Investigation of COVID-19 clusters in Singapore

1. Three clusters of COVID-19 were identified that resulted in further transmission beyond household clusters, including a cluster that did not recently travel to China, suggesting a need for strong surveillance strategies to minimize spread of the virus.

Evidence Rating Level: 3 (Average)

Coronavirus disease 2019 (COVID-19) was first reported in Wuhan, China following the detection of a cluster of viral pneumonia cases. Singapore confirmed its first case of COVID-19 on January 23, 2020, with the number rising to 89 people by February 22, 2020, the first 18 of whom having reported recent trips to Wuhan. As COVID-19 has become a serious pandemic, this study analyzed three clusters of COVID-19, to assess interactions and potential modes of transmission. Clinical and epidemiological data was utilized, including medical records, interviews and field investigations. The study found that the three clusters involved a Chinese tour group, company conference, and a church rather than simply household clusters. A total of 36 cases of individuals tested positive for COVID-19, relating to Clusters A (11), B (20), and C (5), denoting the setting of transmission, respectively. Cluster A included individuals with interrelated interactions with the tour group. The only overlap in activities among those in Cluster C was that five of the patients visited the church at the same time. Estimated median incubation period was four days (IQR 3 to 6). While there could be further tertiary causes of transmission within the households – non-primary cause – the authors report that the serial interval for the three household transmission pairs was likely 3 to 8 days. Clinically, the most common symptoms were fever (88%) and cough (82%). This study noted a six-month-old male who was asymptomatic until a fever spike two days into hospitalization. Median time from symptom onset to hospital admission was four days (IQR 3 to 9). For most cases, the course was uncomplicated and resolved in the first few days. However, admissions were more protracted due to consistently positive findings of SARS-CoV-2 via nasopharyngeal swab testing. While no deaths were reported among these three clusters, close and prolonged exposure likely resulted in the COVID-19 cases, emphasizing the importance of hygiene in the prevention of transmission. While the first indication of human-to-human transmission was 11 days after the first case was noted, it is unlikely that temperature screening would have sufficiently detected concerns in travelers departing from Wuhan due to limited symptoms at the time. Therefore, this study and its authors suggest stronger surveillance to identify local cases even if they have not traveled to Wuhan or other international locations, as Cluster C is a prime example of individuals who presented with pneumonia but did not travel to China.

Click to read the study in Lancet

Image: PD

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