Friday, August 28, 2015

Case Details from the Current MERS Outbreak in Riyadh Saudi Arabia, August 2015

The current outbreak in Riyadh started mid-July when a 56-year-old man became infected with Middle East Respiratory Syndrome coronavirus (MERS). This individual had frequent contacts with camels and consumed raw camel milk. This man infected his 52-year-old wife, his 53-year-old brother, and 30-year old son. The index case and his wife are reported to have died.

Almost 120 cases have been confirmed during this MERS outbreak in Riyadh through August 28, 2015.  As in other MERS outbreaks, more males then females are infected, about 61%. The males range in age from 2-109 years old with a median age of 61. The females range in age from 25 to 98 with a median age of 58.

The fatality rate for this outbreak is about 25%, with similar death percentages for both males and females. However the fatality statistics could change because the Saudi Arabia Ministry of Health is reporting that there are at least 50 cases still under treatment.

In this outbreak, most of the infections had been contracted by either visiting or being treated in a hospital with current MERS patients. A few cases are reported to have contact with confirmed MERS patients possibly outside of a healthcare setting. Information on family clusters is not available. It is difficult to assess the extent of family clusters, since that information is not generally available. 

Besides the initial family cluster in this outbreak, one other possible family cluster can be proposed from the data. A 56-year-old female experienced symptom onset on August 7, with her death reported on August 17. The World Health Organization reports that a 28-year-old female had contact with this woman and became symptomatic on August 12. A third individual, a two-year-old boy, also had contact with this woman and became symptomatic on August 12 as well. The boy is reported by the Saudi Arabia Ministry of Health to have recovered. Speculating, this cluster would seem to be a result of a daughter and a grandson interacting with the 56-year-old grandparent.

Healthcare workers represent about 11% of all infected individuals in this current outbreak.  This is similar to the overall percentage of healthcare workers infected with MERS in Riyadh since 2012. About 10% of all of MERS cases reported from Riyadh since 2012 were healthcare workers.

The epidemiological similarities among various MERS outbreaks should begin to provide a framework for understanding and controlling this disease in the future.

The Status of the Current MERS Outbreak in Riyadh, Saudi Arabia

Middle East Respiratory Syndrome (MERS) outbreaks associated with nosocomial infection and human-to-human transmission have been routinely documented since the first cases were first reported in 2012. At least 11 major MERS outbreaks have occurred since then, including the current outbreak in Riyadh, Saudi Arabia.

All the major MERS outbreaks have occurred on the Arabian Peninsula with the exception of a recent outbreak in the Republic of Korea between May and June, 2015 where more than 180 cases could be traced back to a single index case infected on the Arabian Peninsula. With the exception of data from the Republic of Korea outbreak, detailed information is limited on the MERS outbreaks on the Arabian Peninsula.

One or possibly two separate outbreak in the United Arab Emirates included as many as 40 cases between April and May 2014 from Abu Dhabi and Al Ain. All of the remaining major outbreaks from the Arabian Peninsula occurred in Saudi Arabia.

Chronologically, the first major outbreak in Saudi Arabia occurred at Al Hofuf between April and May of 2013 with about 20 cases. Shortly thereafter, another outbreak started in Riyadh in July 2013 and continued for several months. Perhaps as many as 45 individuals were infected in this outbreak. Riyadh again experienced another outbreak with more than 140 cases between February and May of 2014. About this same time, from March through April 2014, more than 200 individuals were reported from a MERS outbreak in Jeddah. Between April and May 2014, separate outbreaks were reported from both Mecca and Madinah with about 30 cases each. Between October and December 2014, Taif experienced a MERS outbreak with at least 25 individuals.

In early 2015 between January and March, an outbreak including at least 60 cases was reported from Riyadh. Between April and June 2015, a MERS outbreak in Al Hofuf resulted in about 40 human infections. Riyadh began experiencing the latest MERS outbreak in July 2015 which is still continuing.

The Riyadh region has experienced the greatest concentration of MERS cases in the world. Since October 2012, there have been 4-5 separate MERS outbreaks among the more than 400 publicly reported cases from Riyadh (see chart). Many of these cases are a result of human-to-human transmission.

