Last night’s announcement of a new MERS case in Korea – after a hiatus of 4 days without a reported case – was a disappointing, but hardly unexpected. The incubation period of MERS is estimated to max out around 14 days, and so going four days without a case is not sufficient cause to be popping any champagne corks.
Today the World Health Organization has published a briefing note explaining the process, and the difficulties, of patient contract tracing, and how that effects efforts to bring Korea’s MERS outbreak under control.
The good news for Korea is they have an advantage that Middle Eastern countries do not. They have no known (or even suspected) animal reservoir of the virus, while on the Arabian Peninsula, camels are known carriers and are suspected to continual reseed the virus into the human community.
Still, the spread of MERS – particularly in healthcare facilities - has proven itself pernicious, and very difficult to halt.
Briefing notes on MERS-CoV
1 July 2015
In June 2015, WHO and the Republic of Korea’s Ministry of Public Health and Welfare presented the results of their joint assessment of the MERS outbreak. The assessment led to a series of recommendations, which incorporated specific actions to halt the spread of the virus, including early and complete identification and investigation of all contacts; and robust quarantine/isolation and monitoring of all contacts and suspected cases.
Situation in Korea
To date, a total of 182 MERS-CoV cases, including 33 deaths, have been reported. One of the 182 cases is the case that was confirmed in China. In order to quickly identify and isolate any new cases, contacts for identified cases are monitored for a 14-day period (the incubation period of the virus). Currently, about 2 400 people are being monitored. The vast majority of these are monitored in their homes, while about 700, who were in close contact with a confirmed case, are monitored in a health care facility.
Over 13 500 contacts which had been identified and monitored during this outbreak have finished the 14-day monitoring period with no illness and so are released from further monitoring.
Those in close contact with someone who has MERS-CoV are at higher risk of infection, and of potentially infecting others if they begin to show symptoms. Closely watching such persons for 14 days from the last day of exposure will help that person to get care and treatment and will prevent the further transmission of the virus to others.
This monitoring process is called contact tracing, which can be broken down into three basic steps:
- Contact identification: Once a case is confirmed, contacts are identified by asking about the activities of the case and the activities and roles of the people around the case since onset of illness.
- Contact listing: All persons considered to have had significant exposure should be listed as contacts. Efforts should be made to physically identify every listed contact and inform them of their contact status, what it means, the actions that will follow, and the importance of receiving early care if they develop symptoms. The contact should also be provided with preventive information. In some cases, such as the current MERS-CoV outbreak in Korea, quarantine is required for some contacts, either at home, or in hospital for those with a high risk of severe disease should they be infected (eg persons with co-morbidities).
- Contact follow-up: Follow-up all the listed contacts on a daily basis.
Contact tracing can be particularly challenging for several reasons. First of all, the identification of contacts relies on the patient’s memory. The patient must accurately recall all activities carried out and people contacted since the onset of symptoms. The level of detail required mans that it is possible to miss some contacts. Furthermore, some contacts may inadvertently spread the virus before realizing they are a contact, for example if exposed while in an emergency room of a hospital. Some people may even travel before knowing that they are a contact.
Why are there still new cases?
The transmission of the virus is decreasing significantly in Korea, seen in the decrease in the number of new cases. However, sporadic cases are still being identified, which shows that the risk of transmission has not yet been reduced to zero.
Strengthening of contact tracing procedures is helping to better identify contacts especially at the early stage of the disease when MERS may not be suspected. More stringent measures are now in place to follow each contact; in this current outbreak, people in quarantine are called twice daily to update on their health status. Additional training for health care workers in identifying and managing MERS cases is moving forward. These supplementary measures should help close the current gaps that allow continued transmission.