Health officials in the US have confirmed 21 cases of monkeypox across 11 states amid a multinational outbreak that has grown to more than 800 cases in over two dozen countries.
In a press briefing Friday, the Centers for Disease Control and Prevention discussed details of the 17 US cases for which officials have clinical data. The officials noted that genetic sequencing from some of the cases revealed two distinct lineages of the monkeypox virus, which may indicate that monkeypox has been quietly spreading among humans for much longer than previously known. It also deepens concern over whether the current outbreak can be contained entirely.
Low risk overall
So far, there have been no deaths reported in the US or multinational outbreak. Among the 17 well-documented US cases, all patients are reported to be doing well and are isolating.
Though there have been two lineages identified in the outbreak, they fall into the clade of monkeypox virus dubbed the West African clade. This is the milder of two known monkeypox clades and has an estimated case fatality rate of 1 percent. The other clade is the Congo Basin clade, which has an estimated case fatality rate of up to 10 percent.
Monkeypox, which is endemic in animals in West and Central Africa, is not easily transmitted between humans. The large DNA virus spreads from human to human through close contact, including: direct, often sustained, skin-to-skin contact; direct contact with infected body fluids, particularly the fluids from skin lesions; direct contact with materials contaminated by bodily fluids or lesions, such as bed linens and clothing; and through respiratory droplets that typically require prolonged face-to-face interaction to transmit the virus.
Overall, with the relatively mild illnesses, no deaths, and poor transmission, public health officials, including those at the US CDC, continue to assess the risk to general public health as low.
"That being said, we don't want to minimize this condition," Jennifer McQuiston, deputy director of the CDC's Division of High Consequence Pathogens and Pathology, said in the press briefing Friday. "The rash caused by monkeypox virus can spread widely across the body or present in sensitive areas like the genitalia. It can be really painful, and some patients have reported needing prescription pain medicine to manage that pain. The sores can also cause long-term scarring on the skin."
Network spread
Most of the cases identified in the multinational outbreak continue to be in men who identify as gay or bisexual, or in men who have sex with men (MSM). Of the US cases discussed in the CDC briefing—which were published Friday in the CDC's Morbidity and Mortality Weekly Report—16 of the 17 cases were in MSM.
Although monkeypox is not considered a sexually-transmitted infection (STI), it can spread via close contact during sex. In the current outbreak, it appears the virus is spreading mainly through sexual networks. However, health officials continue to caution against spurring stigma. The large proportion of cases identified in MSM may partly reflect that many MSM have strong, established relationships with health care providers, particularly with sexual health services. Additionally, not all cases have been among MSM, and the virus will infect indiscriminately.
Clinical confusion
Typically in a monkeypox infection, infected people experience flu-like symptoms anywhere from four to 17 days after exposure, then one to four days later, a telltale rash develops. The deep-seated lesions start as flat and then fill with fluid before they eventually scab over. The lesions can spread all over but often concentrate on the face and extremities, particularly on the palms of hands and soles of feet.
But, in the current outbreak, some patients are presenting with atypical symptoms. Some see the rash before they have flu-like symptoms, and in many, the rash begins in the genital or perianal region before spreading. There are some reports that the rash is subtler than in classic monkeypox cases, which led some cases to be confused with STIs.
US detection
For instance, according to the MMWR report, the first US case identified in a Massachusetts man developed an anogenital rash on May 4, three days after returning from a trip to Canada. He subsequently went to outpatient health clinics on four occasions before being hospitalized on May 12 for the painful rash. It wasn't until hospital clinicians noted the reports of monkeypox cases in the United Kingdom that they suspected monkeypox. The patient tested positive for an Orthopoxvirus on May 17, which the CDC confirmed to be monkeypox on May 18.
Likewise, the second US case was in a man in New York City who developed oral and perianal lesions after travel and went to a health care provider on May 4. The man was presumed to have a common STI, was given treatment, then sent home. He was treated for a different STI when the rash progressed, though all STI tests were ultimately negative. Monkeypox was only suspected on May 19, after health officials reported the Massachusetts case.
Contact tracing
In all 17 well-documented US cases, the rashes began between May 1 and May 27. Authorities are still in the process of contact tracing all of those cases, but from 13 of the cases, authorities are monitoring more than 400 contacts so far. Of those, 56 are considered high-risk contacts, 117 are considered intermediate risk, and 235 have low or uncertain risk. Those at high risk are typically considered for post-exposure or prophylactic vaccination with one of two vaccines that can prevent monkeypox. There are also several treatment options available to those who do become infected, though none of the treatments is specific to monkeypox.
But authorities will have to do backward contact tracing to completely contain the outbreak in the US. Of the 17 cases, only 14 reported international travel in the three weeks before developing the rash. At least one case in an undisclosed state had no travel history and no clear contact with a known case—they do not know how they were exposed to the virus. This instance suggests that there is undetected community transmission underway in the US.
