In the Journals

MERS outbreak in Saudi Arabia tied to nosocomial transmission

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November 5, 2014

An outbreak of Middle East respiratory syndrome coronavirus in Jeddah and Riyadh, Saudi Arabia, in the spring appears to have been largely transmitted through human-to-human contact in hospitals, according to recent findings.

In a study published in Clinical Infectious Diseases, researchers sought to identify the cause of a sudden increase in MERS infections in Jeddah earlier this year. Hypotheses were formulated to explain the outbreak pattern, and included the following: increased zoonotic transmission, nosocomial transmission, increased surveillance, changes in viral transmissibility and diagnostic laboratory artifacts.

The researchers analyzed diagnostic information gleaned from Jeddah Regional Laboratory, including virus samples from the Jeddah outbreak and viruses occurring simultaneously in Riyadh, Al-Kharj, and Madinah. The researchers partially or fully sequenced the viruses, and a set of four single nucleotide polymorphisms unique to the Jeddah outbreak were identified. Viruses from Jeddah and Riyadh were isolated and evaluated in cell culture.

Of the 168 samples that tested positive from the Jeddah outbreak, 49% could be traced back to King Fahd Hospital. Viruses from Jeddah were found to be monophyletic and similar; viruses from Riyadh, however, were paraphyletic and disparate. The Riyadh cases were linked with a hospital-associated transmission cluster that also included cases in the United States and the Netherlands. One virus of the Jeddah type was identified in Riyadh, and could be traced to travel history to Jeddah. The virus isolates from both locations did not differ from the coronavirus EMC/2012 in replication, escape of interferon response, or serum neutralization. There was no significant change during the Jeddah outbreak in detection rates and average virus concentrations.

“Our investigations suggest a predominance of human-to-human transmission during the Jeddah outbreak without evidence for modification of viral shedding, replication, and immune escape,” the researchers wrote. “A coincident increase of cases in Riyadh was the result of multiple, independent sources with some phylogenetic evidence of nosocomial spread. Contact tracing by RT-PCR should be restricted to defined groups of patients to avoid an overload on the health care system.”

Disclosure: One of the researchers is the CEO of TIB Molbiol, a company providing some of the RT-PCR reagents used in the study.

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