Middle East Respiratory Syndrome (MERS) outbreaks associated with nosocomial infection and human-to-human transmission have been routinely documented since the first cases were first reported in 2012. At least 11 major MERS outbreaks have occurred since then, including the current outbreak in Riyadh, Saudi Arabia.
All the major MERS outbreaks have occurred on the Arabian Peninsula with the exception of a recent outbreak in the Republic of Korea between May and June, 2015 where more than 180 cases could be traced back to a single index case infected on the Arabian Peninsula. With the exception of data from the Republic of Korea outbreak, detailed information is limited on the MERS outbreaks on the Arabian Peninsula.
One or possibly two separate outbreak in the United Arab Emirates included as many as 40 cases between April and May 2014 from Abu Dhabi and Al Ain. All of the remaining major outbreaks from the Arabian Peninsula occurred in Saudi Arabia.
Chronologically, the first major outbreak in Saudi Arabia occurred at Al Hofuf between April and May of 2013 with about 20 cases. Shortly thereafter, another outbreak started in Riyadh in July 2013 and continued for several months. Perhaps as many as 45 individuals were infected in this outbreak. Riyadh again experienced another outbreak with more than 140 cases between February and May of 2014. About this same time, from March through April 2014, more than 200 individuals were reported from a MERS outbreak in Jeddah. Between April and May 2014, separate outbreaks were reported from both Mecca and Madinah with about 30 cases each. Between October and December 2014, Taif experienced a MERS outbreak with at least 25 individuals.
In early 2015 between January and March, an outbreak including at least 60 cases was reported from Riyadh. Between April and June 2015, a MERS outbreak in Al Hofuf resulted in about 40 human infections. Riyadh began experiencing the latest MERS outbreak in July 2015 which is still continuing.
The Riyadh region has experienced the greatest concentration of MERS cases in the world. Since October 2012, there have been 4-5 separate MERS outbreaks among the more than 400 publicly reported cases from Riyadh (see chart). Many of these cases are a result of human-to-human transmission.
These outbreaks are similar in nature. Some infections results from contact with confirmed cases or occurred in a health setting. These outbreaks also included infected healthcare workers.
Based on reports by the Saudi Arabia Ministry of Health and the World Health Organization (WHO), the index case for the current outbreak in Riyadh appears to a 56-year-old male who experienced onset on July 13. He is reported to have frequent contact with camels and consumed raw camel milk. Shortly thereafter, several of his family members, including his wife and son became infected. As this outbreak grew, hospitalized individuals being treated in the same facility as confirmed patients would become infected. Other individuals became infected after seeking treatment for unrelated medical conditions or visiting healthcare facilities where existing MERS cases were being treated. A number of cases trace their infection back to contact with confirmed cases. The distinctive feature of these outbreaks is that they are associated with healthcare facilities where healthcare workers are routinely reported to be infected. Infected healthcare workers are a clear signal of human-to-human transmission during an outbreak.
Through August 28, 2015, more than 110 individuals have been infected with MERS in Riyadh during this outbreak. An epi curve (see below) of the current MERS cases from Riyadh suggests that the outbreak is being contained. The graph compares a 4-day moving average of the number of daily cases reported from Riyadh by the Saudi Arabia Ministry of Health with the 4-day moving average of the distribution of onset dates (posted by WHO) for the reported cases. Because onset dates are not reported by the Saudi Arabia Ministry of health there is a time lag between the initial posting of the cases, and the reporting of onset dates. The declining trend in the number of cases being reported from Riyadh by the Saudi Arabia Ministry of Health suggests this outbreak is being contained and may be over shortly.