibit SARS-coronavirus (SARS-CoV) replication in vitro. Here the anti-SARS-CoV activity of 15 GL derivatives was tested. The introduction of 2-acetamido-beta-d-glucopyranosylamine into the glycoside chain of GL resulted in 10-fold increased anti-SARS-CoV activity compared to GL. Amides of GL and conjugates of GL with two amino acid residues and a free 30-COOH function presented up to 70-fold increased activity against SARS-CoV but also increased cytotoxicity resulting in decreased selectivity index.

Immunological detection of severe acute respiratory syndrome coronavirus by monoclonal antibodies

In order to establish immunological detection methods for severe acute respiratory syndrome coronavirus (SARS-CoV), we established monoclonal antibodies directed against structural components of the virus. B cell hybridomas were generated from mice that were hyper-immunized with inactivated SARS-CoV virion. By screening 2,880 generated hybridomas, we established three hybridoma clones that secreted antibodies specific for nucleocapsid protein (N) and 27 clones that secreted antibodies specific for spike protein (S). Among these, four S-protein specific antibodies had in vitro neutralization activity against SARS-CoV infection. These monoclonal antibodies enabled the immunological detection of SARS-CoV by immunofluorescence staining, Western blot or immunohistology. Furthermore, a combination of monoclonal antibodies with different specificities allowed the establishment of a highly sensitive antigen-capture sandwich ELISA system. These monoclonal antibodies would be a useful tool for rapid and specific diagnosis of SARS and also for possible antibody-based treatment of the disease.

[Detection of SARS-associated coronavirus N protein by time-resolved fluoroimmunoassay]

OBJECTIVE

To develop a method for quantitative detection of severe acute respiratory syndrome (SARS)-associated coronavirus (SARS-CoV) N protein by timed-resolved fluoroimmunoassay (TRFIA).

METHODS

Using a monoclonal antibody (mAb) against SARS-CoV N protein, screened by SARS-CoV N protein and matching experiment, a method for quantitative detection of SARS-CoV N protein by TRFIA was established on the basis of double sandwich enzyme-linked immunosorbent assay (ELISA) and evaluated against the ELISA kit.

RESULT

The measurement range of the assay was 0.02-150 ng/ml with a sensitivity of 0.02 ng/ml, the coefficient of variability within runs of 3.3%;-6.2%;, and coefficient of variability between days of 5.3%;-9.6%;. The results of detection were consistent between ELISA and TRFIA.

CONCLUSION

TRFIA is a new, sensitive and specific immunoassay for detecting SARS N protein with potential value in clinical applications.

[Development and application of triple antibodies-based sandwich ELISA for detecting nucleocapsid protein of SARS-associated coronavirus]

OBJECTIVE

To prepare and characterize monoclonal antibodies (mAb) and polyclonal antibodies against nucleocapsid (N) protein of severe acute respiratory syndrome (SARS)-associated coronavirus (SARS-CoV) and to establish antibodies-based sandwich ELISA for detecting N protein of SARS-CoV, which might apply to early diagnosis of patients with SARS-CoV infection.

METHODS

BALB/c mice were immunized with purified recombinant N protein of SARS-CoV for producing mAbs, and New Zealand white rabbits were immunized for producing polyclonal antibodies. The identification of antibodies was performed using indirect enzyme-linked immunosorbent assay (ELISA), indirect fluorescent-antibody assay (IFA), and Western immunoblotting. Capturing and detecting antibodies were selected by pairing the mAbs and polyclonal antibodies one by one and an antibodies-based sandwich antigen capture ELISA was used for detecting N antigen of SARS-CoV.

RESULTS

Nine mAbs and hyperimmune rabbit polyclonal antibodies, specifically against SARS-CoV nucleocapsid protein were obtained. Using paired ELISA assay, three mAbs N1E8, N8E1 and N10E4 were selected as capturing antibody and rabbit polyclonal antibodies as detecting antibody then triple antibodies-based sandwich ELISA was established following horseradish peroxidase (HRP)-conjugated goat anti-rabbit immunoglobulin G. The recombinant N protein was used as a standard to establish a detection sensitivity of approximated 50 pg/ml with this assay. When tested with 420 serum specimens from serologically confirmed SARS patients, the positive rates of serum N protein were 90.1%, 23% and 0%, in which sera collected from 1 to 10 days, 11 to 20 days and beyond 21 days respectively after the onset of symptoms. The specificity of the assay was 99.86% in 715 control serum specimens. There was no cross-reaction with other respiratory viruses and coronaviruses.

