Wednesday, May 13, 2020

MMWR Early Release: COVID-19 Superspreading Event In A Church Choir


Although many states are looking to roll back their lockdowns and reopen their economies, the CDC's MMWR published an early release yesterday which provides a cautionary tale on just how easily a single symptomatic carrier of the virus can infect a large number of people in the right setting.

High SARS-CoV-2 Attack Rate Following Exposure at a Choir Practice — Skagit County, Washington, March 2020

Early Release / May 12, 2020 / 69

Lea Hamner, MPH1; Polly Dubbel, MPH1; Ian Capron1; Andy Ross, MPH1; Amber Jordan, MPH1; Jaxon Lee, MPH1; Joanne Lynn1; Amelia Ball1; Simranjit Narwal, MSc1; Sam Russell1; Dale Patrick1; Howard Leibrand, MD1 
What is already known about this topic?
Superspreading events involving SARS-CoV-2, the virus that causes COVID-19, have been reported.
What is added by this report?
Following a 2.5-hour choir practice attended by 61 persons, including a symptomatic index patient, 32 confirmed and 20 probable secondary COVID-19 cases occurred (attack rate = 53.3% to 86.7%); three patients were hospitalized, and two died. Transmission was likely facilitated by close proximity (within 6 feet) during practice and augmented by the act of singing.
What are the implications for public health practice?
The potential for superspreader events underscores the importance of physical distancing, including avoiding gathering in large groups, to control spread of COVID-19. Enhancing community awareness can encourage symptomatic persons and contacts of ill persons to isolate or self-quarantine to prevent ongoing transmission.

On March 17, 2020, a member of a Skagit County, Washington, choir informed Skagit County Public Health (SCPH) that several members of the 122-member choir had become ill. Three persons, two from Skagit County and one from another area, had test results positive for SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19).
Another 25 persons had compatible symptoms. SCPH obtained the choir’s member list and began an investigation on March 18. Among 61 persons who attended a March 10 choir practice at which one person was known to be symptomatic, 53 cases were identified, including 33 confirmed and 20 probable cases (secondary attack rates of 53.3% among confirmed cases and 86.7% among all cases). Three of the 53 persons who became ill were hospitalized (5.7%), and two died (3.7%).
The 2.5-hour singing practice provided several opportunities for droplet and fomite transmission, including members sitting close to one another, sharing snacks, and stacking chairs at the end of the practice. The act of singing, itself, might have contributed to transmission through emission of aerosols, which is affected by loudness of vocalization (1). Certain persons, known as superemitters, who release more aerosol particles during speech than do their peers, might have contributed to this and previously reported COVID-19 superspreading events (2–5).
These data demonstrate the high transmissibility of SARS-CoV-2 and the possibility of superemitters contributing to broad transmission in certain unique activities and circumstances.
It is recommended that persons avoid face-to-face contact with others, not gather in groups, avoid crowded places, maintain physical distancing of at least 6 feet to reduce transmission, and wear cloth face coverings in public settings where other social distancing measures are difficult to maintain.
         (Continue . . . )

This isn't the first time we've seen church going, and singing, linked to the spread of COVID-19.  In April 10th's MMWR  Presymptomatic Transmission of SARS-CoV-2 — Singapore, January 23–March 16, 2020researchers identified 7 clusters of cases in which presymptomatic transmission is the most likely explanation for the occurrence of secondary cases.

Among them:
Cluster F. A woman aged 58 years (patient F1) attended a singing class on February 27, where she was exposed to a patient with confirmed COVID-19. She attended a church service on March 1, where she likely infected a woman aged 26 years (patient F2) and a man aged 29 years (patient F3), both of whom sat one row behind her. Patient F1 developed symptoms on March 3, and patients F2 and F3 developed symptoms on March 3 and March 5, respectively.
Singapore's Ministry of Health has also reported several other church-related clusters.
It is worth noting that South Korea's huge February surge in COVID-19 cases was also caused - in large part - by the transmission of the virus among thousands of members of the Shinchon Daegu Church.  
A reminder that even as social distancing restrictions are relaxed, some types of gatherings are going to remain far riskier than others.