Viral DNA shed from monkeypox patients has been found on multiple surfaces in specialist hospital isolation rooms, as well as on personal protective equipment (PPE), and in air samples, according to the latest study from the Liverpool School of Tropical Medicine, the University of Oxford, and the UK Health Security Agency (UKHSA).
The UKHSA recommends that patients with severe monkeypox requiring hospital admission are cared for in isolation rooms, with infection prevention and control (IPC) precautions that aim to contain potentially infectious virus within the room and protect staff who enter. However, to date it has been unclear whether these measures are proportionate to the potential virus exposure risks.
For the study, published in The Lancet Microbe, researchers aimed to measure the extent of environmental contamination with monkeypox virus DNA in five respiratory isolation rooms occupied by six patients with severe laboratory-confirmed symptomatic monkeypox admitted to the Royal Free Hospital in London between May 24 and June 17, 2022.
The team undertook 73 environmental surface swabs of high-touch areas in the five rooms, as well as floors of anterooms, air vents, and bathrooms; and of the PPE of health-care workers in doffing areas in three rooms. They also assessed air samples collected before and during bedding changes in all five rooms.
Samples were analysed using quantitative PCR to assess monkeypox virus contamination levels, and virus isolation was performed to confirm presence of infectious virus in selected positive samples.
Most Environmental Samples Positive for Viral DNA
Results revealed viral DNA on multiple surfaces in the isolation rooms, with 56 of 60 (93%) samples positive by PCR. Monkeypox virus DNA was also found on PPE worn by healthcare workers caring for the patients, and in the anterooms where they removed their PPE.
"Monkeypox virus can be shed into the surrounding environment by people who are infected, particularly in shed skin particles and in debris from monkeypox skin lesions and scabs," the researchers said.
In addition, 5 of 20 air samples taken within the isolation rooms were positive for monkeypox virus DNA, and changing bed linen appeared to increase the likelihood of monkeypox virus entering the air.
"This suggests that viral particles, probably in shed skin particles, can become suspended in the air when bed sheets are changed," the authors said.
They also found that in two of four PCR-positive samples selected for virus isolation, including air samples collected during the bed linen change, the viral particles were capable of replicating in cells under laboratory conditions. This is the first time that replication-competent monkeypox virus has been found in air samples taken around patients hospitalised with monkeypox, the researchers said – it is not just 'dead' virus.
"The virus is relatively hardy and under appropriate conditions can remain infectious on surfaces for weeks, creating a potential infection risk to others," they said.
"These results suggest that monkeypox virus shed into a hospitalised patient's environment poses an infection risk that needs to be managed," said lead author Dr Susan Gould, from the Liverpool School of Tropical Medicine.
"Our results found that changing a patient's bedding appears to be particularly associated with an increased ability to detect monkeypox virus in air samples," she said.
"In 2018, a UK healthcare worker was thought to have developed monkeypox after being exposed to the virus while changing a patient’s bedding, before monkeypox had been considered and diagnosed.
"Our results suggest that changing bed linen used by hospitalised patients with monkeypox does indeed increase the risk of exposure to virus, by disturbing virus on bed linen and allowing it to be suspended in the air."
Results Support Infection Control Measures
She added: "In the context of ward-based care, our results support IPC measures designed to protect against exposure to infectious virus on surfaces and in the air, such as appropriate PPE, as well as applying measures designed to contain shed virus within hospitalised patients' isolation rooms, including the use of negative pressure rooms and doffing areas."
Senior author Dr Jake Dunning, consultant in infectious diseases at the Royal Free Hospital in London, said: "It is important to note that detection of virus, even when demonstrated to be infectious, does not necessarily mean that exposure to the virus in real life would result in infection of the exposed person. However, it does reveal a potential transmission risk and one that is reasonable to control in hospital settings.
"Our results confirm that the strict IPC measures we follow in specialist infectious diseases centres are necessary and appropriate."
However, the team cautioned that their investigation specifically evaluated exposure risks when caring for patients admitted to specialist facilities in hospitals. "The results and recommendations may, therefore, not apply to other settings, such as outpatient clinics where patients attend for a short time, interactions differ, and the virus is unlikely to accumulate to such an extent."
Airborne Transmission not Supported
They added: "There is no suggestion that transmission of monkeypox virus via aerosols is a common way for the infection to spread from one person to another."
In a linked editorial, Dimie Ogiona, professor of medicine and infectious diseases at the Niger Delta University in Nigeria, and Folasade Tolulope Ogunsola, professor of clinical microbiology at the University of Lagos in Nigeria, said: "Historically, fewer than a dozen cases of health care-associated human monkeypox have been reported in endemic African countries."
Furthermore, among monkeypox cases exported to countries outside Africa between 2003 and 2021, at least 250 health-care workers have had variable unprotected exposures to the monkeypox virus in the hospital setting – yet "only one case of nosocomial transmission has been reported in the literature".
They said that the new study findings "further substantiate the potential of the monkeypox virus to contaminate diverse environmental surfaces within and outside the immediate vicinity of the patient care environment.
"The identification of viable monkeypox virus in air samples during bedding changes is novel and noteworthy, especially as the only confirmed case of healthcare-associated monkeypox in non-endemic countries was associated with the changing of bedding in a patient room.
"However, this finding must be interpreted with caution as only one air sample from one patient room yielded replication-competent virus, and the identification of viable virus does not necessarily translate to potential aerosol transmission of monkeypox virus in human populations."
While they recommended suitable precautions – including surface cleaning of hospital rooms and households of patients diagnosed with monkeypox, as well as appropriate PPE for healthcare staff – "further studies are needed to understand the infectious potential of fomites and aerosols in the transmission of monkeypox virus in patient-care settings", they said.
"Until asymptomatic aerosol-related transmission is proven, current epidemiological data does not support airborne transmission of the monkeypox virus."
The authors have declared no competing interests.
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