CONCLUSION

Specific and high affinity mAbs and rabbit polyclonal antibodies were obtained. By paired and optimized sandwich ELISA, a sensitive and specific antigen capture ELISA was established for detecting N antigen of SARS-CoV, which might apply to early diagnosis, source tracing and epidemiological studies of SARS.

Development of a quantitative assay for SARS coronavirus and correlation of GAPDH mRNA with SARS coronavirus in clinical specimens

AIMS

To develop a quantitative reverse transcriptase polymerase chain reaction (Q-RT-PCR) for severe acute respiratory syndrome coronavirus (SARS-CoV) detection and explore the potential of using glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA as an internal control to exclude false negative results.

METHODS

SARS-CoV and GAPDH mRNA were both measured in 26 specimens from 16 patients with SARS, 40 follow up specimens from the same batch of patients, and appropriate control subjects. The relation between SARS positivity and GAPDH mRNA concentration was investigated using the chi2 test. Increasing the sensitivity for SARS-CoV and GAPDH mRNA detection was investigated in follow up specimens in which SARS-CoV and GAPDH mRNA were not detected initially.

RESULTS

Varying amounts of SARS-CoV were found in the 26 SARS-CoV positive specimens and SARS-CoV was not detected in the 40 follow up specimens and controls. In addition, concentrations of GAPDH mRNA were significantly different between the patients with SARS, follow up specimens, and healthy controls (Kruskal-Wallis test, p<0.05). Moreover, GAPDH mRNA concentrations were highly correlated with SARS-CoV positivity (chi2 = 5.43; p<0.05). Finally, SARS-CoV and GAPDH mRNA were both detected in three follow up urine specimens that were initially negative when the amount of cDNA used was increased from 5 microl to 10 and 15 microl.

CONCLUSIONS

This Q-RT-PCR assay can be used to detect SARS-CoV. Moreover, GAPDH mRNA may be useful to rule out false negative results in SARS-CoV detection, and the current extraction method for urine may not be sensitive enough to detect low titres of SARS-CoV.

Comprehensive detection and identification of human coronaviruses, including the SARS-associated coronavirus, with a single RT-PCR assay

The SARS-associated human coronavirus (SARS-HCoV) is a newly described, emerging virus conclusively established as the etiologic agent of the severe acute respiratory syndrome (SARS). This study presents a single-tube RT-PCR assay that can detect with high analytical sensitivity the SARS-HCoV, as well as several other coronaviruses including other known human respiratory coronaviruses (HCoV-OC43 and HCoV-229E). Species identification is provided by sequencing the amplicon, although a rapid screening test by restriction enzyme analysis has proved to be very useful for the analysis of samples obtained during the SARS outbreak in Toronto, Canada.

Detection of airborne severe acute respiratory syndrome (SARS) coronavirus and environmental contamination in SARS outbreak units

Severe acute respiratory syndrome (SARS) is characterized by a risk of nosocomial transmission; however, the risk of airborne transmission of SARS is unknown. During the Toronto outbreaks of SARS, we investigated environmental contamination in SARS units, by employing novel air sampling and conventional surface swabbing. Two polymerase chain reaction (PCR)–positive air samples were obtained from a room occupied by a patient with SARS, indicating the presence of the virus in the air of the room. In addition, several PCR-positive swab samples were recovered from frequently touched surfaces in rooms occupied by patients with SARS (a bed table and a television remote control) and in a nurses’ station used by staff (a medication refrigerator door). These data provide the first experimental confirmation of viral aerosol generation by a patient with SARS, indicating the possibility of airborne droplet transmission, which emphasizes the need for adequate respiratory protection, as well as for strict surface hygiene practices

[An immunofluorescence assay for the detection of SARS associated coronavirus antibody based on recombinant nucleocapsid antigen and its application]

OBJECTIVE

To establish a new technique for SARS-CoV antibody test to detect infection of severer acute respiratory syndrome (SARS).

