Epidemiological update: Middle East respiratory syndrome coronavirus (MERS-CoV)

Epidemiological update

​​By 22 November 2013, 160 cases of MERS have been reported. All cases have either occurred in the Middle East or have direct links to a primary case infected in the Middle East.

​In June 2012, a case of fatal respiratory disease in a previously healthy 60-year-old man was reported from Saudi Arabia [1]. The cause was subsequently identified as a new coronavirus that has been named Middle East respiratory syndrome coronavirus (MERS-CoV). By 22 November 2013, 160 cases of MERS have been reported. All cases have either occurred in the Middle East or have direct links to a primary case infected in the Middle East. From the Middle East, Saudi Arabia has reported 130 cases, including 55 deaths, Jordan two cases, including two deaths, Qatar seven cases, including three deaths, the United Arab Emirates six cases, including two deaths. During the second week of November 2013, two new places from the Middle East have acknowledged cases. Oman (reported one case, which died) and Kuwait (reported two cases, without any deaths). Twelve cases were reported outside of the Middle East in the United Kingdom (4), Italy (1), France (2), Germany (2), and Tunisia (3). The primary case for each chain was infected in the Middle East, and local secondary transmission following importation was reported from the United Kingdom, France, and Tunisia. Two probable cases [2]  were recently reported from Spain [3] , the first case was reported on 4 November 2013, and the second case was reported on the 14 November. Both cases have travel history to Saudi Arabia. The first case was symptomatic on the flight from Saudi Arabia to Spain. These probable cases tested positive by the first screening test. Further confirmatory testing is on-going [4]. Probable cases with inconclusive test results have previously been reported from France [5] and Italy [6].

Figure 1. Distribution of confirmed cases* of MERS-CoV by month of onset and probable place of infection, March 2012 – 22 November 2013 (n=160**)

Figure 2. Distribution of confirmed cases of MERS-CoV by reporting country, March 2012 – 22 November 2013 (n=160)

As of 22 November 2013, the case-fatality ratio is 43 % and is increasing with age. The male to female ratio is 2:1. Among the 155 cases with known age, the median age was 52 (IQR 39-64) and 142 (91.6%) were older than 19 years. We classified cases as primary or secondary based on the information provided publicly by WHO and KSA MOH. Primary cases were classified using the following criteria: no reported exposure to other known cases, occurring in an area with no cases close in time and/or reported as primary case in a cluster. Secondary cases were classified based on the epidemiological link to other confirmed cases. Thirty-seven cases could not be classified based on the information available and they were left out from the analysis.

Figure 3. Distribution of confirmed cases of MERS-CoV by primary (N=39) and secondary cases (N=83) by gender and age group, March 2012 - 22 November 2013

*Among secondary cases, 3 cases were not included in the analysis due to unknown age.
Thirty-nine cases were classified as primary cases and of these, 79.5% (31/39) were male with a median age of 59 years (Table 1). The male to female ratio of 3.9 among primary cases is significantly differing from an even gender distribution (p=<10-3), reflecting potentially a gender related difference in exposures. Among the 83 secondary cases with documented age and sex, the median age is 45 years and the sex distribution does not significantly differs from an even distribution (p=0.44), with 38 (45.8%) cases being females. The more even male to female ratio of 1.2 among secondary cases, can be explained by the enhanced surveillance systems in tracing close contacts of the confirmed cases.
 Table 1. Epidemiological characteristics of confirmed cases of MERS-CoV comparing primary (N=39) and secondary cases (N=83), March 2012 - 21 November 2013.

Epidemiological characteristics Primary cases Secondary cases P value
n=39 (%) n=85 (%)
Gender 0.004a
  Male 31 (79.5) 45 (54.2)
  Female 7 (17.9) 38 (45.8)
  Unknown - 2
Outcome 0.003 a
  Dead 23 (59.0) 25 (29.4)
  Alive 16 (41.0) 60 (70.6)
Comorbidities b <0.001 a
  Yes 27 (90.0) 39 (50.6)
   No 3 (10.0) 38 (49.4)
   Unknown 9 8
Nosocomial transmission <0.001 a
  Yes 2 (5.7) 38 (50.7)
  No 33 (94.3) 37 (49.3)
  Unknown 4 10

a Two-tailed Fisher’s exact test (unknown cases were excluded from the statistical analysis). b Comorbidities including, among others, diabetes, hypertension, chronic cardiac and chronic renal disease.
 
Several recent cases in the Arabian Peninsula have reported camel or animal exposures. The significance of this finding is unclear at the moment. New sporadic cases continue to be detected in the Arabian Peninsula, occasionally giving rise to clusters. One of the recent confirmed cases owned a camel that subsequently tested positive by PCR for MERS-CoV by the screening test [7], this may provide some additional evidence of possible role of zoonotic transmission for this severe disease.
The WHO MERS-CoV research group has recently reviewed and summarised the state of knowledge and data gaps regarding MERS-CoV [8]. The analysis presented in this epidemiological update support their conclusions. Slight differences in the results are due to a difference in classification of cases into primary and secondary cases, and inclusion of new cases in our analysis. The epidemiology, virology, phylogeny and emergence of MERS-CoV were reviewed by the research group in order to inform public health policies. The group concluded that “sustained human-to-human transmission of MERS-CoV has not been observed. Outbreaks have been extinguished without overly aggressive isolation and quarantine suggesting that transmission of virus may be stopped with implementation of appropriate infection control measures” [8]. WHO has also published a Middle East respiratory syndrome coronavirus (MERS-CoV) summary and literature update – as of 22 November 2013 on the Global Alert and Response website [9].
ECDC continues to monitor information on the situation on MERS-CoV worldwide, in the light of these new developments. The assessment provided in the ECDC rapid risk assessment (RRA) on the 6 November 2013 remains valid [10].