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. 2016 Apr 1;183(7):657-63.
doi: 10.1093/aje/kwv452. Epub 2016 Feb 4.

Estimating the Severity and Subclinical Burden of Middle East Respiratory Syndrome Coronavirus Infection in the Kingdom of Saudi Arabia

Justin Lessler, Henrik Salje, Maria D Van Kerkhove, Neil M Ferguson, Simon Cauchemez, Isabel Rodriquez-Barraquer, Rafat Hakeem, Thibaut Jombart, Ricardo Aguas, Ali Al-Barrak, Derek A T Cummings; MERS-CoV Scenario and Modeling Working Group
Collaborators

Estimating the Severity and Subclinical Burden of Middle East Respiratory Syndrome Coronavirus Infection in the Kingdom of Saudi Arabia

Justin Lessler et al. Am J Epidemiol. .

Abstract

Not all persons infected with Middle East respiratory syndrome coronavirus (MERS-CoV) develop severe symptoms, which likely leads to an underestimation of the number of people infected and an overestimation of the severity. To estimate the number of MERS-CoV infections that have occurred in the Kingdom of Saudi Arabia, we applied a statistical model to a line list describing 721 MERS-CoV infections detected between June 7, 2012, and July 25, 2014. We estimated that 1,528 (95% confidence interval (CI): 1,327, 1,883) MERS-CoV infections occurred in this interval, which is 2.1 (95% CI: 1.8, 2.6) times the number reported. The probability of developing symptoms ranged from 11% (95% CI: 4, 25) in persons under 10 years of age to 88% (95% CI: 72, 97) in those 70 years of age or older. An estimated 22% (95% CI: 18, 25) of those infected with MERS-CoV died. MERS-CoV is deadly, but this work shows that its clinical severity differs markedly between groups and that many cases likely go undiagnosed.

Keywords: MERS; burden; clinical symptoms; coronavirus; severity.

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Figures

Figure 1.
Figure 1.
Estimating the unseen iceberg. In order to estimate the number of undetected Middle East respiratory syndrome coronavirus infections, we assume that active surveillance detects cases irrespective of their place on the iceberg and that nearly all deaths are detected (denoted by the dashed box at right enclosing all parts of the iceberg). Passive surveillance, by contrast, detects cases above the waterline (box at left above the waterline) but not those below (box at left below the waterline). That is, deaths, severe symptoms, and mild/asymptomatic infections occur in the same proportion in those identified by active surveillance as they do in infections overall. We then use the proportion of persons with infections “above the waterline” (i.e., observed through passive surveillance) who die or develop symptoms severe enough to trigger Middle East respiratory syndrome coronavirus testing to infer the number of unseen infections.
Figure 2.
Figure 2.
Observed weekly incidence of Middle East respiratory syndrome coronavirus, June 24, 2012 to July 25, 2015, with survival status as of last report (light gray indicates living; dark gray indicates deceased). The dotted line indicates the smoothed naïve case fatality ratio over time.
Figure 3.
Figure 3.
Estimated symptomatic infection ratio (light gray) and infection fatality ratio (dark gray) of Middle East respiratory syndrome coronavirus infections in the Kingdom of Saudi Arabia, June 24, 2012 to July 25, 2015. Triangles indicate naïve case fatality ratios among identified cases.
See this image and copyright information in PMC

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