Asymptomatic and presymptomatic individuals transmit SARS-CoV-2 virus efficiently.
Kimball et al., “Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility — King County, Washington, March 2020,” Morbidity and Mortality Weekly Report (MMWR) 2020;69:377–381, https://www.cdc.gov/mmwr/volumes/69/wr/mm6913e1.htm.
- This study examined infections in a long-term care skilled nursing facility in Washington.
- Researchers found that 56.5% of residents were infected and infectious but asymptomatic at the time of testing. They also note that symptom-based screening of nursing home residents might fail to identify all SARS-CoV-2 infections.
Abkarian et al., “Speech can produce jet-like transport relevant to asymptomatic spreading of virus,” Proceedings of the National Academy of Sciences, September 25, 2020, https://www.pnas.org/content/early/2020/09/24/2012156117.
- This study examined and visualized airflows during breathing and speaking, with a high-speed camera to capture the movement of aerosols.
- Researchers found that normal conversations can create a turbulent, jet-like airflow that can transport exhaled breath over 2 meters (6 feet) in front of the speaker, potentially further, within 30 seconds. The results of this study are relevant to asymptomatic spread of SARS-CoV-2 as transmission can occur in the absence of a cough. It also highlights the importance of the proximity to and time spent with an asymptomatic speaker, especially in indoor settings.
Widders et al., “SARS-CoV-2: The viral shedding vs infectivity dilemma,”Infection, Disease & Health, May 20, 2020, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7237903/.
- This study evaluated the evidence around viral shedding and infectivity of SARS-CoV-2.
- Researchers found that the percentage of asymptomatic SARS-CoV-2 infections range from 1% to 78%. They also found that immunosuppression and disease severity appear to prolong the duration of viral shedding; though, the correlation between duration of shedding and infectivity is unclear.
Long et al., “Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections,” Nature Medicine, June 18, 2020, https://www.nature.com/articles/s41591-020-0965-6
- Researchers compared Covid-19 antibody responses of 37 asymptomatic patients and 37 symptomatic patients in China. They found that asymptomatic group had a significantly longer duration of viral shedding than the symptomatic group. In addition, IgG levels and neutralizing antibodies diminished significantly within 2 to 3 months after infection. No antibodies were detected 8 weeks after recovery in 40% of asymptomatic group and 12.9% of symptomatic group.
Corcorran et al., “Prolonged persistence of PCR-detectable virus during an outbreak of SARS-CoV-2 in an inpatient geriatric psychiatry unit in King County, Washington,” American Journal of Infection Control, August 19, 2020, https://www.ajicjournal.org/article/S0196-6553(20)30806-3/fulltext.
- This study described key characteristics, interventions, and outcomes of a SARS-CoV-2 outbreak within an inpatient geriatric psychiatry unit at the University of Washington Medical Center – Northwest.
- Researchers identified 10 patients and 7 staff members with SARS-CoV-2 infection; 30% of patients remained asymptomatic over the course of infection. The median duration of PCR positivity was 25.5 days among symptomatic patients and 22.0 days among asymptomatic patients. Cycle threshold values (viral load) was similar between symptomatic and asymptomatic patients.
Airborne precautions are needed for Covid-19.
Patients infected with SARS-CoV-2 produce viral particles that can be aerosolized when they breath, cough, sneeze, etc.
Ma et al., “Covid-19 patients in earlier stages exhaled millions of SARS-CoV-2 per hour,” Clinical Infectious Diseases, August 28, 2020, https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1283/5898624.
- Researchers collected exhaled breath condensate from 57 Covid-19 patients, 4 hospitalized non-Covid-19 patients, and 15 healthy individuals in Beijing. Exhaled breath samples had the highest positive rate (26.9%); Covid-19 patients emitted millions of SARS-CoV-2 particles into the air per hour.
- Air samples and surface swabs were also collected from quarantine hotels and hospitals. Toilet room air and surface swab samples were most likely to be positive, followed by hospital floor, other surfaces, patient touching surfaces, and medical touching surfaces.