These outbreaks are similar in nature. Some infections results from contact with confirmed cases or occurred in a health setting. These outbreaks also included infected healthcare workers.

Based on reports by the Saudi Arabia Ministry of Health and the World Health Organization (WHO), the index case for the current outbreak in Riyadh appears to a 56-year-old male who experienced onset on July 13. He is reported to have frequent contact with camels and consumed raw camel milk. Shortly thereafter, several of his family members, including his wife and son became infected. As this outbreak grew, hospitalized individuals being treated in the same facility as confirmed patients would become infected. Other individuals became infected after seeking treatment for unrelated medical conditions or visiting healthcare facilities where existing MERS cases were being treated. A number of cases trace their infection back to contact with confirmed cases. The distinctive feature of these outbreaks is that they are associated with healthcare facilities where healthcare workers are routinely reported to be infected. Infected healthcare workers are a clear signal of human-to-human transmission during an outbreak.

Through August 28, 2015, more than 110 individuals have been infected with MERS in Riyadh during this outbreak. An epi curve (see below) of the current MERS cases from Riyadh suggests that the outbreak is being contained. The graph compares a 4-day moving average of the number of daily cases reported from Riyadh by the Saudi Arabia Ministry of Health with the 4-day moving average of the distribution of onset dates (posted by WHO) for the reported cases. Because onset dates are not reported by the Saudi Arabia Ministry of health there is a time lag between the initial posting of the cases, and the reporting of onset dates. The declining trend in the number of cases being reported from Riyadh by the Saudi Arabia Ministry of Health suggests this outbreak is being contained and may be over shortly. 

Friday, July 31, 2015

Correlating the World Health Organization (WHO) Line List of MERS Case Numbers from the Republic of Korea (ROK)

The recent outbreak of Middle East Respiratory Syndrome (MERS) in the Republic of Korea (ROK) is the largest outbreak outside of the Arabian Peninsula since MERS was first reported in 2012. A total of 185 cases of MERS have been reported to date by the World Health Organization (WHO) from the ROK (see Annex 1). The media has reported that the outbreak in the ROK is over (link), however, WHO does not consider an infectious disease outbreak to be over until twice the maximum incubation period has passed interrupting the chain of human-to-human transmission. The maximum incubation period for MERS is believed to be14 days. The end of the outbreak will only be signaled 28 days after the last MERS-infected individual in the ROK tests negative sometime in the future.

Because of the size and nature of the MERS outbreak in the ROK, researchers will be analyzing the epidemiological data from the ROK outbreak in the future to assess what can be learned from this outbreak. Critical to such analysis is accurate, individual details of each case.

Below is a table correlating the WHO line list of MERS case numbers from the ROK (see Annex 1) with the line list of case numbers from the ROK Ministry of Health and Welfare (see Annex 2), and the line list of MERS disease events from ROK reported by Food and Agriculture Organization of the United Nations (FAO) (link).

A link to a pdf file of this table and  a CSV table of this data are presented below. Hopefully this concordance table will be useful to current and future MERS researchers.

General Table Comments:

1. There are some discrepancies in patient ages between the WHO line list of cases and the ROK line list of cases.

2. ROK Ministry of Health case #10 is not included in the WHO line list from the ROK. This case was reported from China on May 30, 2015 (link) with symptom onset of May 21, 2015 (WHO MERS ordinal number: 1148). While this case is considered part of the 2015 Asia outbreak of MERS it is not included in the WHO line list of cases from the ROK.

3. WHO ordinal case numbers are not necessarily in the correct order for individual cases when WHO presents aggregate case counts in a Disease Outbreak News reports.

