Identifying and Interrupting Superspreading Events

Implications for Control of Severe Acute Respiratory Syndrome Coronavirus 2

Thomas R. Frieden; Christopher T. Lee


Emerging Infectious Diseases. 2020;26(6):1059-1066. 

In This Article

Prevention and Mitigation of SSEs

SSE prevention and mitigation depends, first and foremost, on quickly recognizing and understanding these events. This recognition and understanding enables implementation of control measures specific to the incident and identification of measures, which can reduce the risk for future SSEs. During the SARS epidemic, rapid quarantine and isolation reduced outbreak extent and speed,[19] and the lack of early detection was the primary cause of a hospital MERS outbreak in South Korea.[39] An analysis of available data from Hong Kong, Vietnam, Singapore, and Canada found that delaying SARS control measures by just a week could have tripled the size of the epidemic.[7] A modeling study of control interventions and SSEs in South Korea found that timely interventions (within 1 week), including a government announcement of affected hospitals, reduced the size and duration of MERS transmission.[28]

Healthcare facilities are critical for prevention and control of SSEs. Targeted control measures include rapid identification and isolation of all potentially infectious patients, including a high index of suspicion for transmissible diseases, and implementation of universal infection control procedures in all areas of all facilities.[20,40] Because individual superspreaders can only be identified retrospectively, universal implementation of triage procedures, rapid diagnosis and isolation, administrative controls (e.g., flow patterns and procedures for patients, visitors, and staff), and engineering controls (e.g., isolation rooms, partitions to protect against respiratory droplets, ventilation systems) are all necessary.[28] Meticulous infection control is especially needed when performing procedures such as bronchoscopy, intubation, suctioning, sputum induction, and nebulizer therapies, which can enable what would normally be a droplet-transmitted infection to become aerosolized and therefore able to be more widely disseminated. If these types of procedures are needed, they should be performed by using strict infection control procedures and, when possible, in airborne infection isolation units.

SSEs in healthcare settings can be associated with increased illness and death because many infections occur among patients with underlying conditions, which can delay diagnosis and exacerbate pathologic changes.[41,42] Most tuberculosis is spread by patients who have not yet been given a diagnosis, rather than by failure to effectively isolate these patients.[43] Risk factors for SSEs of SARS among 86 wards in Guangzhou, China, and 38 wards in Hong Kong were related to inadequate infection prevention and control, including insufficient availability of washing and changing facilities for staff, performing resuscitation on the ward, staff working while experiencing symptoms, and use of oxygen therapy or positive pressure ventilation.[25] One patient in China who had only abdominal symptoms was not initially suspected of having COVID-19 and was admitted to a surgical ward; >10 healthcare workers and ≥4 patients were presumed to have been infected by this patient.[3] It is essential that healthcare facilities implement infection control guidelines for COVID-19 rigorously. It is also essential that any nosocomial transmission is analyzed to identify the modes of spread, which will inform best strategies for prevention.

SSEs also occur in settings other than healthcare settings.[44] The SARS outbreak in Hong Kong was characterized by 2 SSEs responsible for >400 infections;[45] 1 guest at the Metropole Hotel was the index case for 4 national and international clusters.[46] Community-wide NPIs, including risk communication to the public on social distancing, hand and respiratory hygiene, and criteria for either self-isolation or safer presentation to the hospital, can limit community transmission. During the SARS outbreak, effective communication appears to have reduced time from symptom onset to hospital admission and decreased the number of persons with whom patients had contact before isolation.[25] The combination of facility-based and population-based interventions ended SARS transmission.[19,47]

A study modeling the impact of interventions in Wuhan found that, although early identification and isolation reduced the number of infections somewhat, integrated implementation of NPIs decreased the number of cases rapidly and substantially and drove the reproductive number to <1 (C. Wang et al., unpub. data, If NPIs had been implemented 2 weeks earlier, an estimated 86% of cases might have been prevented.[48] For COVID-19, broad infection prevention and control measures include cough and hand hygiene, self-isolation by staying home if sick, and avoiding infection during care-seeking and caregiving.