Today we're addressing a question that's been at the forefront of many of our minds as we've been caring for COVID patients: we're talking all about healthcare worker infections.  Despite an extensive review of the literature, there are still many unanswered questions; but here is what we know so far.

 

By the numbers

• What percentage of total cases are in HCW? The reported figures are highly variable, ranging from 2.5% (reported in California)1 to 20% (reported from Spain)2
  • Close to home in Ontario: 9.6% reported in one study3
• Some groups have tried to determine the occupational exposure-based excess risk. This is a highly relevant figure; it would tell us about the excess risk incurred from working in healthcare settings, above and beyond the general community risk. Here again, however, the data is inconsistent:
  • Minimal excess risk?
    • Observational data from Spain reported that HCW trends followed community infection rates very closely, arguing against significant occupational exposure4
    • A small case report from Switzerland detected no HCW infections after exposures of 15 minutes or less to confirmed positive cases, despite minimal PPE5
  • Significant excess risk?
    • One study identified a 7% increase in absolute risk of infection in HCW compared to non-HCW in a university hospital setting6
    • An interesting study using self-reporting via smartphone found that HCW had a HR of 11.6 (!) for reporting a positive result compared to the general population7
      • This figure was even higher in those reporting inadequate or re-used PPE
    • One reassuring point: there have been some case reports of situations where HCW were exposed with what would be considered inadequate PPE (AGMP without N95), with no subsequent cases in exposed HCW8
  • Mortality in HCW? Reports are highly variable. This is a difficult figure to determine as it really depends on the denominator (widespread availability of testing)
    • Data generally supports lower mortality rate in HCW, which is likely a reflection of more frequent testing (more detection of mild cases); plus potentially also lower age groups, and better access to healthcare9

 

 

Factors affecting HCW infections

• More frequent testing in HCW than the general population
  • 15% tested vs 3% of the general population in Alberta9
• Burden of COVID disease
  • For HCW in areas with low COVID numbers, infections are more likely to have arisen from a community setting9
  • In contrast, in areas with very high COVID prevalence, the workplace exposure is much greater (particularly if paired with PPE concerns and a generally overwhelmed system)2
• Type and location of care: there are conflicting reports about whether "high-risk" places like ICUs and EDs have higher rates of HCW infection
  • In the Chinese epidemic there seems to have been higher HCW infection rates in locations where AGMPs are carried out10
  • In contrast, an NHS survey did not find any difference in HCW infection rates in high vs moderate vs low-risk areas11
    • A few other studies also found no increased risk in groups involved in AGMP, perhaps due to very careful attention to PPE given the recognized risks of these situations12
  • What's more, one study actually found lower infection rates in ICU HCW (2.1%) compared to those on the general wards (4.9-9.7%)6
• HCW roles
  • Most sources seem to indicate higher risk of infection in nursing role compared to physicians – likely a reflection of providing much more direct patient care11,12
    • However, one study reported far more deaths in physicians: physicians accounted for 57% of deaths, despite representing only 22% of cases.13 This may be related to physician demographics, particularly in this Italian cohort.
  • HCW demographics: things that we know are risk factors for more severe disease such as older age and comorbidities14
    • This is particularly true in physicians who have come out of retirement to help with the pandemic15
    • In an analysis of just under 200 physicians deaths worldwide, 40% were in Italy, 90% were male, and the mean age of the cohort was 66 years old12
    • BAME (Black and minority ethnic) HCW seem to be disproportionately affected11
  • Availability of PPE
    • Compared to HCW with access to adequate PPE who were NOT caring for COVID patients, HCWs caring for patients with documented COVID-19 had aHRs for a positive test of 4.83 if they had adequate PPE, 5.06 for reused PPE, and 5.91 for inadequate PPE7
  • Systems factors may also play a role. There is no hard data on this, although some groups have published their protocols for trying to minimize HCW and nosocomial spread16
    • Many familiar measures: daily temperature monitoring, small segregated HCW teams, virtual teaching/meetings, no cross-institution work, etc.
  • Other factors may play a role in severity of disease, particularly in pandemic conditions: HCW sleep (or lack thereof), stress, adequate nutrition, etc17

 

What serology tells us

• There is a fascinating study out of Birmingham18 where they tested 554 HCW who were currently asymptomatic. They tested everyone for both current COVID (with PCR) and prior exposure (with serology). They also asked about viral symptoms in the past several months. They found that:
  • 4% of those tested were PCR positive (current asymptomatic COVID)
  • 24% (!) of those tested had positive serology – indicating previous COVID infection
    • Higher rate in those who endorsed viral symptoms recently (37.5%) vs those who had been totally asymptomatic (17%)
  • Highest rates of seroconversion (about 30%) amongst acute medicine/GIM, and housekeeping
    • Lower rates (13-14%) in EM and critical care
  • BUT: another group in Germany19 did a similar study, looking at seroconversion in 316 HCW with varying levels of contact with COVID patients; and that group only found a 1.6% seropositive rate

 

Secondary infections from HCW

• There is minimal data on secondary attack rate and infection of household contacts
• One recent publication in a general population cited a household attack rate of 4.7%, with no documented asymptomatic transmission20 -> this is reassuring as we expand our bubbles!

