Secondary attack rate of COVID-19 in non-household contacts - A systematic review of global studies

Abstract

Objective: Secondary Attack Rate (SAR) of COVID-19 varies across various populations. We aim to assess global articles reporting SAR in non-household contacts of COVID-19 patients through systematic review approach. Methods: Four databases - MEDLINE, SCOPUS, Google Scholar and EMBASE were systematically searched for retrieval of articles reporting SAR of COVID-19 in various contacts. Initial search provided 436 articles, which through series of evaluation finally yielded 14 articles. Result: Findings suggested that SAR in various contacts varies widely. Substantial number of studies (50%) were from China; however, the two largest studies were from India. Irrespective of type of contacts, overall SAR ranged from 0.55-6%. Highest risk was found from non-household close (family, friends) contacts (2.2-22.31%) followed by casual contact (travel, meal and health-care contacts). In spite of prolonged contact with the patients, SAR was lowest in health-care workers (0-7.3%). Review highlighted that the included studies were suffering from limitations of missing data and continuously evolving operational guidelines. Conclusion: The review showed that studies furnishing SAR data in non-household contacts are limited in number and exact mode of transmission is yet not clear. Six-percent of overall SAR indicates that though the disease is infectious in nature and proper precautions must be taken, not everybody that comes in contact with the index case is infected. However, with greater risk in non-household close contacts, it is important to identify vulnerable population and implement effective preventive strategies in them. Review also indicated serious data gaps in the published literature and stipulated need of more global studies.