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RESEARCH Analysis of SARS-CoV-2 Transmission in Different Settings, Brunei Liling Chaw, Wee Chian Koh, Sirajul Adli Jamaludin, Lin Naing, Mohammad Fathi Alikhan, Justin Wong We report the transmission dynamics of severe acute re- of SSEs are contingent on the environmental, behav- spiratory syndrome coronavirus 2 (SARS-CoV-2) across ioral, and host factors that drive transmission and the different settings in Brunei. An initial cluster of SARS- most effective interventions to control those factors. CoV-2 cases arose from 19 persons who had attended To address these factors, we report an analysis of a the Tablighi Jama’at gathering in Malaysia, resulting in transmission chain in Brunei that resulted from an in- 52 locally transmitted cases. The highest nonprimary at- ternational SSE. tack rates (14.8%) were observed from a subsequent Brunei is a small, well-connected country in religious gathering in Brunei and in households of at- Southeast Asia with a population of 459,500 (5). tendees (10.6%). Household attack rates from symptom- Brunei has multiple land borders and limited state atic case-patients were higher (14.4%) than from asymp- capacity to manage large-scale outbreaks (6). Multi- tomatic (4.4%) or presymptomatic (6.1%) case-patients. generation households are common and social in- Workplace and social settings had attack rates of <1%. Our analyses highlight that transmission of SARS-CoV-2 teractions center on strong family and religious re- varies depending on environmental, behavioral, and host lationships (7,8). These characteristics make Brunei factors. We identify red flags for potential superspreading particularly vulnerable to outbreaks and the rapid events, specifically densely populated gatherings with pro- progression of clusters to widespread community longed exposure in enclosed settings, persons with recent transmission (9). travel history to areas with active SARS-CoV-2 infections, A COVID-19 case was detected in Brunei on and group behaviors. We propose differentiated testing March 9, after a 4-day religious gathering, Tablighi strategies to account for differing transmission risk. Jama’at, in neighboring Kuala Lumpur, Malaysia. The Tablighi Jama’at gathering in Malaysia has been ases of coronavirus disease (COVID-19) have es- recognized as an SSE and had >16,000 attendees, in- Ccalated since the disease was initially reported on cluding international participants (10). Tablighi is December 31, 2019. A rapid response by the global an apolitical Islamic movement with adherents from scientific community has described many aspects >200 countries. Tablighi adherents usually gather of the causative agent, severe acute respiratory syn- at annual international events lasting several days drome coronavirus 2 (SARS-CoV-2). Estimates sug- where they participate in communal prayers, meals, gest a basic reproduction number of 2–3 in the early and speeches. In Malaysia, the participants stayed stages of the outbreak (1), which can be valuable in and slept at the mosque, and several of them were assessing the spread of the virus but obscures indi- deputized to cook and clean. Seventy-five persons vidual heterogeneity in the level of infectivity among from Brunei attended this event. Of the 135 con- persons and in different settings (2,3). Early reports firmed cases in Brunei reported by the first week of suggest that superspreading events (SSEs) might play April, 71 (52.6%) cases had an epidemiologic link to a role in the explosive propagation of SARS-CoV-2 this event (Figure 1). (4). Targeted approaches that reduce the likelihood Because SARS-CoV-2 is a novel infection in a na- ive population, an outbreak investigation of this event Author affiliations: Universiti Brunei Darussalam, Jalan Tungku can provide insights into its transmission dynamics Link, Brunei (L. Chaw, L. Naing); Centre for Strategic and Policy and the effectiveness of outbreak control measures. Studies, Jalan Pasar Baru Gadong, Brunei (W.C. Koh); Ministry Brunei’s thorough contact tracing provides a rare op- of Health, Bandar Seri Begawan, Brunei (S.A. Jamaludin, portunity to study the epidemiologic and transmis- M.F. Alikhan, J. Wong) sion characteristics of SARS-CoV-2 in different com- DOI: https://doi.org/10.3201/eid2611.202263 munity settings. 