Wolfel, Roman, et al., “Virological assessment of hospitalized patients with Covid-2019,” Nature, April 1, 2020, https://www.nature.com/articles/s41586-020-2196-x.
- This study examined viral loads and isolates for patients hospitalized with Covid-19. The majority of patients in this study presented with upper respiratory tract symptoms. Viral loads from upper respiratory tract samples were extremely high (more than 1000 times higher than SARS). Live virus was isolated from upper respiratory tract tissues.
- Michael Osterholm, PhD, MPH, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said, “The findings [of this study] confirm that Covid-19 is spread simply through breathing, even without coughing… They also challenge the idea that contact with contaminated surfaces is a primary means of spread,” (emphasis added). http://www.cidrap.umn.edu/news-perspective/2020/03/study-highlights-ease-spread-covid-19-viruses.
Leung, Nancy H. L. et al. “Respiratory virus shedding in exhaled breath and efficacy of face masks,” Nature Medicine, April 3, 2020, https://www.nature.com/articles/s41591-020-0843-2.
- This study examined viral presence and load in exhaled breath of patients with lab-confirmed influenza, seasonal coronaviruses, or rhinovirus.
- Found viral presence in exhaled breath, even without cough, for all types of viruses in both droplet (>5 micron) and aerosol (<5 micron) particles.
Bourouiba, Lydia, “Turbulent Gas Clouds and Respiratory Pathogen Emissions: Potential Implications for Reducing Transmission of Covid-19,” JAMA, March 26, 2020, https://jamanetwork.com/journals/jama/fullarticle/2763852.
- This paper reported on what is known about disease transmission via respiratory droplets created by human exhalations, sneezes, and coughs.
- Droplet transmission was originally defined in 1897, large and small droplets defined in 1930s. This model of infectious disease transmission hasn’t been updated since. And yet, the CDC and WHO maintain use of this paradigm despite more recent research.
- More recent research over the past few decades performed with instrumentation that better measures particle sizes and movement has determined that human exhalations, coughs, and sneezes (the things that supposedly create large droplets under old model) are actually made of multiphase turbulent gas clouds (a puff) that entrains ambient air and traps and carries clusters of particles of a wide range of sizes.
- This includes viral particles in people who are sick.
- Pathogen-carrying gas clouds emitted when people breath, cough, and sneeze can travel up to 23-27 feet.
Morone, et al., “Incidence and Persistence of Viral Shedding in Covid-19 Post-acute Patients With Negativized Pharyngeal Swab: A Systematic Review,” Frontiers in Medicine, August 28, 2020, https://www.frontiersin.org/articles/10.3389/fmed.2020.00562/full.
- Literature review examining 147 studies measuring viral shedding in patients.
- Researchers found variation in length of time patients shed SARS-CoV-2 virus in different body fluids. The fecal viral positivity duration was (median 19 days) longer than respiratory tract viral positivity (median 14 days).
SARS-CoV-2 virus can survive in the environment, including in the air.
Santarpia et al., “Aerosol and surface contamination of SARS-CoV-2 observed in quarantine and isolation care,” Scientific Reports, July 29, 2020, https://www.nature.com/articles/s41598-020-69286-3.
- Researchers collected air and surface samples to examine viral shedding from isolated Covid-19 patients. Significant environmental contamination was found in bedrails, toilets, ventilation grates, window ledges and hallways.
- SARS-CoV-2 was found in air samples taken greater than 6 feet from the patients.
- SARS-CoV-2 was found in air samples worn by sampling personnel, even in the absence of cough.
Santarpia et al., “The Infectious Nature of Patient-Generated SARS-CoV-2 Aerosol,”medRxiv, July 21, 2020, https://www.medrxiv.org/content/10.1101/2020.07.13.20041632v2.
