Seasonal influenza activity in California is increasing with influenza A(H3N2) comprising the majority of currently circulating specimens. A newly emerged virus strain, H3N2 subclade K, is circulating globally and is now present in California. This strain is antigenically drifted from the H3N2 component of the 2025–26 seasonal influenza vaccine formulation and has been associated with earlier waves of influenza outbreaks in Canada, Japan, and the UK.
Key Messages
Influenza cases and hospital admissions are increasing in California. A newly emerged influenza A virus strain, H3N2 subclade K, is circulating globally, including in California. The majority of influenza A specimens subtyped in California are H3N2. Current influenza vaccines are still expected to offer protection against severe disease.
Administer 2025-26 influenza vaccine to anyone 6 months of age and older who has not yet received it.
Test symptomatic patients as quickly as possible. Use rapid molecular (nucleic acid amplification detection) tests for outpatients, and RT-PCR and other influenza molecular tests for hospitalized patients to confirm diagnosis and guide timely treatment. Influenza A positive hospitalized patients, especially those in the ICU, should have specimens sent for subtyping.
Initiate antiviral treatment without delay and ideally at point of care. Do not delay treatment while waiting for test results if influenza is suspected in high-risk patients. Treat immediately with oseltamivir or single-dose baloxavir based on recommendations for use. Treatment with influenza antivirals decreases the risk of serious illness and hospitalization in those at higher risk for severe disease.
CDPH is closely monitoring the increase in hospitalizations of Californians who have consumed foraged toxic mushrooms (death cap mushrooms, Amanita phalloides). Between mid-November and early December 2025, the California Poison Control System identified twenty-one cases of Amanita phalloides poisoning among persons who had consumed foraged wild mushrooms. As of December 5, 2025, twenty-one individuals who sought medical attention reported adverse effects, including acute liver injury and liver failure. Several patients have required admission to an intensive care unit, with one confirmed adult death to date. No cases been have identified in Orange County to date.
Health care providers should be aware of the potential for multiphase toxicity following wild mushroom ingestion. Gastrointestinal symptoms mimicking viral gastroenteritis can occur within 6 to 24 hours and typically resolve within 24 hours. This improvement can create a false impression of recovery as patients may still progress to potentially fatal hepatotoxicity within 48 to 96 hours after ingestion. Contact California Poison Control System at 1-800-222-1222 for guidance on diagnosing and treating patients with suspected mushroom poisoning.
Cases of Neisseria meningitidis have been reported among Orange County residents recently.
REMINDER: Due to the detection of ciprofloxacin-resistant strains of Neisseria meningitidis nationally, including in Southern California, public health and medical providers in California are recommended to discontinue the use of ciprofloxacin for invasive meningococcal disease (IMD) post-exposure prophylaxis (PEP).
Rifampin, ceftriaxone or azithromycin are recommended options for IMD PEP in California.
No changes to empiric treatment of IMD are recommended at this time.
As we head into the holidays, we wish you and yours a joyful and safe season.
Keep safety top of mind—on the road and in our communities. December marks National Impaired Driving Awareness Month, a reminder to make responsible choices and help protect one another.
Whether you're heading to a gathering or returning home to loved ones, please avoid driving under the influence of alcohol, cannabis, prescription medications, or other substances such as nitrous oxide. Impaired driving puts lives at risk and can have lasting consequences.
🎥 Click the image below to view a special holiday message from Dr. Jonathan Watson, Medical Director with Correctional Health Services reminding us all to celebrate safely and protect one another.
Stay safe, stay healthy, and enjoy a wonderful holiday season!
About Dr. Jonathan Watson
Dr. Jonathan Watson is dual Board-Certified in Family Medicine and Addiction Medicine and is the Medical Director of Orange County Correctional Health Services. He first discovered his passion for addiction care while working as a case manager in San Francisco’s Tenderloin neighborhood. He attended Harvard Medical School before pursuing his family medicine training at Harbor-UCLA Medical Center and then an addiction medicine Fellowship at UCLA. Dr. Watson’s love of teaching has pushed him to maintain volunteer clinical professor roles with UC Irvine’s Department of Family Medicine and Loma Linda University’s Department of Preventive Medicine. Dr. Watson has remained active with the California Society of Addiction Medicine.
Over the past month, influenza test positivity has steadily increased. Emergency department visits for influenza and RSV are also increasing. Although hospital admissions for these illnesses are increasing, overall hospitalization rates remain low. Notably, fewer influenza vaccines have been administered this year compared to the same period last year.
Currently, COVID-19 activity, as measured by percent positivity, remains low—lower than during the same period in each of the past five seasons.
Avian influenza A(H5N1) detections continue among wild birds and backyard poultry in the United States. Providers should evaluate patients with acute respiratory symptoms or conjunctivitis for avian influenza, especially if they have had recent exposure to animals or individuals suspected or confirmed to have the virus or have consumed raw dairy products. More info...
