guidelines for stopping home isolation, for health care workers; stability of SARS-CoV-2 in aerosol and surfaces

The CDC just released their guidelines for when home isolation can be discontinued for non-hospitalized  people with COVID-19 (see https://www.cdc.gov/coronavirus/2019-ncov/hcp/disposition-in-home-patients.html )

For those who have not been tested for the virus:

-- discontinuation of home isolation for those who have symptoms:

    -- at least 3 days (72 hours) have passed since recovery, defined as resolution of fever without the use of fever-reducing medicines and improvement in respiratory symptoms (e.g. cough, shortness of breath)

    -- and, at least 7 days have passed since symptoms first appeared

For those who have tested positive for the COVID-19 virus (laboratory confirmation):

-- discontinuation of home isolation for those have symptoms, when:

    -- resolution of fever without the use of fever-reducing medications

    -- and, improvement in respiratory symptoms (e.g. cough, shortness of breath)

    -- and, negative results of 2 consecutive nasopharyngeal swab specimens collected at least 24 hours apart

-- for asymptomatic individuals who have tested positive for the virus:

    -- discontinue home isolation when at least 7 days have passed since the date of the first positive diagnostic test, and there has been no subsequent illness

 

---------------------------------------

Return to work criteria for health care personnel (see https://www.cdc.gov/coronavirus/2019-ncov/healthcare-facilities/hcp-return-work.html )

For those with confirmed infection with COVID-19:

-- exclude from work until:

    -- resolution of fever without the use of fever-reducing medications

    -- and, improvement in respiratory symptoms (e.g. cough, shortness of breath)

    -- and, negative results of the COVID-19 assay from at least 2 consecutive nasopharyngeal swab specimens collected at least 24 hours apart

for those not tested for COVID-19:

--exclude from work until:

    -- at least 3 days (72 hours) have passed since recovery, defined as resolution of fever without the use of fever-reducing medications and improvement in respiratory symptoms (e.g. cough, shortness of breath)

    -- and, at least 7 days have passed since symptoms first appeared

-- after returning to work

    -- healthcare workers should wear a facemask at all times in the facility until all symptoms have completely resolved or until 14 days after the illness onset, whichever is longer

    -- they should not be in contact with severely immunocompromised patients until 14 days after illness onset

    -- adhere to hand hygiene, respiratory hygiene, and cough etiquette (e.g. cover nose and mouth when coughing or sneezing, dispose of tissues in waste receptacles)

    -- self-monitor for symptoms and seek re-evaluation if respiratiory symptoms recur or worsen

There is also comment on the potential of healthcare worker staffing shortages, suggesting that some workers may be able to return to work earlier than as recommended above, per their local occupational health/state authorities. though they should adhere to the recommendations above. For prior CDC guidelines for the assessment of risk, monitoring, and work restriction, see https://www.cdc.gov/coronavirus/2019-ncov/hcp/guidance-risk-assesment-hcp.html

-- those who were never tested but have an alternate diagnosis such as positive test for influenza, criteria for return to work should be based on that diagnosis

 -- and, the test for the SAR-CoV-2 virus has been simplified to include a single nasopharyngeal swab

----------------------------------------------------------------------------------------

 

there was a brief summary of the stability of SARS-CoV-2 on surfaces as well as an aerosol in http://gmodestmedblogs.blogspot.com/2020/03/covid-19-update-31120.html, but I would like to review that article in more detail now that it has been published formally in NEJM (see covid virus longevity surfaces nejm2020 in dropbox, or DOI: 10.1056/NEJMc2004973)

Details:

-- they compared both the new SARS-CoV-2 and the earlier SARS-CoV-1, assessing their viability in 5 environments: aerosols (<5 mm), plastic (polypropylene), stainless steel, copper, and cardboard

-- aerosols: 65% relative humidity, 22°C, small particles were generated through a nebulizer and fed into a Goldberg drum to create the aerosolized environment. Results measured for 180 minutes

-- for the solid surfaces, 40% relative humidity, 22°C, inoculum of 10⁵ TCID per mL (titers were measured in 50% tissue-culture infectious dose: TCID). Which translates to 50 µL of virus put on the surface of these solids and recovered at predefined time points by adding 1 mL of DMEM (Dulbecco’s Modified Eagle Medium, which supports the growth of many different types of cells). Results measured over 7 days

Results:

-- aerosol: SARS-CoV-2: >3 hours (sampling stopped at 3 hours), similar to SARS-CoV-1

    -- there was a very gradual decay over the 1^st 3 hours for both viruses, with the titer of viable virus continuing in the 10³/L range at 3 hours

    -- median half-life of SARS-CoV-2 was 1.1 hours

-- plastic: 72 hours

    -- there was no real difference in titer over the 1^st 8 hours for both viruses at around 10³ /L, then a steeper decline but detectable virus up to 42 hours, decreasing to near 0 at 72 hours.

