COVID-19 Without Symptoms in a King County, Washington, Nursing Home, March 2020

Summary

• Once SARS-CoV-2 gets into a long-term care skilled nursing facility (SNF), it can spread fast.
• After a health care worker there tested positive, 76 of 82 residents of an SNF were tested; 23 (30.3%) were positive, and about half had no symptoms that day.
• Symptom-based screening may miss many infections, and residents without symptoms may still spread the virus. Once a facility has a confirmed case, all residents should be cared for with CDC-recommended personal protective equipment (PPE), extending or reusing it where needed.

What happened

Older adults are vulnerable to severe COVID-19 because of age and, often, other conditions. An outbreak at one King County SNF, found on February 28, 2020, had already shown how fast the virus can move in such places.

• On March 1, a health care provider at a second King County SNF ("facility A") tested positive, having worked while sick on February 26 and 28.
• The facility immediately restricted visitors, checked residents for symptoms twice a day, and screened staff for fever each shift.
• By March 6, seven residents had symptoms and tested positive. Public Health – Seattle & King County and CDC recommended isolating all residents with symptoms and full protection — gowns, gloves, eye protection, facemasks and hand hygiene — for staff entering their rooms.
• On March 13, CDC assessed symptoms and tested 76 (92.7%) of the 82 residents (three refused, two with symptoms had been hospitalized, one was unavailable).

How symptoms were judged

Nursing staff reviewed each resident's screening records for the previous 14 days, and clinicians interviewed residents at testing (for residents with significant cognitive impairment, records only). Typical symptoms were fever, cough and shortness of breath; atypical ones included sore throat, chills, increased confusion, runny or stuffy nose, muscle aches, dizziness, malaise, headache, nausea and diarrhea. A resident was symptomatic with any new or worsened symptom, and asymptomatic with none (or only long-standing, unchanged ones). Positive residents without symptoms were checked again a week later; those who had fallen ill were counted as presymptomatic.

The state public health lab ran RT-PCR tests; the cycle threshold (Ct) — the cycle at which virus is detected — is lower when there is more viral RNA, and under 40 counts as positive.

What was found

• 23 of 76 (30.3%) residents were positive, with demographics similar to those testing negative.
• Of the 23, 10 (43.5%) had symptoms — eight typical, two only atypical (most often malaise and nausea) — and 13 (56.5%) had none.
• A week later, 10 of those 13 had developed symptoms — mainly fever (8), malaise (6) and cough (5), on average 3 days after testing. Only three stayed symptom-free.
• Ct values were low — meaning lots of virus — across every group: 18.6–29.2 with typical symptoms, 24.3–26.3 with atypical only, 15.3–37.9 presymptomatic and 21.9–31.0 asymptomatic, with no significant difference between groups.
• 13 (24.5%) residents who tested negative had also had typical or atypical symptoms in the previous two weeks.

Cycle threshold values by symptom status among residents who tested positive. Figure from the CDC report.

What it means

Sixteen days after the virus arrived, 30.3% of residents were infected despite early infection control — very rapid spread. About half of infected residents had no symptoms when tested, so residents who weren't recognized or isolated may have spread it further — much as influenza in older people often shows few or unusual symptoms. Their low Ct values, similar to those of asymptomatic people in China known to have transmitted the virus, show the potential for heavy shedding; studies of whether the virus was live were under way.

Why nursing homes are hard: residents may share rooms; care means close, prolonged contact; staff may have limited PPE experience; and recognizing symptoms and isolating people is especially hard with dementia — while symptoms like these have many other causes in this population. Here the virus came in with a health care provider, which may have sped its spread.

Limits: judging symptoms in people with cognitive impairment is hard (though typical of nursing homes), and the findings may not apply to younger or healthier people.

What facilities should do

• Keep the virus out: restrict visitors (except compassionate care) and nonessential staff; have staff watch for fever and symptoms and screen everyone at the start of each shift; and support sick leave, even for mild illness.
• Once there is a case: limit contact between residents; have all staff wear facemasks; and if possible use full CDC-recommended PPE — gown, gloves, eye protection and an N95 respirator (or a facemask if none) — for all residents, extending or reusing PPE where supplies are short.
• As testing improves: consider testing everyone to group infected residents together, in a dedicated unit or a separate COVID-19 facility.

Sources

Based on Anne Kimball, Kelly M. Hatfield, Melissa Arons and others, with Public Health – Seattle & King County and the CDC COVID-19 Investigation Team, "Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility — King County, Washington, March 2020," MMWR, Centers for Disease Control and Prevention (Early Release, March 27, 2020); a work of the United States government in the public domain.