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MERS less fatal in South Korea than in Saudi Arabia, analysis reveals

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Fatality rate among South Korean MERS cases is half that seen in Saudi Arabia

BOSTON (August 19, 2015) – Fewer patients in the South Korean outbreak of Middle Eastern respiratory syndrome (MERS) coronavirus have succumbed to the virus than expected when compared to Saudi Arabia, where the virus originated, according to epidemiologists from Boston Children's Hospital. As of July 15, 2015, 22 percent of recorded MERS cases in South Korea had died from the virus, fully one-half the case fatality rate (CFR) seen thus far in Saudi Arabia (44 percent).

These findings—reported by Boston Children's Maimuna Majumder, MPH, John Brownstein, PhD, and colleagues in the journal Emerging Infectious Diseases—arose from a preliminary analysis of mortality risk factors associated with the South Korean outbreak, the largest MERS outbreak outside of Saudi Arabia to date.

Using MERS case data reported by the World Health Organization and the South Korean Ministry of Health and Welfare, Majumder and Brownstein's team evaluated associations between MERS mortality and five risk factors:

  • sex
  • age
  • concurrent condition status (did the patient have pre-existing health problems?)
  • heath care worker status (was the patient a health care worker?)
  • the length of time from onset of symptoms to diagnosis

Of the 159 South Korean MERS cases for which outcomes and complete patient histories were available in the data (out of 186 total cases), 35 were fatal, yielding a case fatality rate of 22 percent. In contrast, 462 of the 1,049 patients reported by the Saudi Arabia Ministry of Health as of July 21, 2015 had died of the virus.

Only two of the five factors the research team analyzed—age and pre-existing health problems—were significantly associated with mortality risk in the South Korean outbreak, similar to data reported elsewhere for cases in Saudi Arabia.

Researchers caution that fatality calculations may change over time

"Some of the cases included in our South Korean data were still hospitalized when we ran our analyses," says Majumder, a computational epidemiology fellow in Brownstein's group and an engineering systems doctoral student at the Massachusetts Institute of Technology. "The final CFR for the South Korean outbreak may be a bit higher in the long run, but will likely still be significantly lower than what we’ve seen in Saudi Arabia."

Why mortality rates seen in South Korea and Saudi Arabia differ so greatly is not yet clear, though the authors did note that the rate of pre-existing conditions among MERS patients in in South Korea (16 percent) was far lower than in Saudi Arabia (96 percent). Additional analyses may yet reveal further possible reasons for the disparity, as well as associations with other risk factors.

"There may be differences in risk factor prevalence, treatment approach, or surveillance between the two countries," explains Brownstein, who is Boston Children's chief innovation officer, director the Computational Epidemiology Group in the hospital's Computational Health Informatics Program and co-founder of HealthMap. "This is not the final word on MERS in South Korea."

The study was supported by the National Library of Medicine (grant number R01LM010812).

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