Although cases remain sporadic, we have the 4th `primary' case (without a known risk exposure) reported this week from Buraidah. Curiously, all are `older' females (63, 88, 87, 70).
This may all be a coincidence, but primary MERS cases generally skew heavily towards older men.
Although many community acquired or `primary' MERS cases are known to have camel contact (a presumed high risk), most do not, leaving how and where these cases were exposed unresolved.
Like most viral infections, MERS-CoV can produce a wide range of illness, and so it is likely that many mild or asymptomatic cases go undetected. A year ago, a study in the EID Journal: Risk Factors For Primary MERS-CoV Infection, Saudi Arabia, while finding camel exposure a major risk factor, wrote:
Other potential explanations of MERS-CoV illness in primary case-patients who did not have direct contact with dromedaries include unrecognized community exposure to patients with mild or subclinical MERS-CoV infection or exposure to other sources of primary MERS-CoV infection not ascertained in our study.For now, the role of mild or asymptomatic cases in spreading the virus remains suspected, but largely unproven.