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. 2015 Oct:39:7-9.
doi: 10.1016/j.ijid.2015.08.005. Epub 2015 Aug 11.

Estimating the risk of Middle East respiratory syndrome (MERS) death during the course of the outbreak in the Republic of Korea, 2015

Kenji Mizumoto  1 , Masaya Saitoh  2 , Gerardo Chowell  3 , Yuichiro Miyamatsu  2 , Hiroshi Nishiura  4
Affiliations

Estimating the risk of Middle East respiratory syndrome (MERS) death during the course of the outbreak in the Republic of Korea, 2015

Kenji Mizumoto et al. Int J Infect Dis. 2015 Oct.

Abstract

Objectives: A large cluster of the Middle East respiratory syndrome (MERS) linked to healthcare setting occurred from May to July 2015 in the Republic of Korea. The present study aimed to estimate the case fatality ratio (CFR) by appropriately taking into account the time delay from illness onset to death. We then compare our estimate against previously published values of the CFR for MERS, i.e., 20% and 40%.

Methods: Dates of illness onset and death of the MERS outbreak in the Republic of Korea were extracted from secondary data sources. Using the known distribution of time from illness onset to death and an integral equation model, we estimated the delay-adjusted risk of MERS death for the South Korean cluster.

Results: Our most up-to-date estimate of CFR for the MERS outbreak in South Korea was estimated at 20.0% (95% confidence intervals (CI): 14.6, 26.2). During the course of the outbreak, estimate of the CFR in real time appeared to have decreased and become significantly lower than 40%.

Conclusions: The risk of MERS death in Korea was consistent with published CFR. The estimate decreased with time perhaps due to time-dependent increase in case ascertainment. Crude ratio of cumulative deaths to cases underestimates the actual risk of MERS death because of time delay from illness onset to death.

Keywords: Korea; MERS; case fatality ratio; epidemic; statistical estimation.

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Figures

Figure 1
Figure 1
Temporal distribution of cases and deaths due to Middle East respiratory syndrome coronavirus (MERS-CoV) in the Republic of Korea, 2015. Cumulative numbers of cases (A) and deaths (B) over time. As the dates of illness onset were not fully available from the midst of outbreak, we partially used dates of confirmatory diagnosis for a part of cases (white bars in panel A). Suspicious symptoms of contacts under observation have been closely monitored, and traced suspected cases have been consistently tested during the course of the outbreak.
Figure 2
Figure 2
The risk of death caused by Middle East respiratory syndrome coronavirus (MERS-CoV) in the Republic of Korea, 2015. Estimated case fatality ratio (CFR) as a function of calendar time. The two horizontal dashed grey lines represent published values of CFR, i.e., 20% and 40% [8,9]. The crude ratio is calculated as the ratio of cumulative numbers of deaths to cases, which likely underestimates the risk of death and may increase over the course of calendar time. The whiskers of estimated CFR extend to lower and upper 95% confidence intervals that were computed by the profile likelihood. B. Two-sided binominal test (p-value) as a function of time, comparing adjusted CFR against published values, 20% and 40%. The horizontal dashed grey line corresponds to the threshold value (5%).
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