As the CDC graphic above illustrates, when it comes to infectivity, Norovirus is hard to beat. The `accepted’ mode of transmission has long been the fecal-oral route, but over the past few years we’ve seen evidence supporting an `airborne’ or aerosolized transmission.
Last week, a new study was published in Clinical Infectious Diseases that looked for, and found, norovirus in ambient air samples taken at from 8 hospitals, both inside and outside of an infected patient’s room.
First a link to the study, and some excerpts from the abstract and press release, after which I’ll return with more:
Laetitia Bonifait1, Rémi Charlebois1, Allison Vimont2, Nathalie Turgeon1, Marc Veillette1, Yves Longtin3, Julie Jean2,4, and Caroline Duchaine1,5
Methods. A total of 48 air samples were collected during norovirus outbreaks in 8 healthcare facilities. Samples were taken 1 m away from each patient, in front of the patient's room and at the nurses' station. The resistance to aerosolization stress of murine norovirus MNV-1 bioaerosols was also tested in vitro using an aerosol chamber.
Results. Norovirus genomes were detected in 6/8 healthcare centers. The concentrations ranged from 1.35x101 to 2.35x103 genomes per m3 in 47% of air samples. Norovirus MNV-1 preserved its infectivity and integrity during in vitro aerosol studies.
Conclusion. Norovirus genomes are frequently detected in the air of healthcare facilities during outbreaks, even outside patients' rooms. In addition, in vitro models suggest this virus may withstand aerosolization.
An accompanying press release to the CID study states:
According to Professor Duchaine, this previously unknown mode of norovirus propagation could explain why gastroenteritis outbreaks are so hard to contain: "The measures applied in hospital settings are only designed to limit direct contact with infected patients. In light of our results, these rules need to be reviewed to take into account the possibility of airborne transmission of noroviruses. Use of mobile air filtration units or the wearing of respiratory protection around patients with gastroenteritis are measures worth testing."
Currently, the recommendations from the CDC on the Healthcare Worker’s use of PPEs (Personal Protective Equipment) when dealing with Norovirus reads:
- If norovirus infection is suspected, adherence to PPE use according to Contact and Standard Precautions is recommended for individuals entering the patient care area (i.e., gowns and gloves upon entry) to reduce the likelihood of exposure to infectious vomitus or fecal material. (Category IB)(Key Question 1.C.4)
- Use a surgical or procedure mask and eye protection or a full face shield if there is an anticipated risk of splashes to the face during the care of patients, particularly among those who are vomiting. (Category IB)(Key Question 3.C.2.a)
- More research is needed to evaluate the utility of implementing Universal Gloving (e.g., routine use of gloves for all patient care) during norovirus outbreaks. (No recommendation/unresolved issue)
Most of the CDC’s guidance documents for HCWs dealing with Norovirus cases stress patient cohorting and hand hygiene. Respiratory protection isn’t mentioned in any of the following documents.
- Overview: A Norovirus Outbreak Control Resource Toolkit for Healthcare Settings [PDF - 306 KB]
- Poster: What healthcare providers should know [PDF - 185 KB]
- Fact Sheet: Norovirus in Healthcare Facilities [PDF - 419 KB]
Previously, in Vomiting Larry And His Aerosolized Norovirus, we looked at the physics involved in aerosolizing virus particles via projectile vomiting , while in Norovirus: The Gift That Keeps On Giving, we looked at an incident involving a girl’s soccer team where 17 girls were exposed via a reusable grocery bag, likely contaminated from an airborne route.
Assuming more studies showing the aerosolized spread of noroviruses are published, infection control experts may need to revisit the use of some form of respiratory protection (N95, facemasks, etc.) for HCWs caring for infected patients.