- This study looked at the presence and viral replication of SARS-CoV-2 in aerosol samples around 6 patients admitted into mixed acuity wards in April 2020. Samples were collected greater than 6 feet from patients, beyond the foot of the bed.
- SARS-CoV-2 RNA was found in respired aerosols <5 µm around all 6 patients. When placed in cell cultures, aerosol samples <1 µm in diameter replicated.
- Researchers note that the study shows that some aerosol particles smaller than 5µm produced through normal breathing, vocalization, and coughing can contain infectious SARS-CoV-2.
Kasloff, Samantha B., et al., “Stability of SARS-CoV-2 on Critical Personal Protective Equipment,” medRxiv, June 12, 2020, https://www.medrxiv.org/content/10.1101/2020.06.11.20128884v1.
- Studied how long SARS-CoV-2 virus can survive on different surfaces in the healthcare environment , including nitrile medical examination gloves, reinforced chemical resistant gloves, N-95 and N-100 particulate respirator masks, Tyvek coveralls, plastic from face shields, heavy cotton, and stainless steel.
- Coupons of each type of material were inoculated with SARS-CoV-2 virus along with compounds meant to mimic the organic components of virus-containing fluid typically shed by patients. Coupons were then dried and maintained at ambient temperature and humidity (35-40%).
- The study found viable virus on the following surfaces for the following time frames (max time studied was 21 days):
- Plastic (from face shield) up to 21 days
- N-95 mask up to 21 days, with significant quantity of virus recovered after 14 days
- N-100 mask up to 21 days
- Tyvek up to 14 days
- Stainless steel up to 14 days
- Nitrile gloves up to 7 days
- Chemical resistant gloves up to 4 days
- Cotton up to 24 hours
- This study starkly underlines the risks of reusing single-use N-95 respirators and other single-use PPE. And it underlines the importance of effective cleaning protocols for powered air-purifying respirators (PAPRs), elastomeric respirators, and other PPE designed for reuse.
Doremalen et al., “Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1,” New England Journal of Medicine, April 16, 2020, https://www.nejm.org/doi/full/10.1056/NEJMc2004973?query=featured_home.
- This study examined how long SARS-CoV-2 can survive in aerosols suspended in the air and on surfaces of different types (metal, plastic, cardboard).
- They found that SARS-CoV-2 can survive up to three hours in aerosols, four hours on copper, 24 hours on cardboard, 2-3 days on plastic and stainless steel.
- The authors conclude, “Our results indicate that aerosol and fomite transmission of [SARs-CoV-2] is plausible, as the virus can remain viable in aerosols for multiple hours and on surfaces up to days.” This study was conducted by NIH and CDC scientists in addition to UCLA and Princeton.
Chin, Alex W H et al. “Stability of SARS-CoV-2 in different environmental conditions,” The Lancet Microbe, April 2, 2020, https://www.sciencedirect.com/science/article/pii/S2666524720300033?via%3Dihub.
- This study examined the ability of SARS-CoV-2 to survive outside the human body in different environmental conditions.
- They found that SARS-CoV-2 can survive outside the human body for up to 14 days at 39 degrees Fahrenheit, 7 days at 72 degrees Fahrenheit and remains infectious in both situations.
- They found that SARS-CoV-2 can survive on different surfaces:
- Printing and tissue papers- up to 3 hours
- Wood and cloth- up to 2 days
- Glass and banknote- up to 4 days
- Stainless steel and plastic- up to 7 days
- Surgical mask- detectable level of infectious virus found after 7 days on outer layer of mask
- They also tested the impact of different disinfectants, used at working concentrations, to successfully inactivate SARS-CoV-2:
- Household bleach (1:49)
- Household bleach (1:99)
- Ethanol (70%)
- Povidone-iodine (7.5%)
- Chloroxylenol (0.05%)
- Chlorhexidine (0.05%)
- Benzalkonium chloride (0.1%)
Fears, Alyssa C. et al. “Persistence of Severe Acute Respiratory Syndrome Coronavirus 2 in Aerosol Suspensions,” Emerging Infectious Diseases, June 22, 2020, https://wwwnc.cdc.gov/eid/article/26/9/20-1806_article.
