*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
In a recent study posted to the medRxiv* preprint server, researchers conducted a systematic review to evaluate the effectiveness of case isolation and respiratory interventions in limiting the transmission of mpox in humans.
Background
The mpox virus is a double-stranded deoxyribonucleic acid (DNA) Orthopoxvirus from the Poxviridae family. Mpox as a zoonotic disease has generally been endemic to Africa, with recent increases in incidence after smallpox eradication programs and vaccines were discontinued. The 2022 outbreak in regions outside of the endemic distribution, with the ability to transmit from human to human, resulted in the World Health Organization (WHO) declaring the outbreak a public health emergency.
Mpox presents during the viral invasion period as headaches, lymphadenopathy, fever, myalgia, back pain, and asthenia. About one to three days after the onset of these symptoms, the patient presents rashes on the face, oral mucus membranes, genitalia, and extremities that begin as macules and change into papules and vesicles, eventually presenting as pustules that crust.
The transmission is suspected to be through direct sexual or non-sexual contact, inhalation of fomites and droplets, and through the placenta. Whether the mpox virus can be transmitted through other fluids such as semen, urine, breastmilk, or through insect vectors remains unclear. It is important to understand whether isolation measures and the use of respiratory interventions are successful in limiting the transmission of the virus.
About the study
In the present study, the researchers used a set of research questions proposed by the WHO to conduct their review. The first question aimed to determine whether using a respirator instead of a medical mask reduces mpox transmission when healthcare workers interact with patients. The second question compared the efficiency of an airborne precaution room with that of a well-ventilated room in reducing mpox infections among healthcare workers and patients. The last question assessed whether the isolation of mpox patients until all the lesions are healed reduces the transmission of mpox virus.
The review included studies that involved patients with mpox or mpox-like infections that were laboratory-confirmed and individuals with exposure to mpox or mpox-like infections. The review examined interventions such as respiratory precautions like respirators or medical masks, contact precaution measures such as gloves, eye protection, case isolations, and ventilated rooms including natural and mechanical ventilation options, negative and positive pressure gradients, and ventilated lobbies.
The examined outcomes were an absolute number of secondary mpox or mpox-like infections or secondary transmission rates and any reported adverse reactions to the interventions. The review included randomized controlled trials, observational comparative studies, and before and after controlled studies on confirmed cases or exposure to mpox or mpox-like infections. mpox-like infections were defined as infections due to other human-to-human transmitted orthopoxviruses.
Results
The results indicated that in 61.7% of the cases (2,420 out of 3m924), the transmission occurred through direct sexual contact. No cases were identified where the transmission route was through the inhalation of droplets. Two cases (0.05% of the 3924 cases) where fomites were identified as the single transmission route were also reported.
The findings also indicated that the infectious mpox virus was identified in various studies in saliva, oropharyngeal swabs, and air samples. Eight studies reported successful viral isolation from 48% of lesion samples, while five studies that conducted surface sampling in healthcare and domestic environments detected mpox virus in 16.2% of the samples. However, the authors believe that the detection of mpox virus from environmental and clinical samples provides only a low level of certainty of transmission risk.
The review found a dearth of information on mpox transmission rates among healthcare workers. The few studies that identified mpox transmission among healthcare workers reported transmission through percutaneous injuries or possible fomites. These findings suggested that the impact of respiratory interventions such as masks and respirators might not be significant in reducing transmission, as mpox transmission seems to occur primarily through direct contact.
While covering lesions and preventing the shedding of infectious mpox virus onto surfaces might potentially reduce transmission, the authors believe that isolation of patients might have minimal effect. Factors such as the infecting dose, route of exposure, and how susceptible the exposed individual is might all play a role in the relative transmission risk.
Conclusions
Overall, the results indicated that inhalation of respiratory droplets from infected individuals does not play a role in the transmission of mpox virus. The transmission seems to occur primarily through direct contact, often sexual. While covering the lesions and wearing gloves and masks around patients can reduce transmission rates, isolating individuals with mpox infections does not seem to be a significant benefit.
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
