A review of asymptomatic and sub-clinical Middle East Respiratory Syndrome Coronavirus Infections.

The epidemiology of Middle East Respiratory syndrome coronavirus (MERS-CoV) since 2012 has been largely characterised by recurrent zoonotic spill-over from dromedary camels followed by limited human-to-human transmission, predominantly in health care settings. The full extent of infection of MERS-CoV is not clear, nor is the extent and/or role of asymptomatic infections in transmission. We conducted a review of molecular and serological investigations through PubMed and EMBASE from September 2012 to 15 November 2018 attempting to measure sub-clinical or asymptomatic MERS-CoV infection within and outside of health care settings. We performed retrospective analysis of laboratory-confirmed MERS-CoV infections reported to the World Health Organization to 27 November 2018 to summarize what is known about asymptomatic infections identified through national surveillance systems. We identified 23 studies reporting evidence of MERS-CoV infection outside health care settings, mainly of camel workers, showing ranges of seroprevalence of 0-67% depending on the study location. We identified 20 studies in health care settings, of health care worker (HCW) and family contacts, of which 11 documented molecular evidence of MERS-CoV infection among asymptomatic contacts. Since 2012, 298 laboratory confirmed cases were reported as asymptomatic to the World Health Organization, 164 of whom were HCW. Viral shedding studies of asymptomatic MERS infections have demonstrated the potential to transmit MERS-CoV to others. Our results highlight the possibility for onward transmission of MERS-CoV from asymptomatic individuals. Screening of HCW contacts of confirmed MERS-CoV patients is currently recommended, but systematic screening of non-HCW contacts outside of health care facilities should be encouraged.