The Saudi MOH is reporting another asymptomatic MERS case - the 4th case in a week - from Wadi Al Dawasir, which was the site of a household/hospital cluster of cases during the first half of March.
Today's case involves a 26 y.o. male who is described as a `secondary household contact'. On April 21st, KSA reported 3 additional asymptomatic cases, 1 listed as a `secondary Healthcare Acquired HCW', and the other two as `secondary household contacts'.
No dates are provided for these cases, and we've not seen a WHO update since April 3rd (covering cases Feb 23rd - March 16th), so it isn't immediately apparent whether all of these are `new' cases, or if some are belated discovery (or reporting) of cases from the March outbreak.
Adding to the mystery, on April 19th we saw the Saudi MOH Announce A Primary MERS Case In Wadi Al Dawasir. No risk exposure was provided.
Of the 10 original cases reported in March from Wadi Al Dawasir, 2 were listed as `Under Review' (possibly household members), 4 were listed as `Secondary Hospital Acquired (patients)', 2 are described as `Secondary Household contacts', and 2 were listed as HCWs. Of these 10, 3 were listed as `asymptomatic'.
This week's reports bring that total to 8 asymptomatic cases - or roughly 50% of the cases reported from Wadi Al Dawasir since early March.Prior to 2016, the assumption was (based on very limited contact testing by the Saudis), that only about 10% of MERS cases were asymptomatic (or mildly ill). Recent testing has suggested that number may be low.
Following unusually candid (and public) criticism of the Saudi's lack of testing and reporting of asymptomatic cases (see Sept 2015 WHO Statement On The 10th Meeting Of the IHR Emergency Committee On MERS), we've seen a significant jump in the number of asymptomatic cases reported.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 cases - 21 (75%) of whom were asymptomatic.
Since contact tracing and testing is much easier in a hospital environment, it makes sense that nosocomial outbreaks would reveal a higher rate of asymptomatic infection.Unknown are how many undetected mild and/or asymptomatic cases there are in the community, and how much of a role - if any - they may play in the spread of the virus.