Risk factors for transmission of Middle East respiratory syndrome coronavirus infection during the 2015 outbreak in South Korea

Abstract

Background. Transmission heterogeneity was observed during the 2015 Korean outbreak of Middle East respiratory syndrome coronavirus (MERS-CoV) infection. Only 22 of 186 cases transmitted the infection, and 5 super-spreading events caused 150 transmissions. We investigated the risk factors for MERS-CoV transmission. Methods. Epidemiological reports were used to classify patients as nonspreaders, spreaders, or those associated with a super-spreading event (5 or more transmissions). Logistic regression analyses were used to evaluate the factors for MERS-CoV transmission. Results. Compared to nonspreaders, spreaders exhibited a longer interval from symptom onset to isolation (7 days vs 3 days) and more frequent pre-isolation pneumonia diagnoses (68.2% vs 17.1%). Spreaders also exhibited higher values for pre-isolation contacts (149 vs 17.5), pre-isolation hospitalization (68.2% vs 16.5%), and emergency room (ER) visits (50% vs 7.3%). Spreaders exhibited lower cycle thresholds for the upE and ORF1a genes (22.7 vs 27.2 and 23.7 vs 27.9, respectively). In multivariate analysis, transmission was independently associated with the cycle threshold (odds ratio [OR], 0.84; 95% confidence interval [CI], 0.75-0.96) and pre-isolation hospitalization or ER visits (OR, 6.82; 95% CI, 2.06-22.84). The super-spreading events exhibited higher values for pre-isolation contacts (777 vs 78), pre-isolation ER visits (100% vs 35.3%), and doctor shopping (100% vs 47.1%) compared to non-super-spreading events. Conclusions. These findings indicate that transmission is determined by host infectivity and the number of contacts, whereas super-spreading events were determined by the number of contacts and hospital visits. These relationships highlight the importance of rapidly enforcing infection control measures to prevent outbreaks.