The Centers for Disease Control and Prevention (CDC) is issuing this Health Alert Network (HAN) Health Advisory to inform clinicians and health departments about a new outbreak of Marburg virus disease (MVD) in Ethiopia’s South Ethiopia and Sidama regions. MVD is a severe illness that can be fatal.
No suspected, probable, or confirmed cases of MVD related to this outbreak have been reported in the United States or other countries outside of Ethiopia as of December 3, 2025. The risk of spread to the United States is considered low at this time; however, clinicians should be aware of the potential for imported cases. As a precaution, this health advisory summarizes CDC’s recommendations about MVD case identification, testing, and biosafety considerations in clinical laboratories for U.S. health departments, clinical laboratories, and healthcare workers.
On November 17, 2025, CDC issued a Level 1 Travel Health Notice, advising people traveling to Ethiopia to practice usual precautions. The notice advises travelers to check their health for signs or symptoms of MVD while in the outbreak area and for 21 days after leaving and take appropriate actions (isolate, avoid travel, seek health care) if they become ill. Ethiopian national authorities are increasing response activities including screening, isolation of cases, contact tracing, airport exit screening, and public awareness campaigns to curb the spread of MVD. As of December 3, 2025, CDC is not recommending additional assessments or monitoring of travelers arriving from Ethiopia by the jurisdictional health departments.
World AIDS Day has been commemorated every December 1st since 1988. It is dedicated to spread awareness of the AIDS epidemic, to acknowledge all those living with HIV and to mourn all that have died of the disease.
World HIV/AIDS
Since 1988, 44 million people worldwide have died of AIDS and 40.8 million were living with HIV in 2024. There have been remarkable advances in HIV treatment, but HIV still claimed 630,000 lives in 2024. Despite advances in medications to prevent HIV infection, 1.3 million acquired HIV in 2024.
The theme of this year’s World AIDS Day is “Overcoming disruption, transforming the AIDS response.” This highlights the impact that funding cuts have had on the global HIV response. The cuts from international donors have threatened to undo decades of progress in HIV treatment and severely disrupt HIV prevention efforts.
The Joint United Nations Programme on HIV/AIDS (UNAIDS) calls for “sustained political leadership, international cooperation and human-rights-centered approaches to end AIDS by 2030.”
Orange County HIV
In Orange County, there were 6,955 persons living with HIV (PLWH) in 2024 that were aware of their status and an estimated additional 1,706 persons who are unaware they have HIV. The Centers for Disease Control and Prevention (CDC) estimates that 80.3% of PLWH know their status.
In 2024, 230 individuals in Orange County were newly diagnosed with HIV. This is a 14.8% decrease from 2020. Of these 230 people, 56 were diagnosed with AIDS at the time of their HIV diagnosis. This indicates they were likely infected for many years before getting tested.
Preventing HIV
Medications to prevent HIV are highly effective. These medications are called PrEP or pre-exposure prophylaxis. When the pills are taken on a regular basis, they are 99% effective to prevent getting infected. This year a new PrEP injection medication, Yeztugo (lenacapavir), was approved by the Food and Drug Administration. It is given as an injection under the skin but is only needed every 6 months. Those who are at risk of HIV infection need to know of the availability of PrEP no matter their insurance status.
Treating HIV
The advances in HIV treatment over the past two decades have changed the face of HIV care. It is now a very manageable, chronic disease. Most patients only have to take one pill, once-a-day and almost all patients can eliminate the virus completely from their blood. This is called being undetectable. When a person is undetectable, laboratory testing cannot detect any of the virus in the person’s blood. Without virus in the blood, the disease does not progress and the person remains healthy.
When a person is on medication and undetectable, they cannot pass the disease on to their sex partners. This concept is called U=U, undetectable mean untransmittable. You can learn more about U=U by clicking here.
Testing for HIV
A person can live a very long healthy life with HIV in 2025. It is a disease that is easily treated. But people need to know their HIV status so they can start treatment early, long before they might get sick. The CDC recommends everyone aged 13 to 64 get tested at least once as part of routine health care. Testing more frequently, every 3 to 6 months, is recommended for those at higher risk, especially gay or bisexual men, those with multiple sex partners and those who share needles during drug use.
On this 37th annual World AIDS Day, let’s reaffirm our collective commitment to ending the HIV epidemic:
It’s essential to ensure continued support and funding for HIV prevention and treatment programs.
Let’s talk openly about HIV, reduce stigma, and encourage testing for ourselves and our loved ones.
Help protect those at risk by increasing access to PrEP (pre-exposure prophylaxis).
And work to connect individuals living with HIV to life-saving treatment as early as possible.
Dr. Christopher Ried graduated from UC Berkeley and the UCLA School of Medicine. He did his residency at the UCLA/West LA Veterans Administration Medical Center and is Board Certified in Internal Medicine. He has been providing HIV care to the medically underserved for 34 years. For the past 25 years he has been the Medical Director of HIV/STD in the Public Health Services Division of the OC Health Care Agency.
