COVID: Infection by multiple very brief exposures

 The MMWR just released a case report suggesting the inadequacy of their prior advisory to avoid exposures of distancing less than 6 feet for more than 15 minutes (see https://www.cdc.gov/mmwr/volumes/69/wr/mm6943e1.htm?s_cid=mm6943e1_w )

 

Details:

-- a 20-year-old male correctional officer in Vermont was found to have symptomatic Covid-19 on August 11

-- on July 28, he had multiple brief encounters with 6 incarcerated or detained persons (IDPs) who were asymptomatic but in the process of having PCR-based SARS-CoV-2 testing; these 6 people arrived from out-of-state correctional facility on July 28 and were housed in a quarantine unit

-- on July 29, all 6 IDPs tested positive for SARS-CoV-2

-- contact tracing was done by the Vermont Department of Health and the Vermont Department of Corrections, finding that this correctional officer did not meet the Department of Health definition of close contact (within 6 feet of infected person for more than 15 consecutive minutes), so he continued to work

-- on August 4, the corrections officer developed symptoms of loss of smell and taste, myalgia, runny nose, cough, shortness of breath, headache, loss of appetite, and GI symptoms; he subsequently tested positive for coronavirus

-- the corrections officer had 2 contacts outside of work, both of whom were negative; and, he had not traveled outside of Vermont during the 14 preceding days

-- review of videotape footage of the correctional officer documented that he had 22 episodes of close contact (within 6 feet) of an infectious person, all less than 1 minute long, with a total of approximately 17 minutes of cumulative contact. and all on July 28

-- during several of these brief contacts, the IDPs did not wear masks; however, the correctional officer wore a microfiber cloth mass, gown, and eye protections (goggles) during all interactions, and gloves during most

-- in addition, among 7 employees who did meet the formal close contact definition above (i.e. at least 15 minutes of contact), one person received a positive result

 

Commentary:

-- it does seem rather likely that the corrections officer did get Covid-19 from these IDPs, in part by the history as noted above, and in part by the fact that the Covid caseload in Vermont has been historically extremely low, particularly in the timeframe above (20 cases per 100K people)

-- early on, the CDC proposed that close contact for Covid-19 was defined as under a 6-foot distance for more than 15 minutes. The WHO defined it as being within 6 feet for a period of 10 to 30 minutes, or more depending on the exposure. My recollection is some countries even used 30 minutes as the cutpoint

-- this current episode suggests that one could get SARS-CoV-2 with briefer contact than 15 minutes, even when wearing full personal protective equipment. And, this was also another example of transmission from an asymptomatic person.

-- other blogs of suggested that the 6-foot distance also may be inadequate: see http://gmodestmedblogs.blogspot.com/2020/08/covid-transmission-and-distancing.html

 

-- There are many unknowns about viral transmission, including what the necessary viral inoculum is (though it seems that in the UK they are about to perform a seemingly unethical study of intentionally inoculating young people with various quantities of virus and checking the responses, see https://www.nature.com/articles/d41586-020-02821-4 )

    --so, there needs to be some perhaps arbitrary definition of what defines a close contact who needs to be evaluated

    --hence, the within 6-feet for 15 minutes definition, based on understanding of aerosol spread of other viruses. though the 6-foot distance, per above, may well be inadequate given the variability of both the infected person's situation (were they coughing or sneezing or singing or shouting) and the ambient conditions (was there poor ventilation indoors vs outdoors with good ventilation).  And these conditions may change dramatically in the upcoming winter, when there will be more coughing because of other winter viruses and more indoor contact with poorer ventilation because of the weather.  maybe the 6-foot limit needs to be assessed further as well...

Addendum:   The CDC apparently later that day (both publications were from October 21) amended their definition of close contact to be "someone who was within 6 feet of an infected person for a cumulative total of 15 minutes or more over a 24 hour period starting from 2 days before illness (or for asymptomatic patients, 2 days prior to test specimen collection) until the time the patient is isolated", and this is "irrespective of whether the contact was wearing respiratory PPE""  see https://www.cdc.gov/coronavirus/2019-ncov/daily-life-coping/contact-tracing.html . my emphasis added

also, a cautionary note that the outcomes of Covid-19 infection might be worse in those with winter-related concomitant viral infections around (eg influenza A, rhinovirus, RSV): see http://gmodestmedblogs.blogspot.com/2020/07/covid-worse-outcomes-with-other-viral.html

geoff

 

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