- This study looked at the viability of SARS-CoV-2 in suspended aerosols and found that SARS-CoV-2 remained infectious after 16 hours suspended in aerosols. This further reinforces airborne/aerosol transmission of SARS-2.
- The authors state: “Our approach of quantitative measurement of infectivity of viral airborne efficiency complemented by qualitative assessment of virion morphology leads us to conclude that SARS-CoV-2 is viable as an airborne pathogen.”
Lednicky et al., “Viable SARS-CoV-2 in the air of a hospital room with Covid-19 patients,” International Journal of Infectious Diseases, September 15, 2020, https://www.ijidonline.com/article/S1201-9712(20)30739-6/fulltext#%20.
- Researchers recovered viable (infectious) SARS-CoV-2 virus in the air from a hospital room with 1 Covid-19 patient and a 2nd patient who had previously tested positive for Covid-19 but tested negative prior to the study. The air was collected 2 to 4.8 meters (6.5 to 15.7 feet) away from the patients.
- Airborne virus was detected in the absence of health-care aerosol-generating procedures.
- The virus strain detected in the aerosols matched the virus strain isolated from a patient with acute Covid-19.
Guo, Zhen-Dong et al., “Aerosol and Surface Distribution of Severe Acute Respiratory Syndrome Coronavirus 2 in Hospital Wards, Wuhan, China, 2020,” Emerging Infectious Diseases, April 10, https://wwwnc.cdc.gov/eid/article/26/7/20-0885_article.
- This study looked at environmental contamination in an ICU and a general ward in hospital in China where patients with Covid-19 were placed.
- They found SARS-CoV-2 on many surfaces in patient rooms and on units, including doorknobs, bedrails, patient masks, computer mouse, keyboards, etc.
- Many positive results on floors not just in patient room but throughout the unit. 50% of the samples from the soles of healthcare workers’ shoes were positive.
- They also measured SARS-CoV-2 in air samples and found several air samples positive in addition to finding that the samples from the air outlets were positive for virus.
- Underlines nurses’ need for PPE!
Santarpia, Joshua L et al., “Transmission Potential of SARS-CoV-2 in Viral Shedding Observed at the University of Nebraska Medical Center,” medRxiv (pre-print), March 26, 2020, https://www.medrxiv.org/content/10.1101/2020.03.23.20039446v2.
- This study looked at the presence of virus in air samples taken in patient rooms in addition to environmental samples.
- SARS-CoV-2 was found in a majority of air samples taken at greater than 6 ft from patient.
- SARS-CoV-2 was found in a majority of hallway air samples.
- SARS-CoV-2 was found in the air samplers worn by sampling personnel even when the patients did not cough.
Updated version posted June 3, 2020 (https://www.medrxiv.org/content/10.1101/2020.03.23.20039446v3):
- Some samples were tested for viral replication/viability and found positive.
- “Despite wide-spread environmental contamination and limited SARS-CoV-2 aerosol contamination associated with hospitalized and mildly ill individuals, the implementation of a standard suite of infection prevention and control procedures prevented any documented cases of Covid-19 in healthcare workers,” based on symptom screening. The infection control and prevention measures in these settings included:
- Negative pressure rooms with 12-15 air changes per hour
- Negative pressure hallways in the suite compared to outside
- Strict access control
- Highly trained staff with well-developed protocols
- Frequent environmental cleaning
- Aerosol-protective personal protective equipment that consisted of either an N95 filtering facepiece respirator or a powered air-purifying respirator (PAPR)
Chia, Po Ying et al. “Detection of Air and Surface Contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Hospital Rooms of Infected Patients” medRxiv April 9, 2020, https://www.medrxiv.org/content/10.1101/2020.03.29.20046557v1.full.pdf.
- This study examined surface and air contamination in airborne infection isolation rooms of patients with confirmed Covid-19 infections in Singapore.
