In a recent study posted to the medRxiv* pre-print server, researchers conducted a systematic review to evaluate the characteristics of super-spreaders of three novel coronaviruses (nCoV) that caused severe acute respiratory syndrome (SARS), Middle East Respiratory Syndrome (MERS), and coronavirus disease 2019 (COVID-19).
Most nCoV infected individuals transmit diseases to one or two individuals. However, some patients are ‘super spreaders’ – they are the primary source of several secondary infections. The identification of common factors among these super-spreaders would enable efficient containment and decrease the overall transmission of disease.
Although previous studies have reported on SARS and MERS super-spreaders, the super-spreading of COVID-19 is still taking place. Moreover, to date, the documentation of the characteristics of individual super-spreaders is limited.
About the study
In the present systematic review, researchers assessed studies reporting on the attributes of the MERS, COVID-19, and SARS super-spreaders to identify common factors among them. The index cases that transmitted infection to a minimum of nine people were considered as ‘super-spreaders’ for the present review.
Databases such as Scopus and MEDLINE were searched on June 3, 2020, and June 18, 2021, for studies on super-spreaders of MARS, COVID-19, and SARS infections. Additionally, pre-print servers such as bioRxiv and medRxiv and grey literature from credible sources or supported by public statements of the index cases themselves, interviews, or press releases were also included.
Studies were eligible for the systematic review if they were published between 2002 to mid-June 2021 in all languages, that could be translated to Spanish or English, of any study design and any study setting. These studies reported on MERS, SARS, or COVID-19 index cases diagnosed by reverse-transcription-polymerase chain reaction (rt-PCR), clinical manifestations, or cell culture with definite exposure history and transmitted infections primarily via the respiratory route face-to-face. Full-text articles selected by a minimum of two reviewers were included in the review and a third reviewer intervened in case of no consensus.
Data on sex, age, location, activities, ethnicity, occupation, transmission setting, symptom severity, medical conditions, and disease outcomes were obtained. The team recorded the count of first-generation cases and equated this to the count of secondary infections transmitted by the super-spreaders. The quality of all the studies was assessed and classified as ‘most credible’, ‘fairly credible’, or ‘poorly credible’ based on the number of ‘yes’ answers to the questions of the quality assessment checklist designed by the team.
A total of 14,905 studies from Scopus and MEDLINE and 400 pre-print articles were searched using Google scholar. Of these, 14,569 were excluded during the title and abstract screening whereas 336 were retained for the full-text review. After reviewing the entire text of articles, 260 were excluded and 87 new articles were included. As a result, data was extracted from 163 studies. From these studies, 14, 76, and 29 index cases of MERS, COVID-19, and SARS were identified, respectively.
The majority of the MERS-infected super-spreaders were South Korean men and transmitted infections in clinical settings - either hospitalized due to respiratory illness or attended clinics due to other reasons such as dialysis between 2014 and 2017. Their mean age was 48 years. Most of them had symptoms of severe illness, particularly pneumonia with 67% mortality. They transmitted infections to about two to 89 people.
SARS super-spreading mainly took place in the Far East (Hong Kong, Taiwan, or China) and Canada in clinical settings between December 2002 and April 2003. Most super-spreaders were men with a mean age of 54 years with symptomatic severe disease. They caused about four to 51 secondary infections.
Most of the COVID-19 super-spreaders were identified in the United States of America (USA) after May 31, 2020 (between June and August 2020) in the initial phase of the COVID-19 wave. In contrast to the SARS and MERS outbreaks, most COVID-19 super-spreading occurred in community settings. Additionally, most of the COVID-19-infected super-spreaders were either asymptomatic or had mild disease.
While most MERS or SARS super-spreaders were symptomatic and had in-hospital deaths, most COVID-19-infected super-spreaders had mild disease and died in community areas. Data on the occupation, activities, and ethnicity of all nCoV super-spreaders were largely unavailable. Additionally, the sex and age of COVID-19-infected super-spreaders were sparsely reported.
Overall, most super-spreaders were men aged above 40 years. Notably, most MERS and SARS super-spreaders were middle or old-aged symptomatic individuals with high in-hospital mortality whereas most COVID-19 super-spreaders were asymptomatic with mild disease irrespective of age and died in the community.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.