Case characteristics among Middle East respiratory syndrome coronavirus outbreak and non-outbreak cases in Saudi Arabia from 2012 to 2015

Alhamlan, F S; Majumder, M S; Brownstein, J S; Hawkins, J; Al-Abdely, H M; Alzahrani, A; Obaid, D A; Al-Ahdal, M N; BinSaeed, A

Using the Saudi MOH CCC public health data set on MERS cases reported to have occurred from September 2012 to September 2015, we found three factors distinguishing outbreak and non-outbreak cases: (1) patients older than the mean age of 51 years represented a larger than expected fraction of outbreak than of nonoutbreak cases, (2) nosocomial infections occurred much more frequently among outbreak cases than among non-outbreak cases and (3) patients infected during outbreaks were more likely to die of MERS-CoV infection than those infected during non-outbreak conditions (table 2). Given that age was associated with death, it is worth noting that the third factor may be explained in part by the over-representation of older individuals among the outbreak cases. Although age was also associated with gender, we found that the proportion of MERS-CoV infections in men was approximately two-thirds for outbreak and non-outbreak cases (table 2) . However, the general over-representation of men is consistent with many previous studies showing predominantly male patients with MERS-CoV. 3 16 17 Our results also showed that healthcare workers comprised 22% of all Saudi MERS cases diagnosed up to October 2015 (table 2) . This percentage is in agreement with a 2014 WHO report stating that 109 of the 402 (∼25%) reported MERS-CoV infections in the Jeddah (Saudi Arabia) 2014 outbreak occurred in healthcare workers. 16 Areas neighbouring Saudi Arabia, including the city of Al-Ain in the United Arab Emirates, also reported MERS-CoV infections in 16 healthcare workers out of 23 total cases. 17 Additionally, during the large Figure 3 Histogram of the time from disease onset to MERS-CoV confirmation for outbreak and non-outbreak cases. Average time from onset to confirmation was 6.6 days for outbreak cases and 11.9 days for non-outbreak cases. South Korean outbreak in 2015, 14% of the infected cases were in healthcare workers. 5 Another 2014 WHO report stated that most person-to-person MERS-CoV infections likely occurred in healthcare settings. 18 We found that nosocomial transmissions comprised one-third of all Saudi MERS-CoV cases reported to date. Importantly, these nosocomial infections occurred more frequently in outbreak cases than in non-outbreak cases, suggesting that nosocomial infections fuelled outbreaks (table 2). The first outbreak in Al-Hasa, Saudi Arabia, (2013) provided valuable information about MERS-CoV transmission in a healthcare setting. The outbreak started in a haemodialysis unit of a private hospital in Al-Hasa, but subsequently spread to three other hospitals. Phylogenetic analysis of the outbreak showed that only eight of the epidemiological transmissions were related, indicating multiple zoonotic introductions of MERS-CoV. 18 To date, MERS-CoV has been detected in camels from Saudi Arabia, Oman, Qatar, Jordan and Kenya, 7 8 10 19 20 and it has been shown that humans can acquire MERS-CoV directly from dromedary camels. 21 Since camel exposure data (ie, whether the patient owned or raised camels) were gathered for only 204 of the 1250 cases in the database used by this study, we did not include this information in table 2. Nonetheless, we found that 17% of the 123 non-outbreak cases and 10% of the 81 outbreak cases reporting data on camel exposure indicated that the patients owned or raised camels. Although this difference was not statistically significant, this result suggested that camel exposure, and thus zoonotic transmission, migh