A Pandemic Paradigm Shift in Our Understanding of Transmission

Infection Control Today, Volume 26, Issue 5

The bugs are winning, but only because we are letting them.

The overriding mission of infection preventionists is to contain and stop the spread of disease. Modern day epidemiology has divided the spread of respiratory diseases into categories of airborne and droplet transmission. This dichotomy, along with 2 standards of prevention, persisted up to the COVID-19 pandemic.1 At the beginning of the pandemic, SARS-CoV-2, the virus that causes COVID-19, was thought to spread primarily by large droplets and environmental surfaces. These droplets should be easy to stop, and initial recommendations were made for contact precautions and wearing of surgical masks.However, surgical masks do not fit tight on one’s face. For droplet spread, they work well, but not for aerosolized particles.

Prior to COVID-19, it was believed that aerosols were composed only of small particles, less than 5 microns in size. Although SARS-CoV-2 is approximately one hundredth of a micron in size,2 the virus is primarily spread by respiratory droplets with an estimated minimal size of 9.3 microns.3 But case reports started to emerge that documented transmission over relatively large distances associated with singing in churches4 and loud talking in restaurants.5

In October 2020, after an extensive analysis of research, the National Academy of Sciences concluded that aerosolization can occur with particle size up to 100 microns.6 Apparently, just talking could aerosolize SARS-CoV-2. In addition, not only could larger particles aerosolize, but talking, singing, and coughing produce a wide range of particle sizes.

We were not facing a dichotomy in methods of spread; we were facing a continuum. When a patient coughs or talks, some of the particles will aerosolize while others that are large droplets will splatter the environment. If a patient has tonsillitis from group B Streptococcus or from Staphylococcus aureus (possibly methicillin-resistant S aureus [MRSA]) and coughs, droplets will be propelled into the room. The size of S aureus is 1 micron,7 and some of the droplets can be expected to aerosolize. Thus, a surgical mask with gaping holes on the sides may not be protective.

Wu et al8 reported the aerosolization of Escherichia coli in 3 hospitals in China. The investigators isolated the bacteria in air and documented spread between wards and hospital corridors, which were at least 10 meters apart. Although many strains of E coli are commensal, the bacterium is just 1 plasmid away from transforming into the superpathogen carbapenem-resistant Enterobacteriaceae.9 One might ask, what could have aerosolized E coli? Possibly toilet plumes. This mode of spread has also been postulated for SARS-CoV-2.10

Unfortunately, the United States has been slow in adopting policies and standards that adequately prevent airborne spread. In the 19th century, health care and the public were highly resistant to realizing that cholera outbreaks were not primarily spread by foul air (miasma).11 In modern medicine, we are now reluctant to believe how frequently pathogens can become airborne.

Mitigation of Airborne Transmission

The use of more effective personnel protective equipment (PPE) and upgrading ventilation systems in all public indoor venues is of paramount importance. Improvements in ventilation can be accomplished by increasing complete air exchanges with outdoor air or equivalent air exchanges with high-efficiency particulate air filtration and/or UV light sanitization.

Alondra Nelson, head of the Office of Science and Technology Policy and deputy assistant to the president, has stated that upgrading a building’s airflow to 5 air exchanges per hour reduces the risk of airborne disease transmission by 50% or more.12 For health care settings, facilities should have the equivalent of 12 or more complete air exchanges per hour.13

In public venues, a proxy for determining safe levels of airflow and air exchanges is the measurement of the carbon dioxide concentration in the air.

Outside air has a carbon dioxide (CO2) concentration of less than 500 ppm. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) recommends a steady-state indoor CO2 concentration of 870 ppm.14 The Environmental Protection Agency (EPA) recommends a maximum indoor CO2 level of 1400 ppm.15 A study from Harvard University found large differences in cognition when CO2 levels were raised from 550 ppm to 1400 ppm. However, the Occupational Safety and Health Administration has more relaxed rules, with a maximal allowed average concentration within an 8-hour working period of 5000 ppm.16 Unfortunately, few indoor public venues in the United States meet the ASHRAE or even the EPA-recommended safe levels. Even at levels below 1000 ppm, symptoms of sick building syndrome, such as sore throat and wheezing, can occur.14

The appropriate use of PPE has also become controversial, with many health care facilities still focusing on the prevention of large droplet spread. Recently, several large hospitals were removing N95 masks that patients wore into the facility and replacing them with surgical masks. This was reported by Politico to also have occurred at Massachusetts General Hospital, the previous facility of the director of the CDC.17

A nonfitted N95 mask provides 4 times the protection of a surgical mask.18 Despite this, and the much greater infectivity of the Omicron variant, regulatory agencies still have not recommended N95 masks for all health care workers. One can make a strong case for wearing N95 masks when treating all patients with respiratory illnesses and relegating the use of poorly fitting surgical masks to surgery, during which the main concern is preventing secretions from the surgeon from contaminating the surgical site.

Increasing Health Care–Associated Infections

The pandemic has given us new knowledge to transform infection prevention; however, it has also created additional challenges that have exacerbated the epidemic of antibiotic-resistant bacteria.

A recent report from the CDC compared the standardized infection ratios (SIRs) of health care–associated infections from the years 2019 to 2020.19 The CDC observed significant increases in central line–associated bloodstream infections (CLABSIs), catheter-associated urinary tract infections, ventilator-associated events (VAEs), and MRSA infections, but not in select surgical-site infections and Clostridioides difficile infections. There was also a 14.2% to 36.4% decrease in the number of reporting hospitals during the pandemic.