METHODS

Nucleocapsid gene was obtained by reverse transcription and polymerase chain reaction from a SARS patient and inserted into the vector pFastBacHTa expressing baculovirus. Insect Sf9 cells were transfected with the recombinant baculovirus expressing SARS nucleocapsid antigen and then cultured, fixed by acetone so as to make SARS-specific antigen. Immunofluorescence assay (IFA) technique and plaque reduction neutralization test (PRNT) were used to detect 7 samples of sera of 4 newly diagnosed SARS patients collected in different days, 48 samples of convalescent sera of SARS patients, 24 serum samples of healthy person undergoing physical examination, and 40 serum samples from non-SARS patients with fever by double blind test.

RESULTS

The recombinant SARS-specific antigen reacted only with SARS positive sera but not with normal sera. Double blind test showed that 45 of the 46 PRNT positive sera were IFA positive with an accordance rate of 97.8%. 7 samples of sera from 4 SARS patients in acute progressive stage in Guangdong province were all IFA positive. SARS antibody could be detected since the sixth day after onset, and the titer increased from 1:40 to 1:600 on the ninth day.

CONCLUSION

Immunofluorescence assay is highly specific and sensitive in detection of SARS. This reagent is safe and easy to prepare.

Determination of SARS-coronavirus by a microfluidic chip system

We have developed a new experimental system based on a microfluidic chip to determine severe acute respiratory syndrome coronavirus (SARS‐CoV). The system includes a laser‐induced fluorescence microfluidic chip analyzer, a glass microchip for both polymerase chain reaction (PCR) and capillary electrophoresis, a chip thermal cycler based on dual Peltier thermoelectric elements, a reverse transcription‐polymerase chain reaction (RT‐PCR) SARS diagnostic kit, and a DNA electrophoretic sizing kit. The system allows efficient cDNA amplification of SARS‐CoV followed by electrophoretic sizing and detection on the same chip. To enhance the reliability of RT‐PCR on SARS‐CoV detection, duplex PCR was developed on the microchip. The assay was carried out on a home‐made microfluidic chip system. The positive and the negative control were cDNA fragments of SARS‐CoV and parainfluenza virus, respectively. The test results showed that 17 positive samples were obtained among 18 samples of nasopharyngeal swabs from clinically diagnosed SARS patients. However, 12 positive results from the same 18 samples were obtained by the conventional RT‐PCR with agarose gel electrophoresis detection. The SARS virus species can be analyzed with high positive rate and rapidity on the microfluidic chip system.

[Molecular cloning and expression of the severe acute respiratory syndrome-associated coronavirus nucleocapsid protein and its clinical application]

OBJECTIVE

To clone and express nucleocapsid (N) protein of the severe acute respiratory syndrome (SARS)-associated coronavirus, and to evaluate its antigenicity and application value in the development of serological diagnostic test for SARS.

METHODS

SARS-associated coronavirus N protein gene was amplified from its genomic RNA by reverse transcript nested polymerase chain reaction (RT-nested-PCR) and cloned into pBAD/Thio-TOPO prokaryotic expression vector. The recombinant N fusion protein was expressed and purified, and its antigenicity and specificity was analyzed by Western Blot, to establish the recombinant N protein-based ELISA for detection of IgG antibodies to SARS-associated coronavirus, and SARS-associated coronavirus lysates-based ELISA was compared parallelly.

RESULTS

The recombinant expression vector produced high level of the N fusion protein after induction, and that protein was purified successfully by affinity chromatography and displayed higher antigenicity and specificity as compared with whole virus lysates.

CONCLUSION

The recombinant SARS-associated coronavirus N protein possessed better antigenicity and specificity and could be employed to establish a new, sensitive, and specific ELISA for SARS diagnosis.

[Study on the RNA of severe acute respiratory syndrome (SARS) associated coronavirus in the blood and excretion of convalescent patients with SARS]

OBJECTIVE

To examine the RNA of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) in the blood and excretion of convalescent patient with SARS for prevention and treatment of the disease.

METHODS

A total of 276 samples, including plasma, urine, feces and sputum, obtained from 23 convalescent patients with SARS were studied at 3 time-points at least 21 days after the onset of symptoms. RNA was extracted and nested reverse transcription-polymerase chain reaction (RT-PCR) was carried out using SARS-CoV specific primers.

RESULTS

Among the 276 samples, SARS-CoV RNA was detected in 6 cases (38.8%) by nested RT-PCR. The positive rates of SARS-CoV RNA was 5.8% in feces and 2.9% in sputum samples but SARS-CoV RNA was not detectable in plasma and urine of all the cases.

