Although Korea was an outlier event, in the short history of MERS in the Middle East, summers have been generally pretty quiet (see ECDC chart below). Cases tend to pick up a bit in the fall and winter, and peak in the spring.
Credit ECDC RRA Report
We do continue to see a trickle of case reports out of Saudi Arabia this summer, with the 12th case reported from the Riyadh region in just over two weeks. While details have been scant, the indications are that much of this uptick in cases has been due to a combination of both community and hospital exposures.
Unlike many of those cases, however, today’s entry is not listed as a contact of a known case.
While many MERS cases have pretty well defined exposure risks (nosocomial, family contact, camels, etc.), often there is no readily apparent source of infection, which has led to speculation that mildly symptomatic cases may be flying under the surveillance radar, and spreading the virus in the community.
In November of 2013, we looked at a study published in The Lancet Infectious Diseases, that attempted to quantify the likely extent of transmission of the MERS virus in the Middle East. (Middle East respiratory syndrome coronavirus: quantification of the extent of the epidemic, surveillance biases, and transmissibility).
They calculated that for every case identified, there are likely 5 to 10 that go undetected.
More recently, last April in the Lancet’s Presence of Middle East respiratory syndrome coronavirus antibodies in Saudi Arabia: a nationwide, cross-sectional, serological study by Drosten & Memish et al., researchers found MERS antibodies in 15 of 10009 serum samples analyzed from across Saudi Arabia. They wrote:
Seroprevalence of MERS-CoV antibodies was significantly higher in camel-exposed individuals than in the general population. By simple multiplication, a projected 44 951 (95% CI 26 971–71 922) individuals older than 15 years might be seropositive for MERS-CoV in Saudi Arabia. These individuals might be the source of infection for patients with confirmed MERS who had no previous exposure to camels.
While a plausible source for some of these unexplained sporadic community infections, we are still badly hampered by the lack of a well mounted case control study out of Saudi Arabia. Last May, in WHO EMRO: Scientific Meeting Reviews MERS Progress & Knowledge Gaps we examined many of the deficits remaining in our understanding of this disease.