Although the number of new MERS cases in the nation’s capital Riyadh has slowed somewhat, we continue to see sporadic cases reported in other regions, often – as in today’s report – without an indication of a source of exposure.
While camel (or camel product) exposure is believed responsible for repeatedly reseeding the virus into the community, it is probably responsible for only a small number of infections. Far more cases occur when hospitals amplify – through inadequate infection control practices - single community-acquired cases into larger nosocomial clusters.
But for a substantial portion of community acquired cases, no known exposure is ever determined.
Testing of contacts of confirmed cases has shown that roughly 20% of those who test positive for the virus are either asymptomatic, or only experience mild symptoms. Whether these mild cases can transmit the virus to others remains uncertain (see Study: Possible Transmission From Asymptomatic MERS-CoV Case).
While mild undetected cases in the community are a plausible – if not proven - source for some of these sporadic community cases, we remain badly hampered by the lack of a well mounted case control study out of Saudi Arabia (see WHO EMRO: Scientific Meeting Reviews MERS Progress & Knowledge Gaps).