San Francisco has become the latest American city to confirm a case of the more dangerous Clade I strain of mpox, following a quiet yet concerning upward trend across the United States over the past two years. City health officials announced on Wednesday that the patient is an unvaccinated adult who was hospitalized but is now showing improvement. The individual had close contact with someone who traveled internationally, marking the first documented Clade I infection within San Francisco.
Not an Isolated Incident
This case is not an isolated event. Other jurisdictions in California, New York City, and various regions have now reported the Clade I strain, including several instances with no history of travel. This indicates the virus is no longer solely an imported problem and is establishing local transmission networks. Health officials note that mpox, formerly known as monkeypox, is primarily spreading locally among gay and bisexual men, without any known direct links to Africa where the strain is endemic.
Understanding Mpox and Its Severity
Mpox is a virus related to smallpox but generally milder. It typically causes symptoms including fever, swollen lymph nodes, significant body aches, and extreme fatigue. This is followed by the development of a painful rash, which can manifest as pimples or blisters on the face, hands, chest, genitals, or inside the mouth.
The rash progresses through distinct stages: beginning as flat spots, evolving into firm bumps, then transforming into pus-filled blisters, and finally forming scabs. The entire cycle can span several weeks, and individuals remain contagious from the onset of symptoms until every scab has fallen off and fresh skin has formed underneath.
The Heightened Concern with Clade I
The primary concern with the Clade I strain lies in its increased severity. During the 2022 outbreak, the United States predominantly experienced Clade II, which has a fatality rate of fewer than three percent among untreated patients. In contrast, Clade I has historically been associated with a mortality rate of up to ten percent of patients in African contexts, though medical experts suggest that advanced healthcare systems in the US would likely reduce this figure significantly.
Nevertheless, public health authorities are monitoring the spread with heightened vigilance. High-risk individuals are strongly encouraged to receive the two-dose JYNNEOS vaccine, which provides protection against both Clade I and Clade II strains.
Official Statements and Current Risk Assessment
'SFDPH is closely monitoring mpox,' stated Dr. Susan Philip, San Francisco's health officer. 'While Clade I mpox cases remain rare in the United States, clade II mpox cases continue to occur in San Francisco and throughout California.'
According to the Centers for Disease Control and Prevention (CDC), the risk posed by Clade I mpox to the general American population remains low. However, the agency considers the risk to men who have sex with men to be at a moderate level, warranting specific public health attention and preventive measures.
National Case Data and Transmission Patterns
The CDC reported that by March, the United States had recorded a total of 15 Clade I mpox cases, including four diagnoses within that month alone. All patients were reported to be in recovery. Each of these individuals had either traveled to Central or Eastern Africa, visited Western Europe where newer outbreaks are occurring, or had direct contact with someone who had undertaken such travel.
Federal health officials anticipate that additional cases will emerge in both Europe and the United States in the coming months. Clade I mpox spreads through the same mechanisms as Clade II, primarily via direct skin-to-skin contact. This includes sexual activity, but also extends to hugging, cuddling, kissing, and sharing items like bedding or towels.
While the virus can theoretically transmit from a pregnant person to a fetus, from animals to humans via bites or scratches, or through fluid contact, these routes are not currently driving the outbreak in the United States. A key unresolved question is whether mpox can spread through bodily fluids such as semen, vaginal fluid, urine, or stool.
Symptoms, Complications, and High-Risk Groups
Once the virus enters the body, it progresses slowly. Symptoms typically begin to appear one to three weeks after exposure. This prolonged incubation period means individuals can feel perfectly healthy, travel, and engage in intimate contact while unknowingly harboring and potentially spreading the virus.
The subsequent rash is often described by patients as causing 'agonizing' lesions, with pain so severe that basic activities like swallowing, walking, or sitting become unbearable. In severe instances, the sores can become infected with bacteria, potentially leading to sepsis. Some patients require hospitalization for advanced pain management, intravenous fluids, or antibiotic treatments.
Scarring represents one of the most debilitating long-term effects. Deep lesions can leave permanent pitted scars on sensitive areas such as the genitals, face, or even the corneas, with eye involvement posing a risk of vision loss. Unlike chickenpox, mpox lesions heal very slowly and can leave disfiguring marks for life.
Another hidden danger is posed to immunocompromised individuals, particularly those with untreated HIV, who face substantially higher risks of severe disease or death. In Africa, most fatal Clade I cases have occurred among people with underlying immune system deficiencies.
Vaccination Recommendations
Health authorities strongly advise that individuals who are male, transgender, nonbinary, queer, or gender non-conforming and have sex with men should consult their healthcare providers about vaccination. Furthermore, San Francisco health officials specifically recommend that anyone planning travel to a country where Clade I mpox is spreading—and who may have sex with a new partner while there, regardless of sexual orientation or gender identity—should also receive the JYNNEOS vaccine as a preventive measure.
