The World Health Organization (WHO) today offered revised recommendations on lab testing for Middle East respiratory syndrome coronavirus (MERS-CoV), including advice about using caution with serologic tests because they have not been extensively validated.
Meanwhile, a machine-translated statement from the Saudi Arabian Ministry of Health (MOH) today reported three more MERS-CoV cases in that country, two of them fatal. The cases involved a 75-year-old Saudi citizen in Medina who died, a 35-year-old citizen in Medina who is in an intensive care unit, and an 83-year-old citizen who died.
The statement said all three patients had "several chronic diseases" but gave no other details about the cases. No English-language statement was available from the MOH at this writing.
The WHO testing guidance is an update of recommendations released last December. Like the previous version, the new one recommends the use of lower respiratory tract specimens for testing, because they contain the highest viral loads, but adds that upper respiratory tract samples should also be collected whenever possible.
To increase the likelihood of finding the virus, multiple samples from different sites should be collected during the course of the illness, the agency advises. It says there is little information so far on the value of testing whole blood.
The details of several MERS-CoV serologic tests have been published, and the US Centers for Disease Control and Prevention (CDC) has developed a two-stage process for detecting antibodies, according to the WHO. But it adds, "All serological tests developed thus far have been validated only against a small number of convalescent sera from MERS CoV cases and it has not yet been possible to compare the performance of the different assays. No kits are currently available for serological testing."
The guidance recommends that any positive result by a single serologic test should be confirmed with a virus neutralization assay. It says there is no clear consensus on the interpretation of serologic findings in individuals and calls for a cautious approach when confirming cases on the basis of serologic testing.
"For the time being, cases where the testing laboratory has reported positive serologic test results in the absence of PCR [polymerase chain reaction] testing or sequencing, are considered probable cases of MERS-CoV infection, if they meet the other conditions of that case definition," the guidance states.
Sep 18 revised WHO lab testing recommendations
December 2012 WHO testing recommendations
Sep 18 machine-translated Saudi MOH report
Sep 18 Avian Flu Diary post on new cases