4. There appears to be some discrepancies between FAO MERS case data and WHO MERS case data.  

5. The correlation presented in the above table is the best informed concordance of case listings.

Details of Column Headings:

WHO Case Number: WHO Case Number for MERS cases from ROK

Ordinal Case Number, WHO: Ordinal MERS Case Number based on WHO Disease Outbreak News reports

ROK Case Number: ROK Ministry of Health and Welfare Case Number

WHO Age: Age reported by WHO

ROK Age: Age reported by ROK Ministry of Health

WHO Gender: Gender reported by WHO

ROK Gender: Gender reported by ROK Ministry of Health

Onset Date: Symptom onset date reported by WHO

FAOid: Disease event identifier from FAO for ROK MERS cases

Caseid: Unique case identifier number

Annex 2. MERS Case Details reported by ROK Ministry of Health and Welfare

ROK Case Number 1 to 145 (June 14, 2015)

ROK Case Number 146 to 150 (June 15, 2015)

ROK Case Number 151 to 154 (June 16, 2015)

ROK Case Number 155 to 162 (June 17, 2015)

ROK Case Number 163 to 165 (June 18, 2015)

ROK Case Number 166 (June 19, 2015)

ROK Case Number 167 to 169 (June 21, 2015)

ROK Case Number 170 to 172 (June 22, 2015)

ROK Case Number 173 to 175 (June 23, 2015)

ROK Case Number 76 to 179 (June 24, 2015)

ROK Case Number 180 (June 25, 2015)

ROK Case Number 181 (June 26, 2015)

ROK Case Number 182 (June 27, 2015)

ROK Case Number 183 (July 2, 2015)

ROK Case Number 184 (July 3, 2015)

ROK Case Number 185 (July 4, 2015)

ROK Case Number 186 (July 5, 2015)


Monday, June 15, 2015

Where are the pediatric cases of MERS Infections?

Prior to the report of the Middle East Respiratory Syndrome (MERS) outbreak in the Republic of Korea (South Korea) in mid-May, more than 1000 cases of MERS had been reported from around the world since 2012. Most of these cases, about 87%, have been reported from the Kingdom of Saudi Arabia (Saudi Arabia). Only about 3% of the MERS cases reported through mid-May from Saudi Arabia can be can be classified as pediatric cases (cases less than 18 years old). There has been speculation that Saudi Arabia has had pediatric cases of MERS that were unreported (link).

Through June 14, 2015, South Korea has reported 150 MERS cases. The number MERS cases reported from South Korea is second only to Saudi Arabia. Since the beginning of the outbreak in South Korea only a single pediatric MERS case has been reported, a hospitalized, 16-year-old male.

As unfortunate as the outbreak in South Korea is, it provides an important data set for analyzing the nature of MERS infections. The South Korea outbreak was caused by a single individual (index case) who was infected on the Arabian Peninsula and returned to South Korea. Unlike the Arabian Peninsula, there is no evidence that any animal species on the Korean Peninsula is infected with or could transmit the MERS coronavirus to humans. The infection of all 150 cases in South Korea is a direct result of human-to-human transmission that can be traced back to the initial index case.

A risk assessment from the European Centre for Disease Prevention and Control (ECDC) (link) provides a graph showing the relationship of age groups of MERS cases distinguished by gender for about 200 cases from Saudi Arabia since the beginning of 2015 and the 107 cases from South Korea since the MERS outbreak began. The graphs seem to show a comparable age distribution of infected individuals from South Korea and Saudi Arabia in 2015. A more rigorous statistical comparison can be developed by comparing the age distribution of the currently confirmed 150 cases from South Korea with the most recent 150 MERS cases reported by the Saudi Arabia Ministry of Health (150 cases since February 15, 2015).

The table and graph below present the count and percentages of MERS cases by10-year age groups for these two countries. The table and graph demonstrate that there is a high correspondence in MERS cases by age category between South Korea and Saudi Arabia. In fact, these two age-category distributions of infected individuals, separated geographically by almost 7500 km, are highly correlated with an R value of .95. But, what can we learn from this table and what does this correlation tell us?

First, it tells us that pediatric cases are rare in South Korea, and by extension, they are also rare in Saudi Arabia. Second, the high correlation coefficient, along with few pediatric cases in both countries, indicates that Saudi Arabia is not hiding or covering up pediatric cases of MERS. Third, its tells us that MERS seems to be differentially infecting adults compared to children or adolescents. Why this is the case is not clear.

It is important to reiterate that all of the MERS cases in  South Korea are a result of human-to-human transmission. None of the MERS cases in South Korea are a result of the coronavirus jumping from an animal host to humans. The outbreak in South Korea is shedding light on the nature of the MERS coronavirus and how it affects and transmits among humans.