2598 Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 26, No. 11, November 2020 SARS-CoV-2 Transmission in Different Settings Figure 1. Epidemic curve for the first 135 cases of coronavirus disease (COVID-19) in Brunei Darussalam by cluster groups. Tablighi Jama’at cases were related to a religious gathering in Kuala Lumpur, Malaysia, during February 28–March 1, 2020. Methods a fever and cough and having recently traveled to Kuala Lumpur. Surveillance and Case Identification Brunei’s Ministry of Health (MoH) is responsible for Epidemiologic Investigation communicable disease surveillance and implemented Under the Infectious Disease Act, MoH conducted testing criteria for suspected COVID-19 cases on Jan- epidemiologic investigations and collected data for uary 23, 2020. Initially, only persons with acute respi- each case and close contact by using the World Health ratory symptoms and history of travel to a high-risk Organization’s first few cases protocol (12). The first area were tested for SARS-CoV-2. Over the next sev- identified case-patient was interviewed for demo- eral weeks, the program expanded to include contacts graphic characteristics, clinical symptoms, travel of a confirmed case, regardless of symptoms; persons history, activity mapping, and contact history. Once with pneumonia admitted to an inpatient healthcare MoH identified the case-patient’s participation at the facility; and persons with acute respiratory illness Tablighi event in Malaysia, they identified several treated at a health facility for the second time within other persons from Brunei who also had participated 14 days. On March 21, MoH started testing and isolat- at the event. We subsequently obtained the details of ing all travelers and returning residents. On March all participants from Brunei. 25, MoH introduced SARS-CoV-2 sampling at select- NP swabs were collected from all identified ed sentinel health centers to test persons with influen- participants and tested with RT-PCR. Persons who za-like symptoms, and on April 7, MoH implemented tested positive were admitted to the National Iso- mandatory random screening for selected groups of lation Centre (NIC). Persons who tested negative foreign workers. were quarantined for 14 days after their return to MoH defined a confirmed COVID-19 case as a Brunei at a designated community quarantine facil- person who tested positive for SARS-CoV-2 through ity, where they were screened for symptoms and real-time reverse transcription PCR (RT-PCR) testing body temperature daily. Persons who had symp- on a nasopharyngeal (NP) swab specimen (11). The toms develop at the NIC were retested. Activity first positive case in Brunei was detected on March mapping of confirmed cases was conducted, and 9 in a person who met the testing criteria by having contact tracing was initiated. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 26, No. 11, November 2020 2599 RESEARCH We defined a close contact as any person living relationships or housekeepers living in the household). in the same household as a confirmed case-patient We defined relatives as persons related to a case-pa- or someone who had been within 1 m of a confirmed tient who lived outside the household, workplace con- case-patient in an enclosed space for >15 minutes tacts as persons encountered at a workplace or school, (13). We identified secondary cases through inter- and social contacts as those encountered during travel views and checked cellular phone data when infor- or at social events. We defined contacts from a local mation on contacts was uncertain. NP swabs from all religious gathering as persons who attended a local close contacts of confirmed case-patients were tested Tablighi event in Brunei on March 5; the event ran by using RT-PCR. Persons who tested positive were throughout the night, and participants stayed all night. admitted to the NIC and persons who tested negative Such small local weekly gatherings usually take place were placed under home quarantine for 14 days from among Tablighi adherents in their home countries. their last exposure to the confirmed case-patient. Public health workers monitored the compliance and Data Analysis health status of persons under home quarantine daily We used χ2, Fisher exact, or Mann-Whitney tests to through video calls or face-to-face assessments. Per- compare groups of primary and nonprimary cases, sons who had symptoms develop during home quar- as appropriate. We calculated the incubation period antine were retested. from dates of exposure and symptom onset, when these were clear. We calculated serial interval by Clinical Management subtracting the date of symptom onset of an infectee All confirmed case-patients were treated and isolat- (secondary case) from the date of symptom onset of ed at the NIC and monitored until recovery. We ob- the infector (primary case); we only included symp- tained clinical information on case histories, includ- tomatic and presymptomatic infector–infectee pairs ing any prior treatment by health services, clinical for which epidemiologic links were clear. examination, and laboratory and radiological results, We calculated the attack rate for each setting by from digital inpatient records on the national health dividing the number of positive contacts by the to- information system database. In addition, we collect- tal number of close contacts. To identify risk factors ed information on each case-patient’s oral history to for infection, we applied a log-binomial regression ascertain whether they had symptoms ≤14 days be- analysis to estimate the risk ratio for gender, age, and fore diagnosis. Case-patients were discharged from setting. We performed further stratification to assess the NIC after 2 consecutive negative specimens col- differences in the symptom status of infectors across lected ≥24 hours apart.