The household/hospital cluster of MERS cases in Wadi Al Dawasir - which we've been following for several days - continues to expand (see this morning's post MERS-CoV: Wadi Al Dawasir Hospital Cluster Grows for more background), with the addition of an asymptomatic healthcare worker today.
This is the 8th case reported from Wadi Al Dawasir in less than a week.
A second case, with camel contact, is also announced today from Al Qunfudhah.
While we've long known that some people can be infected with the MERS coronavirus without showing symptoms, we don't have a very good handle on how often that happens, or if these people can pass the virus on to others.
Since a substantial number of community acquired cases have no apparent risk exposure (to camels, health care facilities, or known MERS cases), this has led to speculation that limited community transmission via asymptomatic or mild carriers may be occurring.
In 2015's EID Journal: Risk Factors For Primary MERS-CoV Infection, Saudi Arabia, researchers found camel exposure to be a significant factor but also noted:
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.
Last summer we saw a large hospital outbreak (see Saudi MOH On KKUH MERS Outbreak & Increased Asymptomatic Detections) in Riyadh, which involved at least 28 patients - 21 of whom were asymptomatic - an unusually high ratio by any standard.
Unfortunately we are getting far fewer details of late, as the Saudi's CCC weekly monitor - which for almost a year provided us with much appreciated insight on KSA's MERS outbreaks - hasn't been updated in almost 7 months (last edition Volume 2 - Issue 32- Tuesday, August 16, 2016).