On Friday, officials from the Centers for Disease Control and Prevention pushed back on the idea that the monkeypox virus could spread through the air, saying the virus is usually spread through direct physical contact with wounds or contaminated materials. of a patient.
The virus can also be transmitted through respiratory droplets expelled by an infected patient who comes into physical contact with another person, they said. But he cannot linger in the air for long distances.
Experts on airborne virus transmission didn’t disagree, but some said the agency hadn’t fully considered the possibility that respiratory droplets, large or small, could be inhaled from a closer distance. a patient.
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The World Health Organization and several experts have said that although “short-range” airborne transmission of monkeypox appears to be rare, it is possible and warrants precautions. Britain also includes monkeypox on its list of “severe consequence infectious diseases” that can spread through the air.
“Airborne transmission may not be the dominant route of transmission, or very efficient, but it can still occur,” said Linsey Marr, airborne virus expert at Virginia Tech.
“I think the WHO is right and the CDC message is misleading,” she added.
In the United States, the monkeypox outbreak has risen to 45 cases in 15 states and the District of Columbia, CDC officials said at a news conference. The global tally has risen rapidly since May 13, when the first case was reported, to more than 1,450. At least 1,500 cases remain under investigation.
Historically, people with monkeypox have reported flu-like symptoms before a characteristic rash appears. But some patients in the current outbreak developed the rash first, and some didn’t have those symptoms at all, CDC director Dr. Rochelle Walensky said Friday.
No deaths have yet been recorded in the current outbreak, she said.
Questions about airborne transmission of monkeypox virus are important because the answers, in turn, will focus on recommendations for masking, ventilation and other protective measures if the outbreak continues to grow.
The CDC said Thursday that monkeypox “is not known to persist in the air and is not transmitted during short periods of shared airspace.” The statement followed a New York Times article on Tuesday in which scientists described uncertainties about the transmission of the virus.
“What we do know is that people diagnosed with monkeypox in this current outbreak have described close and sustained physical contact with others infected with the virus,” Walensky said Friday. “This is consistent with what we have seen in previous outbreaks and what we have known from decades of studying this virus and closely related viruses.”
But monkeypox is poorly studied, other experts said, and occasional episodes of airborne transmission have been reported for the closely related smallpox virus. During a 2017 monkeypox outbreak in Nigeria, infections occurred in two health workers who had no direct contact with patients, scientists told a recent WHO conference.
A few patients in the current outbreak do not know when or how they contracted the virus, CDC officials acknowledged.
The agency is right to reassure the public that the epidemic is not a threat to most people because monkeypox is not as contagious as the coronavirus, said transmission expert Dr Donald Milton of viruses by air at the University of Maryland.
Airborne transmission is unlikely to be a risk to anyone other than immediate caregivers, Milton said, but warned that denying the possibility completely “is the wrong way to do it”.
When a virus is present in saliva or the airways, as monkeypox has been shown to be, it can be expelled in respiratory droplets by speaking, singing, coughing or sneezing, have said Milton and other experts.
Droplets can be heavy and fall quickly on objects or people, or they can be small and light, lingering in the air for long periods of time and over long distances. The CDC’s assessment depends in part on whether the virus is present only in large droplets or also in very small ones, called aerosols.
A similar debate unfolded at the start of the coronavirus pandemic, when the agency and the WHO focused on large droplets as the main route of transmission. But aerosols have proven to be a major driver.
The CDC’s new monkeypox guidelines describe the respiratory droplets emitted by patients as “secretions that rapidly escape from the air.”
But the virus “can be present in respiratory particles of any size”, not just large droplets, said Lidia Morawska, an air quality expert at Queensland University of Technology in Australia.
“In my opinion, there is no basis for the assertion that the virus is transmitted only by large droplets and only poses a risk of infection over short distances,” she wrote in a E-mail.
Patients in the current outbreak appear to have been infected through close and sustained contact, CDC officials said Friday. But this can be difficult to determine.
When people are in close contact, it can be impossible to distinguish whether a virus has been transmitted by touch, spraying large droplets or inhaling aerosols, Marr said.
“The occurrence of transmission in such situations does not define how the virus passed from person to person,” she said. If transmission can occur by spraying respiratory droplets, “then it almost surely also occurs by inhalation of aerosols.”
Yet most experts agree that regardless of the contribution of inhaled aerosols, monkeypox does not appear to be transmitted over the distances that the coronavirus or measles virus can.
“I agree that most monkeypox transmission occurs through touch – most likely direct mucosal contact,” Milton said.
But the “CDC seems to be stuck on old terminology,” he said. “We really need to talk about transmission using terms that clearly say how it happens – by touching, spraying or inhaling.”
The CDC acknowledges the possibility of short-range airborne transmission in its guidance to clinicians. The agency recommends that patients wear masks and that the healthcare staff caring for them wear N95 respirators, which are needed to filter aerosols.
It also warns that “procedures that may spread oral secretions should be performed in an airborne infection isolation room.”
There is evidence that monkeypox can survive in aerosols and that inhaled virus can cause disease in monkeys. However, airborne transmission may not be ideal for monkeypox virus.
Patients may not release much virus in aerosols, the virus may not stay infectious for long, or the amount of inhaled virus needed to infect someone may be too high, Marr said.
If so, airborne transmission is likely to occur only among close people for long periods of time. Yet British health officials, like those in the United States, said many patients did not appear to know when or where they might have been infected.
If they got infected without close contact, “it’s possible airborne transmission happened more than we realize,” Marr said.
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