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.

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