Credit CDC PHIL
# 8676
With lab tests, we’d all like to believe that results are always binary; either positive or negative - with no ambiguity - and certainly no false readings. The two main measures of the accuracy of any diagnostic test are sensitivity and specificity.
- Sensitivity is defined as the ability of a test to correctly identify individuals who have a given disease or condition.
- Specificity is defined as the ability of a test to exclude someone from having a disease or illness.
But the truth is, all lab tests have limitations. And the MERS serological tests currently being used and evaluated by the CDC are no exception.
Just over 10 days ago the big infectious disease story was: CDC: Contact Of Indiana MERS Case Tests Positive For The Virus.
The contact was reportedly well, but based on early testing - had seroconverted – developed antibodies to the virus indicating prior infection. Today, at a 1pm press conference announced late this morning, the CDC has backtracked on those findings, after more complete testing has been completed.
Press Release
Embargoed until 1 p.m. ET
Wednesday, May 28, 2014
Contact: CDC Media Relations
(404) 639-3286
CDC concludes Indiana MERS patient did not spread virus to Illinois business associate
After completing additional and more definitive laboratory tests, CDC officials have concluded that an Indiana MERS patient did not spread the virus to an Illinois associate during a business meeting they had before the patient became ill and was hospitalized.
CDC and state and local public health officials are conducting voluntary testing of people who had contact with two travelers who went from Saudi Arabia to the U.S. where they were confirmed to have Middle East Respiratory Syndrome, or MERS. One type of tests conducted by state and CDC labs uses respiratory samples and can quickly indicate if a person has active infection with the virus. These tests are called PCR, or polymerase chain reaction, assays. Another type of testing, conducted on blood samples in CDC labs, is called serology and is designed to look for antibodies to Middle East Respiratory Syndrome Coronavirus (MERS-CoV). Antibodies would indicate that a person had been previously infected with the virus and developed an immune response. To conduct serology for MERS-CoV, CDC performs three separate tests – ELISA or enzyme-linked immunosorbent assay, IFA or immunofluorescent assay, and a third more definitive test called the neutralizing antibody assay which takes longer than the other two tests.
The Illinois resident, a business associate who had extended face-to-face contact with the Indiana MERS patient, tested negative for active MERS-CoV infection by PCR in the days after his interaction with the man. Given the Illinois man’s contact with the MERS patient, CDC conducted serology testing to see if the Illinois man had antibodies to MERS-CoV. Preliminary ELISA and IFA results announced by CDC on May 17 indicated that the Illinois resident appeared to be positive for MERS-CoV antibodies.
“The initial ELISA and IFA serology results indicated the possibility that the Illinois resident had been previously infected with MERS-CoV,” said David Swerdlow, M.D., who is leading CDC’s MERS-CoV response. “This compelled us to notify and test those people with whom he had close contact in the days following his interaction with the Indiana MERS patient.”
CDC scientists have since tested additional blood samples and completed the slower, definitive serology test, the neutralizing antibody test, which requires at least five days before a result is available. Based on the result of all of these tests, which require careful interpretation, CDC has concluded that the Illinois resident was not previously infected with MERS-CoV.
“While we never want to cause undue concern among those who have had contact with a MERS patient, it is our job to move quickly when there is a potential public health threat,” said Swerdlow. “Because there is still much we don’t know about this virus, we will continue to err on the side of caution when responding to and investigating cases of MERS in this country.”
To date, active MERS-CoV infection has not been found in any of the contacts of the two people in the U.S. confirmed to have the disease. However, investigations are ongoing, including voluntary serology testing of contacts. This vigilant approach is intended to help CDC reduce any immediate public health threat, as well as help the global scientific community gain a better understanding of how MERS-CoV spreads so we can more effectively control this disease in the future. There is currently no evidence of sustained spread of MERS-CoV in community settings.
As CDC continues to gather additional information, officials will update the agency’s MERS recommendations as needed. At this time, CDC’s recommendations to the public, travelers, doctors and other healthcare providers have not changed.