    -- Median half-life of SARS-CoV-2 was 6.8 hours

-- stainless steel: 72 hours

    -- steep decline for both viruses, being virtually undetectable around 50 hours

    -- median half-life of SARS-CoV-2 was 5.6 hours

-- copper: 4 hours, though 8 hours for SARS-CoV-1

    -- steep decline for both, going from 10⁴ to titer of 700 within 4 hours, then leveling off at that level

    -- median half-life of SARS-CoV-2 was 0.8 hours

-- cardboard: 24 hours, though 8 hours for SARS-CoV-1

    -- rapid decline for both, especially for SARS-CoV-1. For SARS-CoV-2, negligible titer at 24 hours

    -- median half-life of SARS-CoV-2 was 3 hours

Commentary:

-- both viruses have had exponential decay in titer in all of the experimental conditions, reflected as linear decreases in their log graphs

-- overall both viruses decayed similarly, reinforcing that the epidemiologic differences between the two likely arise from other factors, such as differences in viral load (overall SARS-CoV-2 has 1000 times the viral load) as well as timing of shedding (SARS-CoV-2 has major viral shedding early on, even before symptoms; SARS-CoV-1 was later, in the highly symptomatic stage)

-- not sure why they didn’t have longer assessment time for aerosols.  For some reason I was stopped after 180 minutes, though over that three-hour time there was very little decline in the titer

-- it is likley that virus survival may be quite different in different settings: aerosolized particles might have very different half-life in a larger environment than the Goldberg drum (whatever that is), and being exposed to UV light. And the real world will have air turbulence (eg, people moving in the room, perhaps air movement from opening doors, HVAC systems,etc.)  Also, not sure what the decline in viral titers is with distance from the source: does it reduce to zero after 2 feet? 3 feet? the current social distancing suggestion of 6 feet?.  for solids, there may be real differences between the esxperimental conditions and the real-world as well. there are different cardboards with different absorption properties for droplets, different plastics, perhaps the surfaces have some water or dust or cleaning fluid on them or are tarnished....

    --ie, the above half-lives are only estimates and should not be translated absolutely to the real-world (which, for better or worse, is where we live)

--and, there is a real information deficiency (at least to what i have seen): we do not know the concentration of viral particles that are necessary to cause clinical infection. at least for other infections, it is clear that the intensity of the viral exposure is important, and under a certain amount, infection does not occur.  For example, data from China suggest that a small number (around 1% of infections) are asymptomatic, suggesting that the baseline viral load is reall high (and we know that in infected people by day 4 they have 1000x the viral load of the old SARS virus), and/or that the new SARS-CoV-2 is more infectious even with waning titers. but it would be necessary to have information on the disease-inducing inoculum size to interpret the titer values in the above study.  and, of course, that titer threshold may vary from person to person, depending on age, immune status, comorbidities, medications, social conditions (eg crowding in housing...)

    --one possible example of the differential infectivity of SARS-CoV-2 is that those getting the infection from the fish market were at higher risk of severe infection than those by community spread (eg see http://gmodestmedblogs.blogspot.com/2020/03/covid-ace2-ibuprofen-and-grasping-for.html ). This raises the question whether the viral dose was higher via the animal to the human spread??

so, interesting stuff. the issue of prolonged aersolization is particularly concerning, though there are concerns about the real-world reliability of the experimental conditions in the above study. But it certainly elevates the concern that the virus is in the air, that we (and non health care folks) should not wear masks only when around a coughing person (esp in higher risk settings, like doing paperwork/computer work at a health center: probably best just to wear the N-95), and that social distancing is really important (6 feet is probably a good guess, but who knows??). And, that places where the 6 feet is not doable (eg public transportation) deserve special attention. for example, at our health center we are (appropriately) canceling/postponing appointments in those who do not really need to be seen. maybe the bar on that should be even lower in those who use public transportation.  and, if we do have people come in using public transportation, are we inadvertantly reinforcing that it is okay to use that in other circumstances as well??

and, it is good to have some further guidance on when we can stop the home isolation in those with presumed or documented infection

geoff​

If you would like to be on the regular email list for upcoming blogs, please contact me at gmodest@uphams.org

For access to the dropbox, go to link: https://www.dropbox.com/sh/0bmvtita8mzms11/XDTwHySFFg

Then go to "clinic", then to either "clinical stuff" for articles, or "powerpt presentations" for the powerpoint presentations

to get access to all of the blogs:

1. go to http://gmodestmedblogs.blogspot.com/ to see them in reverse chronological order

2. click on 3 parallel lines top left, if you want to see blogs by category, then click on "labels" and choose a category​

3. or you can just click on the magnifying glass on top right, then  type in a name in the search box and get all the blogs with that name in them

please feel free to circulate this to others. also, if you send me their emails, i can add them to the list