After a very slow start in the first half of June, yesterday Saudi Arabia announced 2 MERS cases, one of which was of a 49 y.o. woman in critical condition in Riyadh.
Today, it appears that the epidemiological investigation has turned up 5 asymptomatic contacts; 3 household members, and two Healthcare workers.
A year ago, we might not have heard about any of these cases, since Saudi Arabia only began to aggressively test for, and report, asymptomatic cases last fall following criticism from the World Health Organization (see WHO Guidance On The Management Of Asymptomatic MERS Cases).
As a result, we are only now starting to get some real data on the incidence of asymptomatic cases, and the role that those cases may play in spreading the virus.
Like most viral infections, MERS-CoV can produce a wide range of symptoms, and so many mild cases are likely go undiagnosed. For a large number of community acquired cases, the source of their infection remains a mystery.
Asymptomatic carriage and transmission offers one plausible, if not yet proven, explanation (see Study: Possible Transmission From Asymptomatic MERS-CoV Case).