 

 

Sources

1. Heinzerling A, Stuckey MJ, Scheuer T et al. Transmission of COVID-19 to Health Care Personnel During Exposures to a Hospitalized Patient - Solano County, California, February 2020. MMWR, Apr 2020, 69(15), 472–476. doi:10.15585/mmwr.mm6915e5
2. Güell O. Spain ranks first for Covid-19 infections among healthcare workers. EL PAIS. Apr 25, 2020. https://english.elpais.com/spanish_news/2020-04-25/spain-ranks-first-for-covid-19-infections-amonghealthcare-workers.html
3. Pelley L. Health-care workers make up 1 in 10 known cases of COVID-19 in Ontario. CBC News (online), Apr 2020. https://www.cbc.ca/news/canada/toronto/health-care-workers-make-up-1-in-10-knowncases-of-covid-19-in-ontario-1.5518456
4. Folgueira MD, Munoz-Ruiperez C, Alonso-Lopez MA et al. SARS-CoV-2 infection in Health Care Workers in a large public hospital in Madrid, Spain, during March 2020. MedRxiv, March 2020. doi:10.1101/2020.04.07.20055723
5. Canova V, Lederer Schläpfer H, Piso RJ et al. Transmission risk of SARS-CoV-2 to healthcare workers -observational results of a primary care hospital contact tracing. Swiss Medical Weekly, Apr 2020,150, w20257–w20257. doi:10.4414/smw.2020.20257
6. Barrett ES, Horton DB, Roy J et al. Prevalence of SARS-CoV-2 infection in previously undiagnosed health care workers at the onset of the US COVID-19 epidemic. MedRxiv, Apr 2020. doi:10.1101/2020.04.20.20072470
7. Nguyen L, Drew D, Joshi A et al. Risk of COVID-19 among frontline healthcare workers and the general community: a prospective cohort study. MedRxiv, May 2020. doi:10.1101/2020.04.29.20084111
8. Ng K, Poon BH, Kiat Puar TH et al. COVID19 and the Risk to Health Care Workers: A Case Report. Ann Internal Med, Jun 2020. doi:10.7326/L20-0175
9. Alberta Health Services. COVID-19 scientific advisory group rapid response report. May 4, 2020. https://www.albertahealthservices.ca/assets/info/ppih/if-ppih-covid-19-hcw-risk-rapid-review.pdf
10. Ran L, Chen X, Wang Y et al. Risk Factors of Healthcare Workers with Corona Virus Disease 2019: A Retrospective Cohort Study in a Designated Hospital of Wuhan in China. Clin Infectious Dis, Mar 2020. doi:10.1093/cid/ciaa287
11. Cook T, Kursumovic E, Lennane S. Exclusive: deaths of NHS staff from covid-19 analysed. HSJ, Apr 2020. https://www.hsj.co.uk/exclusive-deaths-of-nhs-staff-from-covid-19-analysed/7027471.article
12. Kursumovic E, Lennane S, Cook T. Deaths in healthcare workers due to COVID‐19: the need for robust data and analysis. Anesthesia, May 2020. doi:10.1111/anae.15116
13. Lapolla P, Mingoli A, Lee R. Deaths from COVID-19 in healthcare workers in Italy—What can we learn? Infect Control Hosp Epidemiol, May 2020. doi:10.1017/ice.2020.241
14. Hume T. Italian Doctors Are Coming Out of Retirement to Treat Coronavirus — and Dying. Vice (online), Mar 2020. https://www.vice.com/en_us/article/v74jwm/italian-doctors-are-coming-out-of-retirement-to-treatcoronavirus-and-dying
15. Zhan M, Qin Y, Xue X et al. Death from Covid-19 of 23 Health Care Workers in China. New Eng J Med, Apr 2020. doi:10.1056/NEJMc2005696
16. Gan W, Lim J, Koh D. Preventing Intra-hospital Infection and Transmission of Coronavirus Disease 2019 in Health-care Workers. Safety and Health at Work, Mar 2020. doi:10.1016/j.shaw.2020.03.001
17. Wang J, Zhou M, Liu F. Reasons for healthcare workers becoming infected with novel coronavirus disease 2019 (COVID-19) in China. J Hosp Infect, Mar 2020. doi:10.1016/j.jhin.2020.03.002 0
18. Shields A, Faustini S, Perez-Toldeo M et al. SARS-CoV-2 seroconversion in health care workers. MedRxiv, May 2020. doi:10.1101/2020.05.18.20105197v1
19. Korth J, Wilde B, Dolff S et al. SARS-CoV-2-specific antibody detection in healthcare workers in Germany with direct contact to COVID-19 patients. J Clin Virology, May 2020. doi:10.1016/j.jcv.2020.104437
20. Cheng HY, Jian SW, Liu, DP et al. Contact Tracing Assessment of COVID-19 Transmission Dynamics in Taiwan and Risk at Different Exposure Periods Before and After Symptom Onset. JAMA Internal Medicine, May 2020. doi:10.1001/jamainternmed.2020.2020