COVID-19: Presymptomatic Transmission in a Skilled Nursing Facility

COVID-19: Presymptomatic Transmission in a Skilled Nursing Facility.

Jefferson T,  Heneghan C. 1/01/2020.

https://www.cebm.net/study/covid-19-presymptomatic-transmission-in-a-skilled-nursing-facility/

Published on June 4, 2020

Reference Arons MM, Hatfield KM et al. Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility. New England Journal of Medicine. 2020;382(22):2081-90. 2020
Study type
Country USA
Setting Skilled Nursing Home
Funding Details None declared
Transmission mode Person to person
Exposures Nursing Home, Person to Person and HCW to person.

Bottom Line

On the basis of the reconstruction of an outbreak of COVID-19 in a skilled nursing facility, the presence of symptoms is not a sufficient indicator of infection. Viral shedding can continue for at least a week after testing positive.

Evidence Summary

This was a report of an investigation into an outbreak of COVID-19 in a skilled nursing facility in King County, Washington State, USA. The outbreak started on the 5th of March in an 89-resident facility and the investigation was concluded by the 3rd of April. Infected residents were classified as:

  • Symptomatic with typical symptoms (fever, cough, or shortness of breath) (21 residents)
  • Symptomatic with only atypical symptoms (4 residents)
  • Presymptomatic¬† (asymptomatic at the time of testing but developed symptoms within 7 days after testing).
  • Asymptomatic at time of testing (48 residents) of which 24 went on to develop symptoms within 4 days. Of these 15 are reported as having no symptoms and 12 as having symptoms either of long-standing diseases or non-worsening COVID-19 (e.g. cough).

What did they do?

The authors carried out an investigation and reconstruction of the outbreak. They tested the majority of residents on the 10th and again on the 17th of March for residents who had had either a negative test result or a positive result with atypical or no symptoms reported in the first survey (so-called point prevalence surveys).

On the day of testing nurses completed a standardized form for each resident tested, recording symptoms present in the preceding 14 days. Asymptomatics were reassessed one week later.  The surveys allowed the investigators to quantify and follow the evolution of the outbreak.

There were 89 residents in the facility, mostly elderly with pre-existing conditions (47/48). Of these 57 (64%) were positive for SARSCoV-2 either at the surveys or at post-mortem or during the point-prevalence surveys in the 23 days after the index case was identified (3-23 March). The demographic variables, co-mordibidites and symptoms were similar.

The authors report a doubling time of 3.4 days and remark that some cases shed virus for more than 7 days after symptom onset, implying the need for testing repeatedly before discharge or release from isolation. Alternatively, isolation time needs to be extended.

Study reliability

The authors discuss challenges in symptom ascertainment that may have resulted in misclassification for some residents. However, they used methods that are robust for the setting. It is not clear if these results generalize outside of this setting. Asymptomatic staff members were not tested, and the investigators we are unable to document their role in transmission.

Clearly defined setting Demographic characteristics described Follow-up length was sufficient Transmission outcomes assessed Main biases are taken into consideration
Yes Yes Yes Yes Unclear *
* Unclear = 76/89 residents took part in surveys. Healthcare workers were not assessed

What else should I consider?

The evidence from this report needs replicating, updating and incorporating into a systematic review with a predefined protocol and a clear search and inclusion strategy. Making inferences based on one study is prone to errors and the ecological fallacy. This evidence does not likely generalize outside of the nursing facility, ie. it does not apply to younger populations. Furthermore, there may be features of this population (i.e. more unwell) or the density of the population that means this evidence is not generalizable to other care facilities.

About the authors

Carl Heneghan

Carl Heneghan

Carl is Professor of EBM & Director of CEBM at the University of Oxford. He is also a GP and tweets @carlheneghan. He has an active interest in discovering the truth behind health research findings

Tom Jefferson

Tom Jefferson

Tom Jefferson is a senior associate tutor and honorary research fellow, Centre for Evidence-Based Medicine, University of Oxford.