According to a new study published in JAMA Network Open, SARS-CoV-2 RNA was found in all particle sizes in air samples collected at a nurse's station in a Boston hospital and was genetically identical to human samples from a healthcare-related outbreak.

Report profiles aerosol spread in hospital COVID-19 outbreak
Report profiles aerosol spread in hospital COVID-19 outbreak


Air Sampling During Hospital Outbreak.


Between November 16, 2020, and March 11, 2021, researchers from Harvard, the Veterans Affairs Boston Healthcare System (VABHS), Boston University, and Brigham and Women's Hospital in Boston gathered air samples at a VABHS hospital and long-term care center to detect SARS-CoV-2 RNA.


They employed a microenvironmental cascade impactor to gather airborne particles in three sizes: more significant than 10.0 micrometer (m), 2.5 to 10.0 micrometer (m), and lower than 2.5 micrometers (m). They took samples on a weekly basis, with a gap between December 10, 2020, and January 4, 2021.


From December 27, 2020, to January 8, 2021, the team investigated a COVID-19 epidemic that affected 103 individuals and healthcare professionals (HCP). It started in a medical ward that wasn't dedicated to COVID-19 patients, not long after vaccines were made available to HCP but not to patients. It came first, followed by the Delta and Omicron varieties, believed to spread more quickly.


In "ward A," the outbreak began when a nurse got COVID symptoms 4 days after receiving the first dose of Moderna vaccination and tested positive. This nurse was assumed to be the index case by investigators.


Over the next six days, contract tracing using polymerase chain reaction (PCR) and antigen testing discovered eight more infected nurses and eight infected patients from ward A, as well as two more infected nurses in a second ward (ward B). COVID-19 patients were transferred to ward C, where staff wore surgical masks but no more protective respirators. Outside of their rooms, they wore masks only.


During three days of air sampling at the nurse's station, four infected nurses and seven infected patients were found in ward A. Three nurses and three patients had cycle threshold (Ct) values of less than 24, indicating significant viral load.


One patient, who had a Ct value of 17 (the lower the number, the higher the virus level), would frequently stroll or sit unmasked in front of the nurse's station within 15 feet of the sampler. Furthermore, the researchers claim that station nurses would occasionally remove their masks to drink.


All 3 particle sizes test positive

At the ward A nurses station, the researchers discovered SARS-CoV-2 in all three particle sizes.



SARS-CoV-2 RNA fragments found in the smallest aerosols ((< 2.5 m) inward A had a sequence identity of 100 percent with human samples. Other size particle samples in ward A had a higher genetic link with human samples (2.5 to 10 m, 99.91 percent; larger than 10 m, 99.97 percent) than samples taken on the same dates in ward C (2.5 to 10 m, 99.91 percent; larger than 10 m, 99.97 percent). From a nurses station and a break room, they varied from 99.36 percent to 99.86 percent.


Active surveillance and isolation of infected HCP were related to decreased SARS-CoV-2 RNA in air samples from those units, according to HCP monitoring on chosen units throughout the medical center

.

The researchers found SARS-CoV-2 RNA fragments in 24 of 300 samples (8.0%) in units where HCP were not under surveillance and 7 of 210 (3.3%) in units where they were. Medium-sized particles ranging from 2.5 to 10 m accounted for over half of all positive samples (20 of 38 [52.6 percent]).


Reducing airborne transmission.


"[Hospital-based] transmission of SARS-CoV-2 happened on a medical unit during the coincidental collection of air samples, and multiple observations were compatible with the aerosol transmission," the authors of the study write.



Additionally, they say, "At least six nurses and patients present during the air sample collection had nasopharyngeal samples with a Ct less than 25, a range associated with replication-competent virus shedding, and the majority were early in their illness when viral RNA in exhaled aerosols is most common. Three affected people had substantially identical viral genomes, implying nosocomial transmission from a single source."



Surveillance and isolation of infected HCPs also appeared to minimize virus spread through aerosols, according to the study.



"Improvements in air filtration, ventilation, and masking in common hospital facilities may reduce transmission of SARS-CoV-2 and other airborne respiratory viruses even more," the scientists conclude.