A New Measure for Assessing the Public Health Response to a Middle East Respiratory Syndrome Coronavirus Outbreak

Cho, Sung-il

A traditional measure associated with an epidemic is the secondary attack rate (SAR), the proportion of secondary cases among those exposed, which is calculated by D/C, as shown in Figure 1 . The SAR reflects the transmission risk of the disease, assuming all contacts are identified. We propose a new measure, "timely quarantined proportion" (TQP), to represent the proportion of confirmed cases who have been monitored in a timely manner, that is, before symptom onset. This is a simple and straightforward measure that reflects the combined effects of public health responses, including early diagnosis, contact identification, and quarantine. TQP ranges between 0 to 1, and is calculated by M(TC)/D (Figure 1 ), using the data from the confirmed cases. It only takes into account information on whether a confirmed case has been identified before or after symptom onset. If the TQP approaches 1, it implies that most cases develop symptoms and become infective while already being monitored and, if appropriate, quarantined. No more contacts should be generated under effective quarantine, leading to an end of epidemic. If the TQP is low, e.g. 0.1, nine out of 10 confirmed cases have not been identi- The TQP can be used after an outbreak has ended to evaluate the responses to the outbreak. Perhaps an even more useful application is to monitor the ongoing responses during the epidemic. Any new confirmed case arising outside of the contact monitoring should trigger an alarm and an expansion in the range of the scope of monitoring sufficient to have included the missed case. An overall trend of an increase in the TQP would provide reassurance that the response is reasonably effective and the epidemic will end soon.