SARS proteins included in positive proteins samples are: S protein (surface, 180 kD), E protein (envelope, 32 kD), M protein (membrane, 29 kD) and N protein (nucleoprotein, 50 kD). SARS protein sequences are from SARS coronavirus Urbani (accession number AY278741). Negative proteins samples include human proteins commonly found in throat swab samples: Albumin (69 kD), Apolipoprotein A1 (31 kD), Cystatin S (16 kD) and Serotransferrin (77 kD).
For positive cDNA samples, the N gene sequence is added to the normal human sequences described above for the infectious disease cases. Primers are designed to amplify the entire coding sequence. The same sequences are used for all samples, so the DNA samples for PCR are not suitable for certain bioinformatics applications such as tree building.
Note: An ELISA test is considered positive if the color production (absorbance) for a sample is at least twice the negative control value. PCR results are recorded as viral load values, i.e. how many copies of the virus were detected.
Case A. Dr. Smith, a physician at a hospital in Hamilton, Ontario observed four cases of what appeared to be a viral pneumonia within the last week. The symptoms resemble those associated with SARS. The patients all had high fevers and difficulty breathing, and their x-rays showed signs of pneumonia. Bacterial cultures were negative. None of the patients reported traveling out of the country recently. The first patient who was admitted seems to be recovering, but the second patient has taken a turn for the worse, and may not last the night. Dr. Smith remembers very well the SARS outbreak in Toronto, just one hour north of Hamilton. Most of the more than 300 people infected were exposed to the virus while in a Toronto hospital, as a patient or visitor. Some of the casualties were health care workers who contracted the virus while treating patients. He and the rest of the clinical staff have been taking every possible precaution, and the patients are in an isolation ward in the hospital. Dr. Smith is anxiously awaiting the results of the laboratory tests.
- Patient 1 (57-year-old male) – positive for SARS-CoV by ELISA and PCR
- Patient 2 (51-year old female, wife of patient 1) – positive for SARS-CoV by ELISA and PCR
- Patient 3 (43-year-old female) – negative by ELISA, positive for SARS-CoV by PCR
- Patient 4 (69-year old male) – negative by ELISA and PCR
Case B. Shi Jiao-hui has lived in the New York City almost all of this life. His parents moved there when he was two years old. He is a U.S. citizen and considers himself a New Yorker, but the rest of his extended family still lives in Guangdong province in China. Finally, at age 30, he and his wife, Ming, and their son and daughter traveled to China to visit his relatives and see his homeland. Their 3-week trip took them through Hong Kong and several cities in China, and they spent the last week with relatives near the city of Guangzhou. Unfortunately, Ming was very sick most of that week. She had a high fever and difficulty breathing. She was taken to a hospital in Guangzhou where she was treated for pneumonia. She recovered enough to fly back home and is doing fine now. However, Jiao felt ill soon after returning home and now has the same symptoms as Ming. When he goes to the clinic the physician is alarmed by the description of the symptoms and the fact that the family had recently visited the area where SARS was first reported. He recommends that Jiao be tested for SARS coronavirus infection and collects a throat swab. He also recommends that the two children be brought in for testing. In the meantime, Jiao is hospitalized and placed in an isolation ward.
- Jiao – positive for SARS CoV by ELISA and PCR
- Son – negative by ELISA and PCR
- daughter – negative by ELISA and PCR
- Ming – positive for antibodies to SARS CoV