CONCLUSION

The existence of SARS-CoV RNA in the excretion of some convalescent patients with SARS showed that the excretion from these patients should be carefully treated whilthe re-transmission of SARS by which, should be further studied.

Immunohistochemical, in situ hybridization, and ultrastructural localization of SARS-associated coronavirus in lung of a fatal case of severe acute respiratory syndrome in Taiwan

This article describes the pathological studies of fatal severe acute respiratory syndrome (SARS) in a 73-year-old man during an outbreak of SARS in Taiwan, 2003. Eight days before onset of symptoms, he visited a municipal hospital that was later identified as the epicenter of a large outbreak of SARS. On admission to National Taiwan University Hospital in Taipei, the patient experienced chest tightness, progressive dyspnea, and low-grade fever. His condition rapidly deteriorated with increasing respiratory difficulty, and he died 7 days after admission. The most prominent histopathologic finding was diffuse alveolar damage of the lung. Immunohistochemical and in situ hybridization assays demonstrated evidence of SARS-associated coronavirus (SARS-CoV) infection in various respiratory epithelial cells, predominantly type II pneumocytes, and in alveolar macrophages in the lung. Electron microscopic examination also revealed coronavirus particles in the pneumocytes, and their identity was confirmed as SARS-CoV by immunogold labeling electron microscopy. This report is the first to describe the cellular localization of SARS-CoV in human lung tissue by using a combination of immunohistochemistry, double-stain immunohistochemistry, in situ hybridization, electron microscopy, and immunogold labeling electron microscopy. These techniques represent valuable laboratory diagnostic modalities and provide insights into the pathogenesis of this emerging infection.

Molecular genetic methods in the diagnosis of lower respiratory tract infections

Molecular diagnostic techniques, such as PCR, have become useful tools for the rapid etiological diagnosis of lower respiratory tract infections. Nucleic acid amplification tests (NAATs) have been evaluated for detecting most respiratory pathogens, and commercial assays are available for some pathogens. However, standardized protocols are needed before these assays are introduced into routine diagnostic use. For pneumonia, NAATs offer advantages over conventional tests for the detection of Mycoplasma pneumoniae, Legionella spp. and Chlamydia pneumoniae. For pneumococcal pneumonia in adults, PCR adds little to existing diagnostic tests, and is unable to distinguish pneumococcal colonization from infection when testing respiratory samples. Although less sensitive than culture-based methods, several commercial molecular diagnostic assays have been developed for tuberculosis and are useful rapid tests for selected patients. PCR can now be considered the rapid diagnostic test of choice for pertussis and some respiratory virus infections. Further work is required to better characterize the role of molecular diagnostic tests for diagnosing lower respiratory tract infections, and to develop standard assays that can be readily adopted by routine diagnostic laboratories.

SARS molecular detection external quality assurance

Inactivated severe acute respiratory syndrome–associated coronavirus samples were used for an external quality assurance study within the World Health Organization SARS Reference and Verification Network and other reference institutions. Of 58 participants, 51 correctly detected virus in all samples >9,400 RNA copies per milliliter and none in negative samples. Commercial test kits significantly improved the outcome.

Antibodies to SARS coronavirus in civets

Using three different assays, we examined 103 serum samples collected from different civet farms and a market in China in June 2003 and January 2004. While civets on farms were largely free from SARS-CoV infection, ≈80% of the animals from one animal market in Guangzhou contained significant levels of antibody to SARS-CoV, which suggests no widespread infection among civets resident on farms, and the infection of civets in the market might be associated with trading activities under the conditions of overcrowding and mixing of various animal species.

Reference gene selection for quantitative real-time PCR analysis in virus infected cells: SARS corona virus, Yellow fever virus, Human Herpesvirus-6, Camelpox virus and Cytomegalovirus infections

Ten potential reference genes were compared for their use in experiments investigating cellular mRNA expression of virus infected cells. Human cell lines were infected with Cytomegalovirus, Human Herpesvirus-6, Camelpox virus, SARS coronavirus or Yellow fever virus. The expression levels of these genes and the viral replication were determined by real-time PCR. Genes were ranked by the BestKeeper tool, the GeNorm tool and by criteria we reported previously. Ranking lists of the genes tested were tool dependent. However, over all, β-actin is an unsuitable as reference gene, whereas TATA-Box binding protein and peptidyl-prolyl-isomerase A are stable reference genes for expression studies in virus infected cells.

