Asymptomatic Middle East Respiratory Syndrome coronavirus infection using a serologic survey in Korea

Abstract

Objectives: The rates of asymptomatic infection with Middle East Respiratory Syndrome (MERS) coronavirus vary. A serologic study was conducted to determine the asymptomatic MERS infection rate in healthcare workers and non-healthcare workers by exposure status.

Methods: Study participants were selected from contacts of MERS patients based on a priority system in 4 regions strongly affected by the 2015 MERS outbreak. A sero-epidemiological survey was performed in 1,610 contacts (average duration from exposure to test, 4.8 months), and the collected sera were tested using an enzyme-linked immunespecific assay (ELISA), immunofluorescence assay (IFA), and plaque reduction neutralization antibody test (PRNT). Among the 1,610 contacts, there were 7 ELISA-positive cases, of which 1 exhibited positive IFA and PRNT results.

Results: The asymptomatic infection rate was 0.060% (95% confidence interval, 0.002 to 0.346). The asymptomatic MERS case was a patient who had been hospitalized with patient zero on the same floor of the hospital at the same time. The case was quarantined at home for 2 weeks after discharge, and had underlying diseases, including hypertension, angina, and degenerative arthritis.

Conclusions: The asymptomatic infection was acquired via healthcare-associated transmission. Thus, it is necessary to extend serologic studies to include inpatient contacts who have no symptoms.

Keywords: Asymptomatic infection; Enzyme-linked immunespecific assay; Epidemiology; Middle East Respiratory Syndrome coronavirus; Nosocomial infections; Outbreak.

Figure 1.

Flowchart of participants in the Middle East Respiratory Syndrome (MERS) serologic survey in Korea. ¹ Major MERS outbreak areas including Seoul, Gyeonggi, Chungcheong, and Jeonbuk in Korea. ² Selection rates were different by characteristics of exposed MERS case and status of subjects (see the Table 1).