Fact Check-Updated CDC guidance on monkeypox transmission still includes ‘respiratory transmission’

Social media posts flagging a shift in language about how monkeypox spreads by the U.S. Centers for Disease Control and Prevention (CDC) as evidence of “lies” by the agency are missing the context that in the current monkeypox outbreak, respiratory transmission has been a less important route than was seen in the past.

The posts noting that “respiratory transmission” is no longer listed as a “primary” means of spread also confuse the meanings of respiratory transmission and “airborne” disease spread. Current and past CDC materials do list “respiratory” transmission as one way the virus can be spread, but do not describe the virus as “airborne.”

A post on Twitter (here) shared more than 2,000 times exclaims: “Good Gd. Here is the archived @CDCgov #Monkeypox page before it was scrubbed. AIRBORNE (respiratory) IS PRIMARY MODE OF TRANSMISSION. Just like COVID. The science doesn’t change; only the story does! H/T @J30607610 #MonkeyPoxIsAirborne #CDCLies.”

The post includes a screenshot of archived CDC travel-health guidance that says transmission from animal to human is the most common route, after that, “monkeypox spread from person to person is primarily respiratory.”

The same person then adds a post with a link to the archived CDC travel health webpage (here), which had last been updated in June 2019. Another link is to a current CDC monkeypox FAQ page (here), updated July 29, 2022.

The current FAQ page includes the text: “Monkeypox spreads in different ways. The virus can spread from person-to-person through direct contact with the infectious rash, scabs, or body fluids. It also can be spread by respiratory secretions during prolonged, face-to-face contact, or during intimate physical contact, such as kissing, cuddling, or sex.“

A CDC spokesperson told Reuters, “The latest and best information on how monkeypox spreads is available” on the Monkeypox page of the agency’s website (here).

That page also notes that scientists are still researching some questions, including “How often monkeypox is spread through respiratory secretions, or when a person with monkeypox symptoms might be more likely to spread the virus through respiratory secretions.”

The CDC spokesperson declined to comment on when or why guidance language about respiratory transmission changed.

The “respiratory secretions” language used in newer CDC guidance encompasses the standard meaning of the phrase “respiratory transmission” used in older guidance. Respiratory transmission refers to spread from person to person via “respiratory droplets” of secretions like mucus and saliva typically expelled by coughing and sneezing. These larger droplets can come into contact with another person’s mucus membranes directly or fall on surfaces where they can be later picked up and transferred to the face (here). Influenza is a virus thought to be primarily transmitted via respiratory droplets.

In contrast, “airborne transmission” – also known as “aerosol transmission” -- traditionally refers to much tinier “aerosolized” droplets that can linger in the air for extended periods, making it possible to contract a virus like measles in a room where an infected person has been, for example, without having direct contact with that person (here) .

The distinction between “airborne” or “aerosol” transmission versus “respiratory” transmission is important in healthcare settings where different levels of protective gear and precautions would apply. But there is also debate predating the COVID-19 pandemic and the current monkeypox outbreak about whether even traditional “respiratory” modes of transmission, such as a bout of coughing, can expel some tiny aerosols in addition to large droplets (here).

The primary mode of transmission - whether “airborne” or “respiratory” - is also important in modeling to predict where and how fast a disease will spread (here) and (here). Measles is a classic example of an “airborne” virus that spreads rapidly, with each infected individual causing up to 18 new infections (here). Seasonal flu, thought to spread mainly by “respiratory” transmission, averages one to two new infections for each case (here).

In the current monkeypox outbreak, researchers have so far estimated that each case gives rise to approximately 1.1 to 2.4 new cases (here). In Spain, for example, 1.8 new cases were linked to each case, while in the UK the figure is 1.6, and in Portugal, 1.4, according to World Health Organization data (here).

While respiratory transmission is still among the possible ways of spreading monkeypox in the current CDC guidance, the new language no longer describes it as the “primary” means of transmission.

The CDC spokesperson told Reuters in early August 2022 that in the current monkeypox outbreak, close physical contact has been the primary route of transmission seen. “Of the cases that we have information for, 98.4% reported male-to-male sexual contact, reinforcing that spread during this outbreak is likely happening through close, personal, often skin-to-skin contact,” based on data the agency presented to clinicians at the end of July.

CDC scientists and others have noted publicly that the current transmission patterns with monkeypox mark a change from what had been seen in previous outbreaks. In May, the author of the archived CDC page that had highlighted respiratory-droplet transmission as a “primary” means of person-to-person spread told the online publication STAT that researchers were already rethinking what they had previously assumed about monkeypox (here).

In a mid-July presentation to an American Medical Association audience, CDC scientists also talked about how understanding of monkeypox was changing (here). “This current outbreak is turning much of what we thought we knew on its head,” said Captain Jennifer McQuiston, a veterinarian with the U.S. Public Health Service and part of the CDC’s monkeypox response team. Historically, monkeypox infections were linked directly to animal contact, she explained, and there was little onward transmission. "We had not previously thought of monkeypox as having such a degree of sustained person-to-person spread before or thought of monkeypox as potentially a sexually transmitted or intimate-contact type of infection, although we knew close contact could spread it,” McQuiston said.

A U.S. Department of Homeland Security (DHS) document published in July 2022 citing multiple sources also notes, “Person-to-person transmission has been reported in previous outbreaks but was not common” (here)

Reuters has previously factchecked claims about monkeypox spreading via respiratory routes, and experts agreed that it likely does spread through respiratory droplets, but that there is as yet no evidence for aerosol or “airborne” spread (here).

“Precise language is really important here,” Dr. Hugh Adler of the Respiratory Infections Group, Liverpool School of Tropical Medicine, told Reuters in June. “Respiratory droplet transmission is very different to aerosol/airborne transmission,” he said.

“Monkeypox probably does transmit via large respiratory droplets (same as a number of non-respiratory viruses, e.g. chickenpox), though it is likely that direct close contact (with a patient, including but not limited to sexual contact, or with their shed skin/bedding etc.) is a more important driver of transmission. Large droplets travel about 1 metre in the air before falling to the ground. Tiny aerosols (airborne particles) from the lower respiratory tract remain in the air for longer - there is currently no evidence for monkeypox being transmitted via this route,” Adler said.


Missing context. CDC guidance continues to include respiratory-droplet transmission as a way that monkeypox can spread from person to person, and clarifies that respiratory transmission refers to contact with respiratory secretions. The agency’s current and past guidance documents do not include aerosolized virus or airborne transmission as known routes of transmission. Posts on social media are likely conflating aerosol or airborne transmission with respiratory-droplet transmission.

This article was produced by the Reuters Fact Check team. Read more about our work to fact-check social media posts here .