Key ​​Me​ssages

• The California Department of Public Health has noticed recent increases in mpox cases and encourages providers to consider mpox in their differential diagnoses, test persons with suspected mpox, treat mpox, and offer vaccine to populations at increased risk to prevent severe mpox disease and reduce the number of new infections.  
• CDPH reminds health care providers how to recognize mpox, collect appropriate specimens, and provide treatment.  
• Providers are encouraged to consider mpox in the differential diagnosis of people with any diffuse or localized (e.g., genital) rash; along with syphilis, herpes, varicella, and molluscum contagiosum.   
• Since the beginning of September 2023, 44% of persons with mpox have reported having at least one dose of vaccine with 31% reporting having two doses.    
• While the mpox vaccine is effective at preventing illness and reducing disease severity, infections after vaccination are possible and testing is warranted among vaccinated persons who have compatible signs and symptoms. Vaccinated persons may have milder symptoms compared with unvaccinated persons, necessitating a low threshold for testing.  
• Because mpox continues to circulate in California, now is the time to promote vaccination in high-risk groups, however the vaccine is available to anyone who requests it.   
• People with HIV are at risk for severe manifestations of mpox, thus vaccination should be especially prioritized in people with HIV in these risk groups.  
• As mpox continues to circulate in California, vaccination of persons at risk continues to be important, especially with upcoming holiday gatherings.
• The risk of severe disease is greater in persons with HIV and less than 30% of people with HIV have received at least one dose of JYNNEOS in California.  Persons with HIV infection and risk factors for mpox exposure should be prioritized for education about mpox, vaccination, testing, and treatment.

Back​​ground

The California Department of Public Health (CDPH) would like to increase awareness of a recent increase in mpox cases in California and the nation. The number of California mpox cases has significantly increased from an average of approximately 1 to 7 cases per week from February to August 2023, up to approximately 17 cases per week in the most recent three-week period (September 20-October 10, 2023); 15 counties across California reported new cases in the most recent three-week period compared with 11 counties in the prior three weeks. In addition, the percent of positive mpox tests has increased from approximately 10% in July and August to 15-25% in September and early October. Case increases are also being seen in other parts of the country, including King County, Washington, North Carolina, and Hawaii. Importantly, most cases did not report travel or attending any specific event, suggesting ongoing transmission within sexual networks. Notably, since the beginning of September, over 40% of cases had at least one dose of vaccine and 31% had two doses, highlighting that while mpox vaccine is effective at reducing infections and disease severity, infections after vaccination are possible and testing is warranted among vaccinated persons.

Furthermore, wastewater surveillance data has detected mpox virus throughout the state for the past several months, indicating continued mpox circulation in California, including in areas without identified or reported infections.​ While the average number of weekly cases remains low compared with last year at this time, mpox continues to circulate in California, and recent data indicate that transmission levels are increasing.

Identifying Pa​tients with Mpox

1. It is important to remember that any person, regardless of gender identi​ty or sexual orientation, can become infected and transmit mpox if exposed.

• ​​Close, sustained skin-to-skin contact, including sexual contact, with a person with mpox appears to be the most significant risk factor associate​​d with mpox transmission. 
• In this outbreak, most of the reported infections have been in gay, bisexual, or other men who have sex with men (MSM).

2. ​K​eep mpox on the differential diagnosis for any diffuse or localized rash (including genital or perianal areas), particularly for those at high-risk for exposure. 

• Perform a complete physical exam (skin, oral mucosa, anal areas), as not all lesions are painful, and patients may be unaware of (or cannot see) lesions.
• Consider mpox in people who are already fully vaccinated or have been infected before, as mpox has occurred in people with prior infection or a partial or complete vaccination course.
• ​​Mpox may present with atypical, subtle, or mild symptoms and clinical presentation may depend on vaccination status or stage of lesion. 
• Evaluation for mpox in patients with rashes that may look like other common infections (e.g., syphilis, herpes, varicella, and molluscum contagiosum) should be considered.
• For more details on clinical presentations of mpox and mpox look-alikes, see CDC’s Mpox 101: What Clinicians Need to Know (PDF)​.
• Mpox infection may be concurrent with other STIs; thus, a diagnosis of another STI does not exclude mpox.

• ​Reported complications of mpox include severe pain, bacterial superinfection, severe pharyngeal swelling with concern for airway compromise, inability to eat/drink, and death.