By Sharon Bogan

Public Health—Seattle & King County

The recent Delta-driven surge in COVID-19 cases affecting our region and nation is unfortunately not letting up. Over the last week, Public Health—Seattle & King County has reported an average of 318 new cases daily. That’s more than double the number of cases from just two weeks ago and nearly six times as many as a month ago.

Alongside this rise in cases are reports of outbreaks that often times involve more cases than earlier in the summer—before Delta was circulating as widely. Many of the outbreaks are occurring in indoor workplaces and social events among people who were not wearing masks and where ventilation was poor. Many outbreaks involve situations where both unvaccinated and vaccinated people are in indoor spaces together. We have not identified outbreaks yet where everyone is vaccinated.

Increase in outbreaks

Overall, in the last three weeks, Public Health has observed a large percentage of outbreaks reported in non-healthcare workplaces, including an office with 61 employees and 27 reported cases. Outbreaks are also occurring in facilities hosting large social events, such as a 100-person birthday party held at a country club with 25 reported cases.

Across all recent outbreaks, most cases occurred in people who were unmasked. Vaccinated individuals who tested positive reported mild symptoms. All hospitalized cases exposed at social events have been among unvaccinated individuals, with no deaths identified.

“Over the last several weeks, Public Health’s investigation and epidemiology teams have received a substantial number of reports of outbreaks,” said Meagan Kay, deputy chief for the Communicable Disease Epidemiology and Immunization Section of Public Health. “Large numbers of people are becoming infected when gathering together in indoor public settings and not wearing masks or taking other precautions to prevent COVID-19. This is concerning given the reports are likely just a subset of the total number of outbreaks taking place and exposing our community.”

A closer look at 3 outbreaks

A few patterns start to emerge from public health data when looking at three examples of recent outbreaks. Public Health appreciates the willingness of these three organizations to be forthcoming and help shed light on what our whole community can do to be safer.

• An indoor music club: In mid-July, Public Health conducted an outbreak investigation when several people with a positive COVID-19 test attended the same indoor event. A total of 26 cases have since been identified among 374 people attending the event. While the investigation is still ongoing, of the 26 cases,18 reported they were vaccinated. No hospitalizations or deaths have been reported with this outbreak.

Event organizers reported that the club required attendees to provide documentation of vaccination, but vaccination status was not verified for staff and some staff were not vaccinated. Masks were optional, and the event included singing. Because of the large number of attendees, distancing was not possible. Ventilation was compromised with some fans not working and challenges pulling fresh air into the space with no ability to open windows.

What this tells us: Outbreaks in crowded, poorly ventilated indoor spaces tell us that these spaces remain a risk. Even if vaccinated, Public Health recommends wearing a mask in indoor public settings to lessen the risk, unless a state-approved method is used to assure that all people allowed inside have been fully vaccinated. Even then, attendees might choose to wear a mask to reduce their risk of COVID-19 even further.

• An indoor fitness center: A fitness center held a charity workout event with approximately 70 people in attendance—about 35 people attending in two segments. A total of 16 cases have been identified to date, including 13 attendees, two staff, and one household member of an attendee. Fourteen of the 16 cases were verified to be fully vaccinated. All 16 cases developed symptoms of COVID-19, but none were hospitalized. Physical distancing was not maintained during workout sessions, and masks were optional.

Public Health visited the site to evaluate their indoor ventilation. While the site was deliberate in having large floor fans in the building, the Public Health team found that the facility’s ventilation system could be improved to allow for more adequate airflow.

What this tells us: Inadequate ventilation continues to come up as a factor in public health outbreak investigations.

The virus builds up in enclosed spaces as infected people breathe. And the risk increases when people are singing, shouting or exercising, with closer contact, no masking, and longer exposure.

Open windows and doors whenever possible to maximize the movement of air. Building and business owners should evaluate their HVAC systems to increase outside airflow, upgrade filtration where possible and consider the need for portable HEPA filtration. Resources are available on Public Health’s website and from CDC.

This outbreak also reinforces the importance of wearing masks in indoor public settings and maintaining physical distancing, regardless of vaccination status. Our outbreak data suggest that vaccinated people have been infected when in crowded indoor settings when not wearing masks.

The COVID-19 vaccines are incredibly effective, especially against serious illness, hospitalization, and death, and make it much less likely, but not impossible, that a person will catch and transmit COVID-19. With the more contagious Delta variant, when someone who is vaccinated gets infected, they could also potentially spread it to others. That is why wearing masks in indoor public settings is the best practice for everyone right now.

• A childcare program: In early July, Public Health was notified that two people tested positive for the virus at a childcare serving 135 students. Public Health worked with the center and determined that all the classrooms had exposed students or staff and recommended everyone test negative prior to returning to the center. As of the end of July, a total of 36 cases have been identified (19 students, three staff, and 14 household contacts). The childcare program requires everyone age 5 years and older, regardless of vaccination status, to wear masks; compliance with the policy was reportedly good. From the investigation, the outbreak appears to have started when three students who were too young to be required to wear masks attended childcare while symptomatic. The Public Health team found that 60% of staff were fully vaccinated. The team is working with the childcare to offer vaccination resources.

What this tells us: Staying home when ill and keeping children with any symptoms home is the best practice right now with the virus still circulating. This is essential in childcare settings where physical distancing is challenging to maintain, and masks are not worn by younger children. For parents and caregivers, this can be very difficult to keep kids home, particularly when kids have mild symptoms. But getting a COVID-19 test, which is a simple swab that does not go deep into the nose, and waiting for a negative result to return to work or childcare, are the best ways to prevent spread to others.

“We have high rates of COVID-19 in King County right now. The risk is highest for those who are unvaccinated, but this is a good time for everyone to remember that in addition to getting vaccinated, there are multiple ways to further reduce one’s risk, and layered protections are the best protections,” said Dr. Jeff Duchin, health officer for Public Health – Seattle & King County.

“The most important way to end this pandemic remains increasing vaccination coverage in our community. It saves lives, prevents illnesses, and reduces the spread of COVID-19. Given we still have so many people at risk, including children and those who are immunocompromised, remember that getting vaccinated is the single most important tool we have right now to protect individuals and our community. In addition, we have other simple and effective tools –masking, ventilation, staying home when ill, and physical distancing that can further reduce the risk for potentially serious COVID-19 infections.”

Vaccination, layered protection

There are approximately 370,000 King County residents who are eligible for vaccination and aren’t vaccinated who remain at risk for contracting the virus. Public Health urges all eligible people to get vaccinated as soon as possible to protect yourself and those around you.

In addition to vaccination, layered protection remains the best protection. That means using multiple strategies to reduce risk. We have great tools to fight COVID-19 – first among them are vaccines – but until we’re in a more stable and safer place, it’s important to remember there are other effective measures to further reduce our risk.

• Wearing a high quality, well-fitting mask indoors in public settings, regardless of vaccination status, provides an extra layer of protection for all of us

• Improving indoor air quality and ventilation

• Staying home when ill, isolating from others, and getting tested right away if exposed

• Maintaining physical distancing in crowded settings, especially indoors

• Limiting high-risk activities, including avoiding or limiting time spent in crowded indoor spaces