WHO Risk Assessment: MERS-CoV (April 24th, 2014)

 

Coronavirus – Credit CDC PHIL

 

 

# 8525

 

The World Health Organization has released an updated Risk Assessment on the MERS coronavirus, which is available in PDF format on their Coronavirus Infections page.  I’ve only posted some extended excerpts, download the full pdf file to read it in its entirety.

WHO RISK ASSESSMENT

Middle East respiratory syndrome coronavirus (MERS‐CoV)
24 April 2014

Summary of available information

Since April 2012, 254 laboratory-confirmed cases of human infection with Middle East respiratory syndrome coronavirus (MERS‐CoV) have been reported to WHO, including 93 deaths. To date, reporting countries in the Middle East include Jordan, Kuwait, Oman, Qatar,Kingdom of Saudi Arabia (KSA) and the United Arab Emirates (UAE); in Europe: France,Germany, Greece, Italy and the United Kingdom (UK); in North Africa: Tunisia; and in Asia:Malaysia and the Philippines.

The occurrence of new cases seems to follow a seasonal pattern, with increasing incidence from March-April onwards. The number of cases sharply increased since mid-March 2014, essentially n KSA and UAE, where two important healthcare-associated outbreaks are occurring.

As much as 75% of the recently reported cases appear to be secondary cases, meaning that they are considered to have acquired the infection from another ifected person. The majority of these secondary cases are mainly healthcare workers who have been infected within the healthcare setting, although several patients who were in the hospital for other reasons are also considered to have been infected with MERS‐CoV in the hospital. The majority of the infected healthcare workers presented with no or minor symptoms. Only four instances of transmission within households have been reported, and no large family cluster has been identified. When human‐to‐human transmission occurred, transmission was not sustained, and to date only two possible tertiary cases have been reported.

The number of cases who acquired the infection in the community has also increased since mid-March. These cases have no reported contacts with other laboratory confirmed cases, and some have reported contacts with animals. Although camels are suspected to be the primary source of infection for humans, the exact routes of direct or indirect exposure remain unknown.

Investigations to identify the source of infection and routes of exposure are still ongoing.Several of the recent cases acquired the infection in KSA or UAE and then travelled to another country, including Greece (1 case), Jordan (1 case), Malaysia (1 case), and the Philippines (1 case). No further transmission has been documented so far. Of note, exported cases occurred in the past that resulted in limited further human‐to‐human transmission (France and UK).

In view of the increasing number of cases – in particular secondary cases, nosocomial outbreaks and exported cases – the WHO risk assessment has been revisited to determine whether transmission pattern has changed and whether sustained community transmission is occurring.

Risk assessment
This risk assessment is based on currently available data and knowledge, and will be updated as more information is made available. The investigations are still ongoing and new findings on, for example, exposures to animal and/or environmental source, transmission chains, risk factors for infection among primary cases and healthcare workers, and serological investigations will be critical to make the risk assessment more robust.

Has the transmission pattern of MERS-CoV changed?

The majority of the cases now reported have likely acquired infection through human‐to‐human transmission and only about a quarter are considered as primary cases, which suggests slightly more human‐to‐human transmission than previously observed.

One hypothesis is that the transmission pattern and transmissibility have not changed and that the occurrence of two large nosocomial outbreaks reflects inadequate infection prevention and control measures, coupled with intensive contact tracing and screening. Several elements would support this hypothesis: i) the clinical picture appears to be similar to what was observed earlier; secondary cases tend to present with a milder disease than that of primary cases;
however, we note that many secondary cases have been reported as asymptomatic; ii) only 2 possible tertiary cases have been reported; iii) the recent exported cases did not transmit further; iv) screening of contacts revealed very few instances of household transmission; and v) no increase in the size or number of household or community clusters has been observed.

An alternative hypothesis is that transmissibility of the virus has increased and is resulting in more human‐to‐human transmission as the basis for the recent upswing in cases. It is possible that current levels of surveillance are missing cases of mild infection within the community. At this point, there is insufficient information on the recent cases to definitively exclude these hypotheses.

Can we expect additional cases of MERS‐CoV infection in the Middle‐East countries?

The way humans become infected from an animal and/or environmental source is still under investigation. More individuals are likely to be infected until the mode of transmission is determined and preventive measures implemented to break transmission from the source to humans. For the third consecutive year, the number of cases increase in March‐April and it is very likely that more primary cases will occur, and consequently further transmission will occur.

Can we expect additional cases exported to other countries and further transmission?

It is very likely that cases will continue to be exported to other countries, through tourists, travellers, guestworkers or pilgrims, who might acquire the infection following an exposure to the animal or environmental source, or to other cases, in a hospital for instance. Whether these cases will further transmit will depend of the capacity of the receiving country to rapidly detect, diagnose and implement appropriate infection prevention and control measures. Of note, further transmission from exported cases did occur in the past, but transmission was not sustained.

(Continue . . . )