|Credit Saudi CCC|
For much of the month of June we followed the outbreak at Riyadh's KKUH (King Khalid University Hospital) which spiraled to more than 2 dozen cases (see Saudi MOH On KKUH MERS Outbreak & Increased Asymptomatic Detections).
Of the 28 cases from the KKUH outbreak, 21 were listed as being either very mild or asymptomatic. An unusually high ratio by any standard.
Today the Saudi National Command & Control Center (CCC) is back with another review of that outbreak, this time focusing on what they describe as a `super-spreading' event.
We've seen other large hospital outbreaks attributed to `super spreading' events (see The Lancet: Mapping The Korean MERS-CoV Superspreading Event).
While some infected patients do shed more virus than others (see Influenza Transmission, PPEs & `Super Emitters’), it generally takes more than a highly infectious patient to spark an event. According to Stein’s excellent 2011 review Super-spreaders in infectious diseases:
Super-spreading events are shaped by host, pathogen, and environmental factors. Often, more than one factor may be implicated in the same outbreak.
Although today's Weekly Monitor Report from the Saudis places the KKUH outbreak in the `superspreading' category, it provides relatively few details. Hopefully a more detailed epidemiological report is in the works.
Volume 2 Issue 29 Tuesday 26 July 2016
MERS Super-Spreading events
The recent outbreak of MERS reported from a university hospital raised the possibility of having a super-spreading events resulting in a larger outbreak.
Super-spreading events were strongly suspected considered in some MERS outbreaks. Certain MERS infected individual may transmits an infection disproportionately to more susceptible contacts, possibly because of increased viral load, heavy respiratory secretions, than the average infected individual.
Super-spreading events constitute the presence of those “highly infectious” individuals in crowded areas like emergency rooms in contact with other patients, healthcare workers and environment. Such events can cause large outbreaks similar to the outbreak in South Korea last year.
During the outbreak of Korea, majority of MERS transmission were linked to super-spreading events. Similarly, the recent nosocomial MERS outbreak in Riyadh (2016) was probably related to a super-spreading event (Figure 1).
This was also observed in the outbreak of 2013 in Al-Ahsa. Mis-diagnosis or late diagnosis due to co-infection with another pathogen and/or immunosuppression are one of the facets in super-spreading incidents along with individual variation in infectivity and the number of contacts.
It is self-evident, however, that other factors played a role in these incidents. Super-spreading events tied to nosocomial outbreaks of MERS have been attributed in part to suboptimal infection prevention and control (IPC) measures, overcrowded emergency departments (ED), limited isolation rooms in EDs and inadequate ventilation, delayed hospital admission, interhospital transfers, and/or poor communication between healthcare facilities (HCFs).
Super-spreader events are key to amplify nosocomial transmission of MERS and support the Region adoption of IPC precautions particularly in treatment rooms.
It is important to identify such highly infectious individuals and super spreading events through full investigation of the transmission pathways from a single index case to secondary cases in HCFs.
Rapid case detection and strict adherence to IPC Eastern Region measures, which can rapidly reduce the risk of super-spreading events and therefore the size of the nosocomial outbreaks.
Predicting and identifying super-spreaders open significant medical and public health challenges, and represent important aspects of infectious disease management and emergency preparedness plans.
Generally, the key to prevent large outbreaks of emerging infectious diseases is through complete preparedness in HCFs and proper collaboration between health and other governmental agencies.
Super spreading events aren’t limited to SARS and MERS, as they have also been documented with measles, HIV, TB, S. aureus, Ebola, and various STDs . . .among others (cite).
While the host and the pathogen are important parts to the equation, the lesson in South Korea is environment and opportunity play huge roles in exacerbating these super spreader events.
Beyond exposure to a highly infectious host, just last April the Saudi MOH identified a number of other factors behind many of these large hospital outbreaks.
Many of MERS outbreaks originated in the Emergency Department (ED). Almost all MERS outbreaks in HCFs stemmed from one or more of the following factors:
- Inadequate awareness of physicians to the case definition of MERS;
- insufficient adherence to Infection Prevention and Control (IPC) practices and procedures especially during Aerosol Generating Procedures (AGP), by not wearing proper Personal Protective Equipment (PPE), or performing AGP in rooms with no negative pressure; inadequate implementation of respiratory triaging of cases;
- discharge against medical advice and inadequate communication of such incidents;
- gaps and flaws in the referral mechanism of MERS cases;
- overcrowded ED and irregular control of entrances;
- and inadequate control of visitation.
A reminder that - while we can't control the infectivity of patients walking into the emergency room - we can reduce a hospital's ability to spread the virus once they arrive.
For more on what that may take, you may wish to revisit TFAH Issue Brief: Preparing The United States For MERS-CoV & Other Emerging Infections.