A universal microarray for detection of SARS coronavirus

Severe acute respiratory syndrome (SARS) is caused by the SARS coronavirus (SARS-CoV). There are many point mutations among SARS-CoV genome sequences. Previous studies suggested that the mutations are correlated closely with the SARS epidemic. It was found that the bases of six nucleotide positions (nt9404, nt9479, nt19838, nt21721, nt22222 and nt27827) with high-mutation rate have an important relationship with the SARS epidemic. For viral detection as well as genotyping, a universal microarray system was developed that combines RT-PCR and ligase detection reaction (LDR). The Zip Codes attached covalently to a slide remain constant and their complementary Zip Codes (cZip Codes) can be used for tagging target sequence, making the microarrays universal. The discriminating oligonucleotides contain on the 5′ end “cZip Codes” that are used to direct LDR product to specific Zip Codes attached covalently to a slide. Since Zip Codes have no homology to either the target sequence or to other sequences in the genomes of both human host and SARS-CoV, there was no false signal due to mismatch hybridizations. 20 samples assayed with the universal microarray were confirmed by DNA sequencing, demonstrating that this microarray system is a promising diagnostic tool for detection and genotyping of the SARS-CoV.

Development and evaluation of an efficient 3'-noncoding region based SARS coronavirus (SARS-CoV) RT-PCR assay for detection of SARS-CoV infections

The severe acute respiratory syndrome (SARS) epidemic originating from China in 2002 was caused by a previously uncharacterized coronavirus that could be identified by specific RT-PCR amplification. Efforts to control future SARS outbreaks depend on the accurate and early identification of SARS-CoV infected patients. A real-time fluorogenic RT-PCR assay based on the 3′-noncoding region (3′-NCR) of SARS-CoV genome was developed as a quantitative SARS diagnostic tool. The ideal amplification efficiency of a sensitive SARS-CoV RT-PCR assay should yield an E value (PCR product concentration increase per amplification cycle) equal to 2.0. It was demonstrated that the 3′-NCR SARS-CoV based RT-PCR reactions could be formulated to reach excellent E values of 1.81, or 91% amplification efficacy. The SARS-CoV cDNA preparations derived from viral RNA extract and the cloned recombinant plasmid both exhibit the identical amplification characteristics, i.e. amplification efficacy using the same PCR formulation developed in this study. The viral genomic copy (or genomic equivalences, GE) per infectious unit (GE/pfu) of SARS-CoV used in this study was also established to be approximate 1200–1600:1. The assay’s detection sensitivity could reach 0.005 pfu or 6–8 GE per assay. It was preliminarily demonstrated that the assay could efficiently detect SARS-CoV from clinical specimens of SARS probable and suspected patients identified in Taiwan. The 3′-NCR based SARS-CoV assay demonstrated 100% diagnostic specificity testing samples of patients with acute respiratory disease from a non-SARS epidemic region.

Cross-host evolution of severe acute respiratory syndrome coronavirus in palm civet and human

The genomic sequences of severe acute respiratory syndrome coronaviruses from human and palm civet of the 2003/2004 outbreak in the city of Guangzhou, China, were nearly identical. Phylogenetic analysis suggested an independent viral invasion from animal to human in this new episode. Combining all existing data but excluding singletons, we identified 202 single-nucleotide variations. Among them, 17 are polymorphic in palm civets only. The ratio of nonsynonymous/synonymous nucleotide substitution in palm civets collected 1 yr apart from different geographic locations is very high, suggesting a rapid evolving process of viral proteins in civet as well, much like their adaptation in the human host in the early 2002-2003 epidemic. Major genetic variations in some critical genes, particularly the Spike gene, seemed essential for the transition from animal-to-human transmission to human-to-human transmission, which eventually caused the first severe acute respiratory syndrome outbreak of 2002/2003.

Clinical characteristics and mechanism of liver damage in patients with severe acute respiratory syndrome

BACKGROUND

Abnormal liver function was found in patients with severe acute respiratory syndrome (SARS). This study was undertaken to explore the clinical characteristics and mechanisms of liver damage.

METHODS

The serial laboratory data of liver function test and hepatic histological examination from 168 patients with SARS were retrospectively analyzed.

