Saudi MOH: Riyadh Cluster Grows By Another 5 Cases

#12,527

Riyadh's (mostly) hospital acquired MERS outbreak continues, with 5 more cases announced today. While spreading at an impressive rate, the good news is most of the cases are reported to be asymptomatic.

Today's report adds 4 asymptomatic cases (a mixture of HCWs & patients) and 1 symptomatic case, a 25 y.o. male HCW in stable condition.

Of the 25 Riyadh cases reported over the past week, 18 are listed asymptomatic. We've no specifics about the epidemiology of this event, and as a reader asked yesterday, we don't really have a way to know if any of the `asymptomatic' cases reported previously have gone on to develop symptoms.

The size of this outbreak suggests it may involve one or more `super spreaders', as we've previously seen in South Korea, and last year in Saudi MOH: KKUH Hospital Outbreak As A `Superspreading' Event.

With more than 2/3rds of the cases in the cluster reported as asymptomatic, this outbreak once again raises questions about how many undiagnosed community cases are missed by surveillance.


We've previously looked at estimates that have suggested the number of MERS cases far exceeds the numbers reported by countries on the Arabian Peninsula.   

• In November of 2013, we looked at a study published in The Lancet Infectious Diseases, that estimated for every case identified, there are likely 5 to 10 that go undetected.
• In 2015 when Saudi Arabia had recorded fewer than 1200 MERS cases, a seroprevalence study(see Presence of Middle East respiratory syndrome coronavirus antibodies in Saudi Arabia: a nationwide, cross-sectional, serological study by Drosten & Memish et al.,) suggested nearly 45,000 might have been infected. 
• And last year, in EID Journal: Estimation of Severe MERS Cases in the Middle East, 2012–2016, we saw a study that suggested the number of severe cases is 2.3-times higher than the total number of all laboratory-confirmed cases combined (including mild and asymptomatic) cases in the region.

Since the source of many community acquired cases remains unknown, asymptomatic carriage and transmission offers one plausible - if not yet proven - explanation (see Study: Possible Transmission From Asymptomatic MERS-CoV Case).

The post-mortem analysis on this outbreak ought to make for very interesting reading, if and when we get to see it.