Monkeypox Virus - Credit CDC PHIL
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Last summer, long before the international spread of Monkeypox was even suspected, we saw the first imported case of Monkeypox in the United States since the the multi-state outbreak in 2003, in a traveler in Texas who had recently visited Nigeria (see CDC & Texas Confirm Monkeypox In US Traveler ex Nigeria).
Over the previous few years we'd seen a handful of imported cases in the UK, Israel, and even Singapore, raising concerns that Monkeypox might be on the verge of breaking out of Africa (see PLoS NTD: The Changing Epidemiology of Human Monkeypox—A potential threat?).
A second imported case was reported in Maryland last November. But over the past 90 days the U.S. has confirmed more than 10,000 Monkeypox cases, and that number is rising by hundreds every day. Globally, more than 31,000 cases have been reported, and in late July the WHO declared the outbreak a PHEIC (Public Health Emergency of International Concern).
For a virus with a reputation of not transmitting easily, this outbreak is chalking up impressive numbers, which has scientists trying to determine the ways the virus may be spread.
Direct contact with someone who has lesions is still believed to be the primary driver of transmission (see Nature How does monkeypox spread? What scientists know), but increasingly there are concerns over the persistence of the virus in the environment and fomite transmission.
Six weeks ago, in Eurosurveillance: Surface Contamination in Hospital Rooms Occupied by Patients Infected with Monkeypox, we looked at study that found evidence of surface contamination in and around hospital rooms inhabited by Monkeypox patients in Germany, including places not touched by the patient and in the adjacent anteroom where HCWs donned and doffed their PPE.
Among the most contaminated surfaces they found were door knobs, cabinet door handles, faucets, and light switches
Viral DNA may be detected, even when the virus is no longer viable, or in concentrations too low to be infectious. But these researchers were able to successfully isolate viable virus from 3 of the samples, suggesting transmission of the Monkeypox virus by fomite was at least possible.
Yesterday the CDC's EID Journal published a research article on the environmental sampling at the home of last summer's imported case in Texas, which like the above study, found extensive MPXV-WA DNA contamination on both porous (e.g., bedding, clothing) and non-porous (e.g., metal, plastic) surfaces throughout the home.
While we don't know how frequently Monkeypox is transmitted via fomites in the real world, based on the studies we've seen, it is a plausible route of transmission.
Research
Environmental Persistence of Monkeypox Virus on Surfaces in Household of Person with Travel-Associated Infection, Dallas, Texas, USA, 2021
Clint N. Morgan, Florence Whitehill, Jeffrey B. Doty, Joann Schulte, Audrey Matheny, Joey Stringer, Lisa J. Delaney, Richard Esparza, Agam K. Rao, and Andrea M. McCollum
Abstract
In July 2021, we conducted environmental sampling at the residence of a person in Dallas, Texas, USA, who had travel-associated human West African monkeypox virus (MPXV-WA). Targeted environmental swab sampling was conducted 15 days after the person who had monkeypox left the household.
Results indicate extensive MPXV-WA DNA contamination, and viable virus from 7 samples was successfully isolated in cell culture. There was no statistical difference (p = 0.94) between MPXV-WA PCR positivity of porous (9/10, 90%) vs. nonporous (19/21, 90.5%) surfaces, but there was a significant difference (p<0.01) between viable virus detected in cultures of porous (6/10, 60%) vs. nonporous (1/21, 5%) surfaces.
These findings indicate that porous surfaces (e.g., bedding, clothing) may pose more of a MPXV exposure risk than nonporous surfaces (e.g., metal, plastic). Viable MPXV was detected on household surfaces after at least 15 days. However, low titers (<102 PFU) indicate a limited potential for indirect transmission.
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Discussion
In this real-world setting, targeted sampling of high-use surfaces and objects was effective at detecting MPXV DNA and viable virus. MPXV DNA was found throughout the household, indicating extensive spread of viral material, probably a result of the man having an extensive purulent rash develop. Our study demonstrated the ability of MPXV to persist in a household environment for at least 15 days.Previous studies with vaccinia and variola viruses demonstrate the capability of OPXVs to persist in the environment much longer than 15 days (months or years), so potentially the virus sampled in this household could have remained viable for a longer period (10,15,16). A similar investigation had been conducted with a household case of eczema vaccinatum (vaccinia virus), in which household contamination was a concern because of extensive rash (22). That study reported less extensive viral DNA dissemination around the household than what we detected and viable virus from 1 cloth item and 2 nonporous items at 10 days after removal of an infected person (22).
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It is unknown how long the culture-positive materials in this study would remain viable with MPXV because viral titers will decrease over time until undetectable by viral culture. Subsequently, as viral titers decrease, infectivity (capacity to cause secondary infection) would also decrease. In comparable studies of OPXV persistence (Appendix Table), under slightly lower heat and humidity conditions, the maximum duration that virus remained detectable on fabrics ranged from 28 to 70 days (16,32). Considering the low titers observed (<3.2 × 102 PFU/mL) and the high heat and moderate humidity environment, it is probable that maximum persistence of viable virus on the items sampled would fall into a similar range.
This study was conducted alongside a public health response, and priorities were identifying potential high transmission risk areas and objects and confirming presence/absence of viable virus. These results are merely representative of the conditions of each specific item at 1 point in time and not representative of the total potential for fomite transmission within the household from items not sampled. A more robust sampling method would be recommended for future studies, including multiple sampling time points and recording the environmental conditions in the household over time. Household disinfection is recommended for any household occupied by a person confirmed to have monkeypox. A disinfectant registered with the Environmental Protection Agency should be used, such as a disinfectant that has an emerging viral pathogens claim, in accordance with the manufacturer’s instructions (33). Specific recommendations for household disinfection can be found on the CDC monkeypox web page (34).