RESULTS

The abnormalities of serum alanine aminotransferase (ALT) were 52.5%, 71.8%, 85.7% and 85.2%. The average levels of ALT of the patients were 56.07+/-51.57 U/L, 86.46+/-69.93 U/L, 106.69+/-102.50 U/L and 111.32+/-160.24 U/L, and the average levels of serum albumin were 37.25+/-5.37 g/L, 35.82+/-4.74 g/L, 34.49+/-5.04 g/L, and 34.26+/-4.70 g/L, at the day of admission, the first week, second week, and third week after hospitalization, respectively. Significant correlation was not shown among liver damage, blood oxygen saturation (SaO2), degree of fever, and immune functional disorder in this study. Hepatic histological examination of 4 patients demonstrated that non-specific inflammation existed in the liver.

CONCLUSIONS

Liver damage of patients with SARS usually occurs in the early stage of the disease with a high occurrence rate and a prolonged profile, which can be characterized by early, obvious decrease of albumin levels and slightly abnormal levels of ALT. The liver damage induced by SARS seems to be caused by SARS virus directly rather than by low SaO2 or high fever. Hepatotoxic drugs may play a role in increasing the severity of liver damage or prolonging the time of liver function recovery.

[Surveillance on severe acute respiratory syndrome associated coronavirus in animals at a live animal market of Guangzhou in 2004]

OBJECTIVE

To study the prevalence of severe acute respiratory syndrome coronavirus (SARS-CoV) like virus in animals at a live animal market of Guanzhou in 2004 before and after culling of wild animal action taken by the local authority, in order to predict the re-emerging of SARS from animal originals in this region.

METHODS

Animals at live animal market were sampled for rectal and throat swabs in triplicate. A single step realtime reverse transcription-polymerase chain reaction (RT-PCR) diagnostic kit was performed for screening SARS-CoV like virus, the manual nested RT- PCR and DNA sequencing were performed for confirmation. Only specimens which tested positive for both of the N and P genes by nested RT-PCR were scored as positive.

RESULTS

In 31 animals sampled in January 5 2004 before culling of wild animals at Guangdong Province, including 20 cats (Felis catus), 5 red fox (Vulpes vulpes) and 6 Lesser rice field rats (Rattus losea), 8 (25.8%) animals were tested positive for SARS-CoV like virus by RT-PCR methods, of which 4 cats, 3 red fox and one Lesser rice field rats were included. However, two weeks after culling of animals and disinfection of the market were implemented, in 119 animals sampled in January 20 2004, including 6 rabbits (Oryctolagus cuniculus), 13 cats, 46 red jungle fowl (Gallus gallus), 13 spotbill duck (Anas platyrhynchos), 10 greylag goose (Anser anser), 31 Chinese francolin (Franclinus pintadeanus), only rectal swab from one greylag goose was tested positive for SARS-CoV like virus. Furthermore, in 102 animals that including 14 greylag gooses, 3 cats, 5 rabbits, 9 spotbill duck (Anaspoecilorhyncha), 2 Chinese francolin (Franclinus pintadeanus), 8 common pheasant (Phasianus colchicus), 6 pigeons, 9 Chinese muntjac (Muntiacus reevesi), 19 wild boar (Sus scrofa), 16 Lesser rice field rats, 5 dogs, 1 mink (Mustela vison), 3 goats, 2 green peafowl (Pavo muticus) sampled in April, May, June, July, August and November, only rectal swab from one pig was tested positive. However, of 12 and 10 palm civets sampled in November and December including five of which had been at the live animals market for 2 days, none of them was tested positive.

CONCLUSION

This findings revealed that animals being sampled in April, May, June, July, August and November of 2004, only one rectal swab from a pig was tested positive as SARS-CoV like virus, much lower than the results from the previous year, suggesting that the possibility of re-emerging of human infection from animal origins is low for the winter of 2004-2005.

