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There is currently no evidence that monkeypox is airborne, CDC officials said on Friday.

To date, 45 cases across 15 states and Washington, D.C. have been reported -- and not all are linked to international travel -- but no deaths have been associated with the outbreak, CDC Director Rochelle Walensky, MD, said on a conference call with reporters.

She reiterated that the virus transmits either through "direct contact" with an infected person via sores on the body, contact with materials that have touched those sores, or "respiratory secretions" during close face-to-face contact. It is unclear whether it spreads through semen or vaginal fluids, or whether asymptomatic people can spread the virus, she added.

However, Walensky noted that monkeypox is not thought to "linger in the air" or spread via "casual conversation" or quick encounters, such as passing someone at the grocery store.

Reporters were quick to point out that this is what CDC said about COVID early in the pandemic.

"All of the cases we've seen to date in this outbreak are related to direct contact, either through skin-to-skin contact or through bed sheets," Walensky said, with the caveat that it is "nearly impossible" to separate skin-to-skin contact via sexual contact from face-to-face contact.

Officials acknowledged the potential for "droplet transmission," similar to COVID, where the virus is transmitted via large respiratory droplets, such as coughing or sneezing, but not merely breathing. Walensky said an airborne virus is usually defined as "small viral particles that become suspended in the air and can stay there for long periods of time."

"We have not seen documentation of that with this virus," she noted.

When pressed by a reporter, Capt. Jennifer McQuiston, DVM, deputy director of CDC's Division of High Consequence Pathogens and Pathology, acknowledged that there were "just a few" cases who were "not sure how they acquired monkeypox." At least 75% of the individuals reported international travel, she said.

McQuiston added that cases have been from multiple states, and no area in the U.S. has been implicated in an urban outbreak of the virus, like Montreal. She said that community spread would be undetectable at this level, unless patients reported their symptoms to a healthcare provider.

As in prior briefings, McQuiston emphasized that recent cases of monkeypox have been reported without the preceding flu-like symptoms that were typical of "classic" monkeypox cases in Africa. Walensky said that some cases present with a rash around their genitals or anus prior to flu-like symptoms, whereas others never develop other symptoms.

"This has prompted concerns that monkeypox may go undiagnosed," she said.

Walensky urged clinicians to be suspicious of any "blister-like" rash, and cautioned not to rule out those with sexually transmitted infections, as there have been reports of monkeypox co-infections with syphilis, gonorrhea, chlamydia, and herpes.

McQuiston also said that CDC is working to expand upon the clinical symptoms of monkeypox to include some more unusual ones, such as proctitis, which is inflammation of the rectum, which can cause pain during defecation. She said the agency hopes to have additional information for clinicians next week.

For patients with monkeypox or close contacts at high-risk of contracting the virus, there are 72,000 doses of the Jynneos vaccine available in the strategic national stockpile, with 300,000 doses expected to be available over the course of several weeks, government officials said.

McQuiston stressed the importance of testing, adding that this will help to determine the extent of community spread if it happens, and Walensky agreed.

"We want to help everyone make an informed decision to protect their health and the health of their community," Walensky said.

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