- They found that 56.7% of the rooms had at least one environmental surface contaminated, with 18.5% of the toilet seats and toilet flush button being contaminated.
- High touch surface contamination was shown in ten (66.7%) out of 15 patients in the first week of illness, and three (20%) beyond the first week of illness (p = 0.010).
- Air sampling of two Covid-19 patients (both day 5 of symptoms) detected SARS-CoV-2 PCR positive particles of sizes >4 µm and 1-4 µm. In a single subject at day 9 of symptoms, no SARS-CoV-2 PCR-positive particles were detected.
Protective PPE, including at minimum N95 respirators, gowns/coveralls, eye protection, and gloves, is important to protect nurses and other healthcare workers from exposure to SARS-CoV-2.
Nguyen et al., “Risk of Covid-19 among front-line health-care workers and the general community: a prospective cohort study,” The Lancet Public Health, July 31, 2020, https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(20)30164-X/fulltext.
- This study examined the risk of Covid-19 among healthcare workers compared to the general public as well as the effect of personal protective equipment (PPE) on risk. Researchers used the Covid Symptom Study app which asked daily questions about symptoms, testing, PPE, and exposures.
- They found that frontline healthcare workers with inadequate PPE caring for confirmed Covid-19 patients had 5.91x higher risk of a positive test when compared to healthcare workers with adequate PPE not caring for confirmed Covid-19 patients.
Degesys et al., “Correlation Between N95 Extended Use and Reuse and Fit Failure in an Emergency Department,” JAMA, June 4, 2020, https://jamanetwork.com/journals/jama/fullarticle/2767023.
- This study examined the prevalence of N95 fit test failure while reusing 2 common types of N95 respirators at the University of California, San Francisco.
- Researchers found thatN95s worn for more hours were more likely to fail fit testing (p<0.05),N95s used for more shifts were more likely to fail fit testing (p<0.001), andN95s donned and doffed more times were more likely to fail fit testing (p<0.001).
Chalikonda et al., “Implementation of an Elastomeric Mask Program as a Strategy to Eliminate Disposable N95 Mask Use and Resterilization: Results from a Large Academic Medical Center,” Journal of the American College of Surgeons, June 11, 2020, https://www.journalacs.org/article/S1072-7515(20)30471-3/fulltext.
- This article describes the results from a Pennsylvania hospital system’s widespread implementation of elastomeric and powered air purifying respirators (PAPR) program to alleviate the issues with N95 reusage and resterilization. Researchers reported on their phased-in process, training, education, and fit testing. After conducting a conservative cost analysis, they found that implementation of the elastomeric and PAPR program was 10x cheaper per month than an N95 reuse and decontamination program.
Houlihan et al., “Pandemic peak SARS-CoV-2 infection and seroconversion rates in London frontline health-care workers,” The Lancet, July 9, 2020, https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(20)31484-7.pdf.
- This study examined a prospective cohort study of 200 frontline healthcare workers to evaluate risks.
- Researchers found that 44% of frontline healthcare workers had evidence of SARS-CoV-2 infection either by RT-PCR or serology in London. Evidence of infection among healthcare workers was more than double that of the London population, which highlights the importance of implementing policies to better protect healthcare workers.
Marago, Italo and Minen, Isa. “Hospital-Acquired Covid-19 Infection – The Magnitude of the Problem,” The Lancet Infectious Diseases, July 27, 2020, https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3622387.
- This study examined the prevalence of hospital-acquired Covid-19 infection or nosocomial transmission to patients in England. Patients were divided into two groups (nosocomial vs community). Cases were nosocomially acquired if a patient developed symptoms 7 or more days after hospital admission. Cases were community-acquired if a patient developed symptoms 7 days before hospital admission.
- Researchers found that 16.2% of Covid-19 patients met the criteria for nosocomial infection, the majority of which occurred in “low-risk wards” (suspected and negative Covid-19 zones).