Large increases in infections were seen in CLABSIs, VAEs, and MRSA, which experienced a 47.0%, 44.8%, and 33.8% increase, respectively. The SIR for these infections increased to a level between 0.97 and 1.39, effectively wiping out any gains achieved since the 2015 baseline that was set at 1.0.

Prevention of these infections requires trained and experienced staff, along with safe staffing levels. Unfortunately, the pandemic has placed tremendous stress on staff, resulting in extremely high turnover rates at many facilities. As pointed out by Lisa Lockerd Maragakis, MD, MPH, senior director of infection prevention at Johns Hopkins Health System, professor of medicine and epidemiology at Johns Hopkins University School of Medicine and the Johns Hopkins Bloomberg School of Public Health, and cochair of the CDC’s Healthcare Infection Control Practices Advisory Committee, during the March 24, 2022, meeting: “One of the main challenges I think that many of us are facing is an almost complete turnover in personal on some of our units.”20

Overuse of Antibiotics

A primary factor that has contributed to the emergence of antibiotic-resistant bacteria is the overuse of antibiotics. Unfortunately, the use of telehealth during the pandemic may have promoted antibiotic overuse. Without a physical examination, it is very difficult to determine if an ear, sinus, or throat infection is present. Video color balance, brightness, and fogging make examinations of cavities difficult at best. In addition, testing for Group B Streptococcus along with bacterial cultures is not relatively available. Ray et al21 found that antibiotic usage for pediatric direct-to-consumer televisits occurred in 52% of the visits versus 31% for primary care–provider office visits.
Concern regarding bacterial coinfections also promotes antibiotic usage. In a review of the literature, Rawson et al found that 8% of patients with COVID-19 developed a bacterial/fungal coinfection compared with 11% of patients without COVID-19. Despite wide empirical administration of broad-spectrum antibiotics in patients with COVID-19, the authors stated there was a paucity of data to support their use.22


There is no doubt that infection preventionists have a herculean task before them. They must advocate for more effective and available PPE, better indoor ventilation, and mechanisms to decrease aerosols created by sinks and toilets. Extensive training of new and temporary staff must be implemented regarding empirical antibiotic usage and infectious disease protocols, along with the education of patients and providers regarding the limitations of telehealth.

No one can be expected to accomplish all of this with prepandemic resources. The first step must be to educate hospital administration regarding the resources required to reverse the increasing rates of antibiotic resistance and to improve infection prevention by implementing the knowledge learned during the pandemic. Only then will an optimal safe workplace be created and the safest possible care be provided to patients.


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  4. Hamner L, Dubbel P, Capron I, et al. High SARS-CoV-2 attack rate following exposure at a choir practice - Skagit County, Washington, March 2020. MMWR Morb Mortal Wkly Rep. 2020;15;69(19):606-610. doi:10.15585/mmwr.mm6919e6
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    transmission of SARS-CoV-2. October 2020. Accessed April 18. 2022. https://doi.org/10.17226/25958https://www.nationalacademies.org/our-work/airborne-transmission-of-sars-cov-2-a-virtual-workshop
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  9. Skalova A, Chudejova K, Rotova V.AAC. 2017.Molecular characterization of OXA-48-like-producing Enterobacteriaceae in the Czech Republic and evidence for horizontal transfer of pOXA-48-like plasmids. Antimicrob Agents Chemother. 2017;61(2):e01889-1916. doi:10.1128/AAC.01889-16
  10. Li YY, Wang JX, Chen X. Can a toilet promote virus transmission? from a fluid dynamics perspective. Phys Fluids (1994). 2020;32(6):065107. doi:10.1063/5.0013318
  11. History: John Snow (1813 -1858). BBC. Accessed April 18, 2022. https://www.bbc.co.uk/history/historic_figures/snow_john.shtml
  12. Let’s clear the air: an OSTP discussion on COVID and clean indoor air. Transcript. Let’s Clear the Air on COVID virtual event. March 29, 2022. Accessed April 18, 2022. https://www.whitehouse.gov/wp-content/uploads/2022/04/03-2022-Transcript-Lets-Clear-the-Air-on-COVID-An-OSTP-Discussion-on-Clean-Indoor-Air.pdf
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  15. Allen JG, MacNaughton P, Satish U, Santanam S, Vallarino J, Spengler JD. Associations of cognitive function scores with carbon dioxide, ventilation, and volatile organic compound exposures in office workers: a controlled exposure study of green and conventional office environments. Environ Health Perspect. 2016;124(6):805-812. doi:10.1289/ehp.1510037
  16. Carbon dioxide. Occupational Safety and Health Administration. Updated December 21, 2020. Accessed April 18, 2022. https://www.osha.gov/chemicaldata/183
  17. Levy R. Politico. Some hospitals ask patients, visitors to remove N95s, citing CDC – Politico. March 16, 2022. Accessed April 18, 2022. https://www.politico.com/news/2022/03/16/hospital-mask-cdc-covid-00017556
  18. Albarracin D, Beford T, Bollyky T, et al. Getting to and sustaining the next normal: a roadmap for living with COVID. The Rockefeller Foundation. Accessed April 18, 2022. https://www.rockefellerfoundation.org/wp-content/uploads/2022/03/Getting-to-and-Sustaining-the-Next-Normal-A-Roadmap-for-Living-with-Covid-Report-Final.pdf
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  20. Maragakis L. Division of Healthcare Quality Promotion (DHQP) Update.Presented at CDC HICPAC Meeting.March 24, 2022; Atlanta, GA.
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