The Saudi MOH was offline yesterday when I checked for their MERS update, so today's update is for both today and yesterday. As it turns out, today's case is an asymptomatic household contact of yesterday's Primary case from Mecca.
Since they show no symptoms, the only time we tend to see asymptomatic cases reported is when they are tested as contacts to known cases. How often people are infected asymptomatically (or mildly) and are not picked up by surveillance is unknown.
Also unknown is whether, or how efficiently, asymptomatic cases can spread the virus, although it is assumed possible.
Until last year the Saudis didn't even consider them `cases', rarely isolated them, and inconsistently reporting them to the WHO (see WHO Guidance On The Management Of Asymptomatic MERS Cases).
Given the number of primary MERS cases without a known source of infection, determining the incidence, and risk from, asymptomatic cases remains an important goal.