Novel immunofluorescence assay using recombinant nucleocapsid-spike fusion protein as antigen to detect antibodies against severe acute respiratory syndrome coronavirus

Severe acute respiratory syndrome (SARS) is caused by a novel and highly infectious virus named SARS coronavirus (SARS-CoV). Among the serological tests currently available for the detection of SARS-CoV, a whole-virus-based immunofluorescence assay (IFA) was considered one of the most sensitive assays and served as a "gold standard" during the SARS epidemic in Singapore in 2003. However, the need to manipulate live SARS-CoV in the traditional IFA limits its wide application due to the requirement for a biosafety level 3 laboratory and the risk of laboratory infection. Previously, we have identified two immunodominant epitopes, named N195 and Sc, in the two major structural proteins, the N and S proteins, of SARS-CoV (Q. He, K. H. Chong, H. H. Chng, B. Leung, A. E. Ling, T. Wei, S. W. Chan, E. E. Ooi, and J. Kwang, Clin. Diagn. Lab. Immunol., 11:417-422, 2004; L. Lu, I. Manopo, B. P. Leung, H. H. Chng, A. E. Ling, L. L. Chee, E. E. Ooi, S. W. Chan, and J. Kwang, J. Clin. Microbiol. 42:1570-1576, 2004). In the present study, the N195-Sc fusion protein was highly expressed in insect (Sf9) cells infected with a recombinant baculovirus bearing the hybrid gene under the control of a polyhedrin promoter. An IFA based on Sf9 cells producing the fusion protein was standardized with 23 serum samples from patients with SARS, 20 serum samples from patients with autoimmune diseases, and 43 serum samples from healthy blood donors. The detection rates were comparable to those obtained with a commercial SARS-CoV IFA kit (EUROIMMUN, Gross Groenau, Germany) and a conventional IFA performed at the Singapore General Hospital. Our data showed that the newly developed IFA could detect SARS-CoV in 22 of the 23 SARS-CoV-positive serum samples and gave no false-positive results when the sera from patients with autoimmune diseases and healthy individuals were tested. The detection rate was identical to those of the two whole-virus-based IFAs. Thus, the novel N-S fusion antigen-based IFA could be an attractive alternative to present whole-virus-based IFAs for the diagnosis of SARS-CoV infection.

The design and application of DNA chips for early detection of SARS-CoV from clinical samples

Background:

SARS coronavirus has been identified as the cause of severe acute respiratory syndrome (SARS). Few tests allow confirmation or exclusion of SARS within the first few days of infection. A gene chip is a useful tool for the study of microbial infections mainly for its capability of performing multi-target analysis in a single test.

Objectives:

Investigate the possibility of early detection of SARS virus from clinical samples using the gene chip-based method.

Study design:

We purified RNA from SARS-CoV obtained from routinely collected peripheral blood and sputum samples of 34 patients who had been identified as probable SARS patients by following the interim U.S. case definition. Four segments of the SARS-CoV were amplified using reverse transcription-nested PCR and the products examined using the 70-mer gene chips for SARS-CoV detection.

Results:

A blind-test of both peripheral blood and sputum specimens lead to the positive detection of SARS-CoV in 31 out of 34 patients. SARS-CoV was not found in peripheral blood or sputum specimens from three patients. Two of the 34 patients were only 3 days post-onset of symptoms and were subsequently confirmed to be SARS positive. Our results indicate that the gene chip-based molecular test is specific for SARS-CoV and allows early detection of patients with SARS with detection rate about 8% higher than the single PCR test when the sputum sample is available.

Severe acute respiratory syndrome associated coronavirus is detected in intestinal tissues of fatal cases

OBJECTIVES

A significant percentage of confirmed severe acute respiratory syndrome (SARS) patients experienced gastrointestinal symptoms, and the viral sequence was detectable in the stool of most patients. At present, the knowledge of the pathology of the digestive system in SARS patients is limited. Because a resurgence of the SARS epidemic is constantly possible, there is an urgent need to understand the involvement of the digestive system in this new disease.

METHODS

We performed seven SARS autopsies in which samples of alimentary tract and digestive glands were examined with routine pathology, electron microscopy (EM), in situ hybridization (ISH), immunohistochemistry, and real-time polymerase chain reaction (PCR).

RESULTS

The main histopathological finding was atrophy of the mucosal lymphoid tissue. A few mucosal epithelial cells and lymphocytes in the intestine were positively stained for coronavirus with ISH. SARS-coronavirus (CoV)-like particles were found in the mucosal epithelial cells under EM and mild focal inflammation was detected in the alimentary tract. One patient who experienced severe diarrhea had pseudomembranous enteritis of the ileum. Fatty degeneration and central lobular necrosis were observed in the liver. No evidence of direct viral infection was found in the esophagus, the stomach, the salivary gland, the liver, or the pancreas.

