Until South Korea abruptly leapt into second place a year ago, the United Arab Emirates had the second highest number of MERS cases in the world, albeit still only a fraction of the number reported in neighboring Saudi Arabia.
While the UAE has reported 83 MERS cases to date, the bulk of their cases appeared during the spring of 2014 (see WHO MERS-CoV Risk Assessment Trip To The UAE) linked to several large outbreaks.
As with Saudi Arabia, we've only seen limited epidemiological data come out of the UAE, although we've seen repeated mention of `mild' or `asymptomatic' cases, suggesting the UAE was casting a wider net than the Saudis in testing contacts of confirmed cases.
A couple of blogs from the spring of 2014 include:
While the risk of MERS transmission from asymptomatic (or mildly asymptomatic) cases has long been a topic of debate, until last year the Saudis didn't even consider them `cases' (see WHO Guidance On The Management Of Asymptomatic MERS Cases).
Like most viral infections, MERS-CoV can produce a wide range of symptoms, and so many mild cases likely go undiagnosed. For a large number of community acquired cases, the source of their infection remains a mystery.
Asymptomatic carriage and transmission offers one plausible, if not proven, explanation (see Study: Possible Transmission From Asymptomatic MERS-CoV Case).
Two years after their last big outbreak we have a detailed look at their epidemiological investigation and the response by HAAD (Health Authority Abu Dhabi), published in the CDC's EID Journal.
As previously suspected, mild and/or asymptomatic patients made up a large percentage of UAE's cases, and these patients were frequently shown to shed the virus for more than 2 weeks.
While this study doesn't answer the question of whether mild or asymptomatic MERS carriers are substantial contributors to the spread of the virus, it does raise additional concerns.
I've reproduced the abstract and a brief excerpt from the summary below, but this long, detailed report is worthy of reading in its entirety.
Response to Emergence of Middle East Respiratory Syndrome Coronavirus, Abu Dhabi, United Arab Emirates, 2013–2014
Farida Ismail Al Hosani1, Kimberly Pringle1Comments to Author , Mariam Al Mulla, Lindsay Kim, Huong Pham, Negar N. Alami, Ahmed Khudhair, Aron Hall, Bashir Aden, Feda El Saleh, Wafa Al Dhaheri, Zyad Al Bandar, Sudhir Bunga, Kheir Abou Elkheir, Ying Tao, Jennifer C. Hunter, Duc Nguyen, Andrew Turner, Krishna Pradeep, Jurgen Sasse, Stefan Weber, Suxiang Tong, Brett L. Whitaker, Lia M. Haynes, Aaron Curns, and Susan I. Gerber
In January 2013, several months after Middle East respiratory syndrome coronavirus (MERS-CoV) was first identified in Saudi Arabia, Abu Dhabi, United Arab Emirates, began surveillance for MERS-CoV. We analyzed medical chart and laboratory data collected by the Health Authority–Abu Dhabi during January 2013–May 2014.
Using real-time reverse transcription PCR, we tested respiratory tract samples for MERS-CoV and identified 65 case-patients. Of these patients, 23 (35%) were asymptomatic at the time of testing, and 4 (6%) showed positive test results for >3 weeks (1 had severe symptoms and 3 had mild symptoms). We also identified 6 clusters of MERS-CoV cases.
This report highlights the potential for virus shedding by mildly ill and asymptomatic case-patients. These findings will be useful for MERS-CoV management and infection prevention strategies.
In summary, our findings of predominance of male MERS-CoV case-patients, development of more severe disease in older case-patients, and clustering in healthcare settings and household settings are consistent with previous reports (12,20).
This descriptive study also highlights demographic, risk factor, and symptom data related to case-patients tested for MERS-CoV in Abu Dhabi. Our study provides further evidence of a long duration of PCR positivity and the value of using lower respiratory tract samples in monitoring MERS-CoV infection.
We also identified asymptomatic and mildly ill MERS-CoV case-patients, which informs practicing clinicians that MERS-CoV causes a wide spectrum of disease.
Finally, our study provided a detailed overview of the unique and comprehensive surveillance and response model for MERS-CoV in Abu Dhabi, which included screening symptomatic and asymptomatic case-patient contacts and collecting detailed epidemiologic data on MERS Co-V case-patients.
Further studies must investigate characteristics of case-patients, the role of virus detected by PCR in virus transmission, and potential MER-CoV spread from mildly ill or asymptomatic patients to clarify, and ultimately stop, MERS-CoV transmission.