Keeping Down Norovirus in a Hospital Setting

Recent vomiting was strongly linked to detecting norovirus RNA during a hospital norovirus outbreak, a small Swedish study found.

A vomiting episode within the last 3 hours was associated with an eight-fold increase in the odds of hospital air samples testing positive for norovirus (OR 8.1, P<0.01), reported Carl-Johan Fraenkel, MD, of Lund University in Sweden, and colleagues.

However, there was no link between an air sample testing positive for norovirus and time since a patient’s last episode of diarrhea, the authors wrote in Clinical Infectious Diseases.

The authors said that outbreaks of norovirus are especially difficult to control in healthcare facilities, causing “severe workflow disruptions, substantial economic costs and excess morbidity.” While contaminated food, water, or contact with contaminated surfaces or infected people have been thought to be the main routes of norovirus transmission, some evidence also suggests it could be transmitted through the air, they said.

“Hypothetically, infectious particles could be aerosolized from for instance vomitus or toilet flushing, deposited in the upper respiratory tract during inhalation, and swallowed,” they wrote. “If this occurs at a significant scale, additional infection control measures may be required to prevent transmission effectively.”

Virus-containing particles under 10 microns can stay airborne for hours, Fraenkel and colleagues noted.

Prior research found evidence of norovirus in hospital air during outbreaks, but “none of these studies provide any information on possible sources of airborne [norovirus] or connection to outbreaks or transmission of infection,” said Fraenkel and colleagues.

For the current study, the group examined air samples from three hospitals in southern Sweden, taken from areas with patients who had suspected norovirus gastroenteritis with ongoing symptoms (defined as diarrhea and/or vomiting in the last 24 hours). Only patients with laboratory-confirmed norovirus were part of the final analysis.

An outbreak was defined as at least two patients on the ward with confirmed norovirus infection, including at least one with “probable ward acquired infection.”

Overall, there were 86 air samples from 13 different hospital wards with 26 patients believed to be infected; the median sample size was three per patient. There was norovirus RNA in 21 of 86 of these air samples related to 10 separate patients. Among 13 control samples, all were negative for norovirus.

Air samples that tested positive for norovirus were found “almost exclusively” during outbreaks, the authors said — with 15 of 26 patients a part of 12 separate outbreaks. These outbreaks involved two to five patients with hospital-acquired norovirus gastroenteritis.

Not surprisingly, there was a significant association between detecting norovirus in the air and a shorter period of time since a patient’s last vomiting episode, even after controlling for diarrhea, with nine of 14 air samples collected within 3 hours of the last vomiting episode testing positive for norovirus.

Moreover, the authors noted that although the particle size differed in the four outbreaks, they found airborne particles that “are easily inhaled and have a typical probability of 10-30% to deposit in the mouth, nose or conducting airways.”

They concluded that their study is the largest study of airborne norovirus, and even though it was not large enough to conduct a multivariable analysis controlling for confounders, “the main findings are valid and generalizable.”

“The finding of airborne [norovirus] in sufficient concentrations to cause disease raises the question if and how to optimize infection control efforts and personal protection equipment,” they wrote. “In view of possible transmission by air, hospital staff and planners should take airflow and ventilation rates into consideration to better prevent this contagious virus.”

last updated 07.01.2019