Comparative Analysis of Eleven Healthcare-Associated Outbreaks of Middle East Respiratory Syndrome Coronavirus (Mers-Cov) from 2015 to 2017

Bernard-Stoecklin, Sibylle; Nikolay, Birgit; Assiri, Abdullah; Bin Saeed, Abdul Aziz; Ben Embarek, Peter Karim; El Bushra, Hassan; Ki, Moran; Malik, Mamunur Rahman; Fontanet, Arnaud; Cauchemez, Simon; Van Kerkhove, Maria D.

The proportion of asymptomatic secondary cases identified during outbreaks has increased since 2014. There is no evidence to suggest that this represents changes in virus pathogenicity, epidemiology or transmission www.nature.com/scientificreports www.nature.com/scientificreports/ patterns of MERS in recent years. However, the increase in the number of reported asymptomatic cases is hypothesized to be due to earlier detection efforts from more aggressive contact identification and testing during HCA-outbreaks since 2015 as testing policies adopted and implemented by KSA and other countries have changed following the large outbreaks in Jeddah/Riyadh in 2014 3, 41, 54 . In 2017, 40-80% of the laboratory confirmed HCP secondary cases experienced no symptoms and were detected as part of a policy to test all contacts irrespective of symptoms (Table 1) . We believe that the identification of HCP asymptomatic cases, and their subsequent isolation, has had a strong impact on prevent further human to human transmission in health care settings. This is visually demonstrated in Fig. 1C by the outbreak labelled SAU16_2, which included 26 (of 30 www.nature.com/scientificreports www.nature.com/scientificreports/ reported cases) asymptomatic cases. While this is a large number of secondary cases, we argue that the early identification, isolation and recovery of these asymptomatic/mildly symptomatic cases effectively stopped human to human transmission.