The Riyadh hospital cluster continues to expand, albeit primarily due to asymptomatic contacts testing positive for the MERS Coronavirus.
As discussed two days ago, asymptomatic cases have been more frequently reported by KSA since 2016, possibly due to more comprehensive testing of contacts.
Previously thought to comprise only about 10% of cases, over the past year we've seen a few nosocomial outbreaks that are 50% or more asymptomatic (see Saudi MOH On KKUH MERS Outbreak & Increased Asymptomatic Detections).
Today's report adds 5 new cases to the Riyadh outbreak, 4 of which are listed as asymptomatic.
This raises to 20 the number of cases reported from Riyadh over the past week, with 14 of those listed as asymptomatic. We've no information about the chains of infection, or even solid information on who was the index case.
Since contact tracing and testing is easier in a hospital environment, it makes sense that most of the asymptomatic cases we learn about come from hospital exposures.
Unknown are how many undetected mild and/or asymptomatic cases there are in the community, and how much of a role - if any - they play in the spread of the virus.