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Posted: June 28th, 2022
SARS Surveillance, Diagnostic Screening and Testing
SARS Surveillance, Diagnostic Screening and Testing
The United States Center For Disease Control and Prevention(CDC) started an emergency public health response in March 2003 and set up a national surveillance for SARS. Its main focus was on identifying patient cases in the country and determining whether domestic transmission was happening (CDC, 2020). This surveillance system used clinical, epidemiologic and laboratory criteria targeted on early detection in patients with severe unexplained respiratory infections that could be linked to SARS. SARS’ symptoms related to the atypical clinical pneumonia that were not responding to the antimicrobial treatment and could fast progress to severe respiratory distress and death. This led to a problem in public health and healthcare delivery systems globally. National surveillance hence started on March 17, 2003 which was three days after the start of the emergency response by CDC.
Over 1000 unexplained respiratory illnesses were reported between March 17 and July 30, 2003. The reports were made at the state and local health departments then transmitted to the CDC. 27% of the case reports met the clinical and epidemiologic SARS case criteria with 18% of them being probable cases with evidence of pneumonia (CDC, 2020). Eight of the cases or 2% were confirmed SARS infections who had radiographic evidence of pneumonia. Six of the eight were identified in the first surveillance month, 206 or 52% were negative while 184 cases or 46% were under undetermined status due to missing serum specimens. 31% of those who met the SARS case criteria were hospitalized with all of them surviving.
The diagnosis of SARS was primarily based on clinical and epidemiological findings. Molecular tests would be incorporated to diagnose as SARS-CoV-specific RNA could be detected in several clinical specimens including blood, stool, respiratory secretions or body tissues by the polymerase chain reaction (PCR). Additionally, a 5Z-nuclease RT-PCR test kit that had primers and positive and negative controls that were established by the Bernhard Nocht Institute. A valid positive PCR result indicated that there is genetic material (RNA) from the SARS-CoV in the sample. However, it did not mean that the present virus was infectious or it was large enough to infect another individual.
The presence of the infectious virus could be detected through an inoculation of the suitable cell cultures such as vero cells with the patient specimens and having the virus propagated in vitro. After it is isolated, the virus needs to be identified as SARS-CoV through further testing (Christian & Dristen, n.d.). Cell culture was a very demanding test but remained to be the only means to demonstrate the existence of a live virus. It was to be undertaken under at least biosafety safety level (BSAL) three conditions. The positive cell culture results indicated the presence of live SARS-CoV in in the tested sample. The negative cell culture results would not however exclude SARS.
Several strategies provided a means of detecting antibodies produced in responding to infections with SARS-CoV (Christian & Dristen, n.d.). The distinct types of antibodies (IgM and IgG) appeared and changed uin level during the infection’s course. The antibodies could be undetectable in the initial stages of infection. IgG usually remains detectable even after the illness resolution. Therefore, some of the tests developed included enzyme-linked immunosorbent assay (ELISA) which was a test that detected a mixture of IgM and IgG antibodies in the serum of the SARS patients and reliably yielded positive results at around the 21st day after the onset of illness.
The second test format was the immunofluorescence assay (IFA) which required using SARS-CoV-infected cells fixed in the microscope slide and the patient antibodies bind to the viral antigens hence detected by the immunofluorescent-labeled secondary antibodies against human IgG or IgM or the two with the use if the immunofluorescence microscope (Christian & Dristen, n.d.). IFA normally yielded a positive result after the 10th after the onset of the illness. Results were quantified through the use of serial titrations of patient sera. The third test format was the neutralization test which assessed and quantified through titration. It focussed on the ability of the patient sera to neutralize the infectivity of SARS-COV on the cell culture. This test was considered the best correlate of immunity. However, since it used the infectious virus then it was limited to institutions with BSL-3 facilities.
Positive antibody test results indicated a past infection with SARS-CoV. Seroconversion from negative to positive or the four-fold rise in the antibody titer from acute to convalescent serum indicates a recent infection (Christian & Dristen, n.d.). The negative antibody test result after 21 days from the oiliness’ onset indicated the likelihood of no infection with SARS-CoV has happened. There seemed to be no background seroprevalence against SARS-CoV in the control populations. Antibody testing allows the indirect diagnosis of SARS-CoV infection and infection and is not suitable during an acute illness. It had the advantage of being independent of tyej sample type and timing compared to the virus detection methods.
CDC. (2020, September 24). SARS | Guidance | 2003 surveillance plan | Cov disease | CDC. Retrieved from https://www.cdc.gov/sars/guidance/b-surveillance/cases.html
Christian, H. O., & Dristen, C. (n.d.). Diagnostic tests. Retrieved from https://sarsreference.com/sarsref/tests.htm
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