CONCLUSIONS

In addition to the lungs, the gastrointestinal tract is another target of SARS-CoV infection, as the intestinal epithelial cells and mucosal lymphoid tissue are infected. The findings provide possible explanations for the gastrointestinal symptoms and the presence of virus in the stool of SARS patients.

[SARS corona virus--a new dilemma]

In late 2002, cases of life-threatening respiratory disease with no identifiable cause were reported from Guangdong Province, China, and they were followed by reports from other countries. The syndrome was designated "severe acute respiratory syndrome" (SARS). Investigators used a combination of traditional methods and molecular techniques to identitify the unknown pathogen. Researches showed that SARS is caused by a new coronavirus, never detected before and which is not related to any of the known coronaviruses.

[Severe acute respiratory syndrome. The public health laboratory in a global emergency]

By the end of year 2002 there was an outbreak of atypical pneumonia in Southeast Asia which soon spread to other continents. This new severe acute respiratory syndrome (SARS) was produced by a novel coronavirus. Due to the severity of the situation and risk of introduction of this pathology in our country, the need to arrange specific laboratory diagnostic tests arose. Classic techniques, such as the electron microscopy and molecular biology test such as retrotranscription followed by the polymerase chain reaction (RT-PCR) were implemented. The araldit included cells infected with bovine coronavirus which allowed the viral particles to be visualized easily but it took more time in comparison with the negative staining of free particles from viral cultures. RT-PCR was able to detect RNA of isolated viruses from cases in Hong Kong and Germany.

[The effects of 4 laboratory test kits in early detecting of severe acute respiratory syndrome coronavirus]

OBJECTIVE

To compare the 4 test kits on severe acute respiratory syndrome coronavirus (SARS-CoV) gene, antigen and antibody for early diagnose of SARS patients.

METHODS

Three enzyme linked immunosorbent assay (ELISA) kits were used to detect SARS-CoV IgG, IgM and N protein and fluorescent polymerase chain reaction (F-PCR) kit was used to detect SARS-CoV RNA.

RESULTS

In 162 serum samples, 90.2% (55/61) became N protein positive in 1 - 5 days and 92.8% (13/14) became positive IgM and IgG in 15 - 18 days after the onset of disease, respectively. On 82 gorgling samples, the positive rates of F-PCR were 56.3% (14/24) in 1 - 5 days and 71.4% (10/14) in 6 - 9 days after the onset.

CONCLUSION

Other than F-PCR, N protein had good effect in the early detection on dubious patients which could lead to effective prevention and control of the epidemic.

Concentration and detection of SARS coronavirus in sewage from Xiao Tang Shan Hospital and the 309th Hospital of the Chinese People's Liberation Army

A worldwide outbreak of severe acute respiratory syndrome (SARS) had been reported. Over 8439 SARS cases and 812 SARS-related deaths were reported to the World Health Organization from 32 countries around the world up to 5 July 2003. The mechanism of transmission of SARS-CoV has been limited only to close contacts with patients. Attention was focused on possible transmission by the sewage system because laboratory studies showed that patients excreted coronavirus RNA in their stools in Amoy Gardens in Hong Kong. To explore whether the stool of SARS patients or the sewage containing the stool of patients would transmit SARS-CoV or not, we used a style of electropositive filter media particle to concentrate the SARS-CoV from the sewage of two hospitals receiving SARS patients in Beijing, as well as cell culture, semi-nested RT-PCR and sequencing of genes to detect and identify the viruses from sewage. There was no live SARS-CoV detected in the sewage in these assays. The nucleic acid of SARS-CoV was found in the sewage before disinfection from both hospitals by PCR. After disinfection, SARS-CoV RNA could be detected from some samples from the 309th Hospital of the Chinese People's Liberation Army, but not from Xiao Tang Shan Hospital after disinfection. In this study, we found that the virus can survive for 14 days in sewage at 4 degrees C, 2 days at 20 degrees C, and its RNA can be detected for 8 days though the virus had been inactivated. In conclusion, this study demonstrates that the RNA of SARS-CoV could be detected from the concentrates of sewage of both hospitals receiving SARS patients before disinfection and occasionally after disinfection though there was no live SARS-CoV; thus much attention should be paid to the treatment of stools of patients and the sewage of hospitals receiving SARS patients.